*snip*
Cassini launched on Oct. 15, 1997. It took a circuitous route, looping by Venus twice, then around Earth, and in 2000 it swung past Jupiter. With each planet flyby, the spacecraft robbed a little orbital energy from the respective planet to gain speed. The scheme saves fuel and makes the mission less expensive.
Cassini cameras have better detectors than the Voyager cameras did, Porco said, so when the spacecraft gets closer to its target it should produce clearer and sharper views than have ever been seen of Saturn.

"You can expect a real visual feast," Porco told SPACE.com. She said a regular flow of images should start in mid- to late-February.

"We will have very finely detailed images of atmospheric features like storms and waves, ring details that will exceed anything we've seen before by a factor of three to four, and resolution on some of the Saturn satellites fine enough to see features the size of an apartment building, if there are any!" she said. "We will know so much more than we do now."

Here's the one pic from Voyager giving us a glimpse of the mysterious moon "Mimas" dubbed "Death Star" by NASA scientists. Just one of many Saturn's moons.

More on Cassini Probe below....

The Huygens probe is attached to Cassini. It'll be a bonanza for planetary scientists.

"The Huygens Probe was named after Christiaan Huygens, a Dutch astronomer who in 1655 discovered Titan, Saturn's largest moon. The probe was designed by the European Space Agency (ESA), to perform an in-depth study of the clouds, atmosphere, and surface of Titan.

The Huygens probe will be plunging into a planetary atmosphere farther away from Earth than any other deep space probe has gone before.

Traveling onboard the Cassini orbiter throughout the seven-year journey to Saturn, the probe will undergo a series of in-flight tests and health checks to ensure that all of its instruments are working properly. This is essential, because the distance from Earth is too great to provide signals and commands. This means that the programming of the probe must be precise and work automatically so that valuable data can be communicated back to the orbiter and then back to Earth.

The 319-kilogram (703-pound) Huygens probe will separate from the Cassini orbiter in December of 2004, and will begin a 22-day coast phase toward Titan. Remaining on the Cassini orbiter will be the probe support equipment (PSE), which includes the electronics necessary to track the probe and to recover the data gathered during its descent. Then, in January of 2005, just 45 minutes before reaching the atmosphere of Titan, timers will wake up the Huygens probe.

As it finally enters Titan's atmosphere, three sets of parachutes will slow down the probe and provide a stable platform for scientific measurements. The fully instrumented robotic laboratory will reach the mysterious Titan's surface about two and half hours later."

Huygens is no small probe, just so one can picture it and envision that it's just an "attachment" to the much larger mother ship Cassini:

Cassini's relative size vs School Bus:

The Huygens probe is located on the rear left side (gold foiled disc)

A retrograde question.......Why is Titan more useful, easier, and/or more appealing to explore than Saturn itself? Is it because Titan is more exotic or hospitable?

Orangey Hazed Titan

By Robert Roy Britt
Senior Science Writer
posted: 06:00 am ET
16 October 2003

Plans have just been finalized for the Cassini spacecraft's exploration of Saturn's moon Titan, a giant world with a composition that resembles early Earth. Scientists expect the distant moon to help them understand the general nature of wind, oceans and how things might once have been on our home planet as well as Mars.

The investigation, which gets underway this summer, could also help theorists better model Earth's changing climate and the ultimate effects of global warming.

Titan is half the size of Earth and the only moon in the solar system with an atmosphere, which is loaded with methane and, like Earth's air, some nitrogen.

Ralph Lorenz, of the Lunar and Planetary Lab University of Arizona, presented the finished exploration plan over the weekend in Seattle at a meeting of the American Association for the Advancement of Science. It calls for 44 flybys of Titan over four years by Cassini after it arrives at Saturn this July. The craft will also deploy a probe to the surface of the moon next year.

Last week, Lorenz discussed with SPACE.com what he and colleagues hope to learn from Titan.

He explained that wind, waves and ocean currents are well understood only as they relate to current conditions on Earth. Scientists want to better grasp the underlying physics -- including what happens in wildly different conditions -- so they can predict how the natural world would react to change.

"We know that given the various factors that the result is X," Lorenz said. "We don't know for example, which of the factors is most important, or how the result will change if we change factor Y."

Earth's climate is heavily dependent on the transport of heat from equatorial regions to higher latitudes of the ocean and the atmosphere.

"Without, for example, the Gulf Stream, Northern Europe would be inhospitably cold, like much of Canada or Siberia at the same latitude," Lorenz said. "We don't know … whether global warming might cause that ocean circulation to shut down. The only tool we have for studying that sort of effect is computer modeling, and that has many uncertainties. Observing Titan's ocean circulation and climate will give us more data to refine these models."

Cassini launched in 1997 and studied Jupiter on its way toward Saturn. It has taken a long, looping path that included flybys of inner planets to get gravitational boosts that saved fuel and reduced mission costs.

Lorenz works on Cassini's radar mapping team and is a co-investigator of the Surface Science Package on the Huygens probe, which will sample the atmosphere before landing Titan or splashing into an ocean. Huygens' measurements will complement various observations made by Cassini during the flybys, from radar mapping to optical and near-infrared imaging and a probe of the moon's gravity field.

"It's an absolute bonanza of science in many different fields," Lorenz said.

If Titan has seas, their composition will be markedly different from those on our planet.

Last year, observations by the Arecibo radio telescope suggested Titan has oceans of methane and ethane -- what we call natural gas on Earth. Because Titan's surface is about -290 degrees Fahrenheit (-179 Celsius) both compounds would be liquid in the Titan seas.

How will waves and tides behave? How do these waves sculpt beaches? How deep are the seas and what is their relationship to the atmosphere?

Lorenz thinks answers to these and other questions could sharpen idea about early Mars, which is thought to have harbored oceans or lakes that might have been water-based.

"We don't know very well how to predict what the wind generation would be like with a different atmosphere and gravity," he said. "By seeing the process in action on Titan, we'll be able to make better predictions."

Titan also looks to scientists like a ripe, prebiotic world. It is perhaps similar to Earth in its early era, before life developed. Theorists will try to use Titan's chemistry, once explored, to figure out how our own planet made the leap from lifeless to life bearing.

"Titan is the largest single unexplored piece of real estate in the solar system," Lorenz said, "and with an atmosphere and probably a hydrological cycle as well, it's likely to be the most interesting."

Ocean Studies May Be Heading to Space
By PAUL RECER, AP
SEATTLE (Feb. 14) - The skills and technology used to explore the extreme depths of the Earth's oceans will soon find work in outer space. Scientists are making plans to probe the icy seas of Jupiter's moons and drop a lander to the bizarre gasoline-like lakes of Titan, a moon of Saturn.

"The possibilities of studying the extraterrestrial oceans in the solar system is now real," said Torrence Johnson, a scientist at the Jet Propulsion Laboratory.

Johnson, speaking Saturday at the national meeting of the American Association for the Advancement of Science, said researchers are drawing up plans to send orbiters to Ganymede and Europa. The two Jupiter moons may be covered with oceans under miles-thick layers of ice.

Oceanography, said Johnson, is no longer just an Earth science.

"The universe is awash with water," he said. "Europa probably contains twice as much water as all of the oceans of Earth."

Early plans call for orbiting the Jovian moons with craft that can measure tides and penetrate ice with special radar. These are techniques that oceanographers have used to probe the Earth's waters.

Later plans would mean landing packages on the icy surfaces and perhaps drilling down, searching for liquid water, the most likely domain of life, Johnson said.

Some researchers believe radioactive and tidal heating may form deep reservoirs of liquid water beneath the ice and that life forms may exist there, enduring the extreme pressures and darkness. Oceanographers have found some bacteria living in such conditions in the Earth's black depths.

Johnson said planetary scientists are leaning on long-tested techniques that oceanographers have used.

"We are turning to our oceanographic colleagues who make things work at the unbelievable pressures," said Johnson.

Studies for the exploration of the oceans of Jupiter's moons will be completed next year. Johnson said the National Aeronautics and Space Administration will draw up plan for the projects.

Exploration of the surface of Titan, a moon of Saturn, will start even sooner. The Cassini spacecraft, launched seven years ago, will reach Saturn in July and drop a probe to the moon's surface in January.

Titan, a frigid world about half the Earth's size, is the only moon in the solar system with a thick atmosphere. Smog generated by a thick nitrogen atmosphere four times denser than the Earth's obscures Titan's surface.

"Titan is the largest piece of unexplored real estate in the solar system, said Ralph Lorenz, a University of Arizona planetary scientist and a leader of the Cassini project.

Radar images from Earth telescopes and infrared photos from the Hubble Space Telescope have penetrated Titan's smog and detected bright and dark regions.

An analysis of the infrared data suggests the dark regions are seas of methane and ethane, hydrocarbons that could form compounds similar to gasoline.

"The simplest explanation may be that these smooth areas are lakes or seas," Lorenz said.

Deep below the surface of Titan, through miles of ice, scientists believe there may be oceans of liquid water, perhaps saturated with organic compounds that could support life.

"If you introduce microbes into that then they may survive," Lorenz said.

He said if internal heat from Titan caused water to geyser up into the atmosphere, the resulting chemistry would produce many organic molecules, perhaps forming amino acids necessary for life.

"It will be interesting to explore how far Titan has gone toward organizing life," he said, But, he added, "I don't expect to find any living Titans."

02/14/04 14:59 EST

Copyright 2004 The Associated Press

Donald Savage
Headquarters, Washington February 27, 2004

Carolina Martinez
Jet Propulsion Laboratory, Pasadena, Calif.

Heidi Finn
Space Science Institute, Boulder, Colo.
(Phone: 720/974-5859)

RELEASE: 04-073

CASSINI CAPTURES STUNNING VIEW OF SATURN

Four months before its scheduled arrival at Saturn, the
Cassini-Huygens spacecraft sent its best color postcard back to
Earth of the ringed world. The spacecraft is expected to send
weekly postcards, as it gets closer to the ringed giant.

The view from Cassini shows Saturn growing larger and more
defined as the spacecraft nears a July 1, 2004, arrival date.
On February 9, Cassini's narrow angle camera, one of two
cameras onboard the spacecraft, took a series of exposures
through different filters, which were combined to form the
color image released today.

"We very much want everyone to enjoy Cassini's tour of this
magnificent planetary system," said Dr. Carolyn Porco, leader
of the Cassini imaging science team at the Space Science
Institute in Boulder, Colo. "And I can say right now the views
out the window will be stunning," Porco said.

Cassini was 69.4 million kilometers (43.2 million miles) from
Saturn when the images were taken. The smallest features
visible in the image are approximately 540 kilometers (336
miles) across. Finer details in the rings and atmosphere than
previously seen are beginning to emerge and will grow in
sharpness and clarity over the coming months. The thickness of
the middle B ring of Saturn, and the comparative translucence
of the outer A ring, when seen against the planet, as well as
subtle color differences in the finely banded Saturn
atmosphere, are more apparent.

"I feel like a kid on a road trip at the beginning of our
tour," said Dr. Dennis Matson, project scientist for the
Cassini-Huygens mission to Saturn and its largest moon Titan.
"We've been driving this car for nearly 3.5 billion kilometers
(2.2 billion miles) and it's time to get off and explore this
ringed world and its many moons. I can hardly wait, but in the
meantime, these weekly color images offer a glimpse of our
final destination," Matson said.

In the coming months, imaging highlights will include near
daily, multi-wavelength imaging of Saturn and its rings;
imaging of Titan beginning in April; Titan movie sequences
starting in late May, when the resolution exceeds that
obtainable from Earth; and a flyby of Saturn's distant moon,
Phoebe, in June, at a spacecraft altitude of 2,000 kilometers
(1,243 miles).

Through Cassini, about 260 scientists from 17 countries hope to
gain a better understanding of Saturn, its famous rings, its
magnetosphere, Titan, and its other icy moons. "Cassini is
probably the most ambitious exploration mission ever launched
and is the fruit of an active international collaboration,"
said Dr. Andre Brahic, imaging team member and professor at
Universite Paris 7-Denis Diderot, France. "It should be the
prelude of our future, the exploration of our surroundings by
humanity," Brahic said.

Cassini will begin a four-year prime mission in orbit around
Saturn when it arrives July 1. It will release its piggybacked
Huygens probe about six months later for descent through
Titan's thick atmosphere. The probe could impact in what may be
a liquid methane ocean.

JPL, a division of the California Institute of Technology in
Pasadena, manages the mission for NASA's Office of Space
Science, Washington. The Space Science Institute is a non- profit organization of scientists and educators engaged in
research in astrophysics, planetary science, Earth sciences,
and in integrating research with education and public outreach.
Cassini-Huygens is a cooperative mission of NASA, the European
Space Agency and the Italian Space Agency

For the first image and other weekly images on the Internet
each Friday, visit:

http://www.nasa.gov

http://ciclops.org

For information about Cassini-Huygens on the Internet, visit,

http://saturn.jpl.nasa.gov

-end-

* * *

March 12

Cassini Views Clumps in Saturn Ring

Clumps seemingly embedded within Saturn's narrow, outermost F ring can be seen in these two Cassini narrow angle camera images taken on Feb. 23, 2004 from a distance of 39 million miles (62.9 million kilometers)

The Cassini images were taken nearly two hours apart using a filter in an onboard camera.

The core of the F ring is about 31 miles (50 kilometers) wide, and from Cassini's current distance, is not fully resolvable. Contrast has been greatly enhanced, and the images have been magnified, to aid visibility of the F Ring and the clump features. Like all particles in Saturn's ring system, these features orbit the planet in the same direction in which the planet rotates.
It is not certain what causes these features, though several theories have been proposed, including meteoroid bombardment and inter-particle collisions in the F ring. Scientists have only a rough idea of the lifetime of clumps in Saturn's rings - a mystery that Cassini may help to answer.

The small dot at center right in the second image is one of Saturn's small moons, Janus 112 miles (181 kilometers) across.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The imaging team is based at the Space Science Institute, Boulder, Colorado.

By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
31 March 2004

Saturn's moon Titan might be one of the most out-of-this world places to hang ten, according to new computer modeling that suggests a given wind could generate waves there that are seven times taller than on Earth.

Scientists aren't sure if Titan has seas, but they suspect it does based on hard-to-interpret telescopic observations. The oceans would be made mostly of ethane and methane, studies show.
Because Titan's gravity is about one-seventh that of Earth, any wind-driven waves would behave differently than they do here.

"Big-wave riding could take on a whole new meaning on Titan," says Nadeem Ghafoor of Surrey Satellite Technology in the UK.

Ghafoor and colleagues considered several factors -- Titan's gravity, the likely composition and density of the atmosphere and any possible seas, and probable wind speeds -- to generate wave scenarios using modified version of terrestrial ocean computer models.

The development of waves depends on wind speed and how long and over what distance it blows in one direction, called the "fetch."

The Titan model incorporates wind speeds up to a modest 12.5 mph (5 meters per second). "We do not know much about the surface winds on Titan, although early models suggest the sustained wind speed at the surface is likely to be low," Ghafoor explained. The model includes fetches up to 620 miles (1,000 kilometers). "Much of the Titan wave growth happens before 100 kilometers [62 miles] is reached, however," Ghafoor said.

"Waves grow to be up to seven times higher and longer than those on Earth," Ghafoor told SPACE.com. "However because of the lower gravity on Titan, waves on Titan will generally appear to move in slow motion."

Ghafoor is slated to present the results today at a meeting of the Royal Astronomical Society. He said the computer model is sound, but he allows that the make-up of Titan's surface -- liquid or solid -- involves speculation at this point.

"Something weird is happening down there, however, and it seems that we may only truly know when Cassini-Huygens arrives in January 2005," Ghafoor said, referring to the Cassini mission to Saturn. The craft carries the Huygens probe, which will plunge through the atmosphere and land on Titan's surface -- whatever it's made of -- early next year. If Huygens lands in a sea, it could float and transmit data for up to two hours.

The probe has instruments that could measure the height and frequency of any waves and the liquid's composition. With sonar, it could measure the sea's depth. Its camera might even return the first pictures of an extraterrestrial sea.

"What would we see?" wonders Open University professor John Zarnecki, a participant in the new study and leader of Huygens' Surface Science Package experiment.

"Well, the waves would be more widely dispersed than on Earth but they will be very much higher," Zarnecki said. "So the surface around us would probably appear flat and deceptively calm, but in the distance we might see a rather tall, slow-moving wave advancing towards us -- a wave that could overwhelm or sink us."

Weird Object Beyond Pluto Gets Stranger
By Robert Roy Britt
Senior Science Writer
posted: 02:07 pm ET
14 April 2004

Update: First posted at 1 p.m. ET

When astronomers announced the discovery last month of Sedna, the most distant known object in the solar system, they were nearly certain it had an unseen satellite. New observations by the Hubble Space Telescope find no moon, however, deepening the mystery surrounding this already strange object.
Images

Hubble made 35 images of Sedna on March 16, 2004. Sedna moves with respect to a much more distant background star. The movement is due not to Sedna's plodding orbital pace, but to Earth's quicker motion around the Sun. Astronomers use the resulting "parallax" to determine Sedna's distance. No moon appears in the images.

Sedna is about three-fourths the size of Pluto. It is so far away that it takes 10,000 years to orbit the Sun. Its discovery has astronomers arguing over whether to call it a planet or a planetoid, and whether to count it as one of many objects in the Kuiper Belt, where Pluto roams, or the first known example of an expected halo of more distant objects called the Oort Cloud.

Caltech astronomer Mike Brown, who led the discovery, said Sedna's slow rotation rate had him convinced there was an unseen satellite exerting a gravitational tug.

Here's why: Most objects in the solar system that don't have companions complete a rotation, or day, in a matter of hours. There are many examples of fast-spinning asteroids and similarly whirling large, round Kuiper Belt objects. Pluto, on the other hand, has had its rotational period slowed to six Earth-days by its companion, Charon.

Sedna spins on its axis once every 20 Earth-days, or perhaps even more slowly, making the presence of a moon practically inevitable, Brown had thought. So shortly after the discovery, Hubble was pointed at Sedna.

"Much to our surprise, there's no satellite," he told reporters today.

'Completely baffled'

"I'm completely baffled at the absence of a moon," Brown said. "This is outside the realm of expectation and makes Sedna even more interesting. But I simply don't know what it means."

The rotation of Sedna, officially named 2003 VB12, was determined by noting changes in brightness from its surface during repeated ground-based observations over about 3 months. Brown and his colleagues assumed differences in surface composition accounted for the changes. At first they determined the rotation period was 40 days. They later refined that to learn that it's at least 20 days, and possibly still as much as 40.

After the Hubble observations, the researchers considered that maybe they had not properly analyzed the data. But a "careful reanalysis" leaves them convinced they've determined the possible range of the rotation period accurately.

"I'm completely lost for an explanation as to why the object rotates so slowly," Brown said.

There remain some possibilities for a rational explanation.

There's a small chance that during the Hubble observations, the suspected satellite of Sedna was hidden, lurking either directly behind or directly in front of Sedna. Or a satellite might have throttled Sedna's rotation long ago, then been destroyed in a collision or lost in a gravitational interaction with a planet.

Or, Sedna might rotate every 25 hours instead of 24 days, a setup that could fool astronomers into drawing their present conclusion. This latter possibility can be confirmed or ruled out with more observations.

All these scenarios are seen as unlikely. More likely, Brown figures, is that the satellite is darker than expected and simply didn't show up.

"Even though it's quite large, it could be quite dark," he said. "We still very strongly believe there is or was a satellite."

Brown said the moon would be about 400 miles wide, or 2.5 times smaller than Sedna and six times fainter. Further attempts to locate the satellite might be made with other telescopes, with fresh expectations for how to look.

Brown's colleague, Yale University researcher David Rabinowitz, has a slightly different opinion of the results.

The Hubble observations "rule out a large moon," Rabinowitz said. If there is something there, he said, it is 10 times smaller than Sedna and it's not clear it could have slowed Sedna's rotation rate.

Refining the diameter

Brown said the observations of Sedna are equal to spotting a soccer ball at 900 miles away. Hubble was unable to resolve Sedna as a disk, so an exact size can't be determined. But that shortcoming sets an upper limit of about 1,000 miles on its diameter, based on assumptions of how much light it reflects. If Sedna has a brighter surface than assumed, it could be smaller.

Pluto is 1,413 miles (2,274 kilometers) wide.

Given Hubble's unsurpassed ability, Brown does not know how Sedna's diameter will be firmly determined until a new generation of telescopes come online in the next decade.

Meanwhile, astronomers still are not sure where or how Sedna formed or how it came to travel on such a long, looping orbit. While Pluto's orbit is, on average, 39 times the Earth-Sun distance, Sedna roams from 76 to 1,000 times the Earth-Sun distance.

Answering questions about the strange object's origins, orbit and rotation -- along with similar discoveries of other distant objects -- will help researchers clarify the now-fuzzy picture of the outer solar system.

-end-

Strange Shadows: Saturn's Two-Faced Moon
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
26 April 2004

Clear as black and white, Saturn's moon Iapetus is two-faced. One half is dark as coal and the other is as bright as fresh linens. Astronomers have puzzled over the stark difference since late in the 17th Century.

New radar observations hint at what's going on, but the mystery is far from solved.

Saturn's outermost large moon, Iapetus, has a bright, heavily cratered icy terrain and a dark terrain, as shown in this Voyager 2 image taken on August 22, 1981. The dark material covers precisely the side of Iapetus that leads in the direction of orbital motion around Saturn (except for the poles), whereas the bright material occurs on the trailing hemisphere and at the poles.

Iapetus is 907 miles (1,460 kilometers) wide and circles Saturn at a distance of about 2.2 million miles (3.6 million kilometers). Like Earth's Moon, Iapetus' rotation and orbit are in lockstep, both taking 79 Earth-days, so that it always shows the same face to Saturn. That's not the strange part.

Oddly, the side of Iapetus that always faces forward as it moves along its orbital path -- think of the front of a race car on a circular track -- reflects just 5 percent of the sunlight that hits it. The trailing hemisphere is much brighter, reflecting 50 percent of sunlight.

Possible causes

In the early 1980s, Voyager 2 photographed the remarkable dichotomy but did not explain it.

Astronomers have theorized that perhaps the front face is dark because it picks up debris, just as the front bumper of the race car is peppered with tire rubber, grease and whatever else the other cars cast off. With Iapetus, the debris might be bits of another moon, Phoebe, whose whole surface is relatively dark. The material might be kicked up from Phoebe by small meteor impacts, the thinking goes.

But dark Phoebe, which orbits backward and is probably a captured asteroid, is not precisely the same color as the dark face of icy Iapetus.

And there's another puzzling fact: The dark material on Iapetus seems also to be concentrated in the bottoms of some craters. That led to speculation long ago that the chemical or mineral or whatever it is perhaps oozes from within.

The state of confusion is based on visible evidence. Now scientists have scanned the moon with radar, using the Arecibo Observatory in Puerto Rico.

The picture is not a whole lot clearer, but some interesting twists emerge.

First, the bright news

"It is known that the bright side is mostly water ice, but we find it does not reflect the radar like other icy satellites that we've studied with the radar before," says study leader Gregory Black of the University of Virginia. "The ice on Iapetus appears much less reflective."

Clean water ice should be radar-bright, so the ice on the front hemisphere of Iapetus must contain some radar-darkening material.

"We think that most likely this is a bit of ammonia ice mixed in with the water ice," Black told SPACE.com. The frozen concoction would not reflect radar waves as well as clean water ice, he explained, and yet it could still look like clean ice in optical observations.

The light and dark sides of Iapetus, in a rendering based on Voyager data.
IMAGE © SCIENCE
The results were reported last week in the journal Science.

Astronomers had suspected ammonia might be present in the moons of Saturn, but it has never been directly detected. The radar observations seem to offer the strongest evidence yet for its existence. Curiosities continue, however.

Now, the dark news

"Another surprise is that the radar system sees Iapetus as a uniform object, meaning no difference between the light and dark sides," Black said.

That could mean that on the dark side there is merely a thin coat of some darkening material over the ammonia-laden water ice, like an inch of dirt atop clean snow, Black said.

"A thin coating would not have much effect on the radar reflection, which sees the underlying ice, and therefore both sides would look the same in radar but differently optically," he said. "This interpretation depends somewhat on what the dark material is made of, but we are not able to answer that question."

A better picture could emerge when the Cassini spacecraft conducts a thorough examination of the Saturnian system beginning this summer. It is expected to make fresh observations of Iapetus in perhaps one or more close flybys.

Cassini will improve on the Voyager observations, providing visible and infrared views "that will be better able to determine compositions, in particular that of the dark material, or directly detect ammonia," Black said. The space probe will also focus on the sharp boundary between the light and dark hemispheres, and that could help explain whether the stuff wells up from within or bombards Iapetus from the outside.

"Cassini will certainly help enormously," Black said, "although I'm not sure I can say if it will solve these issues completely."

If Cassini does unlock the secrets of the mysterious moon, it will complete a centuries-long circle of investigation.

The spacecraft is named for Italian astronomer Giovanni Domenico Cassini, who discovered Iapetus in 1671. Cassini later saw that while the moon was visible on one side of Saturn, it disappeared when its orbit took it around to the other side. He correctly deduced that Iapetus kept one face toward Saturn and that it had a split compositional personality.

...it won't be long now....

Cassini in Saturn's Clutches

On May 18, the Cassini spacecraft entered the Saturn planetary system, where the gravitational pull of Saturn overtook the influence of the Sun and we crossed the outer limits of the most distant group of the planet's moons.

In this new image, the craft captured three moons. Prometheus (102 kilometers, or 63 miles across) and Pandora (84 kilometers, or 52 miles across), shepherd the planet's narrow F-ring. Prometheus overtakes Pandora in orbit around Saturn about every 25 days.

The F-ring is a narrow, ribbon-like structure, with a width seen in this geometry equivalent to a few kilometers. The two small, irregularly shaped moons exert a gravitational influence on particles that make up the F ring, confining it and possibly leading to the formation of clumps, strands and other structures observed there.

Slightly above the pair and to the right is another moon, Epimetheus (116 kilometers, or 72 miles across). The image was taken on May 1, 2004, at a distance of 31.4 million kilometers (19.5 million miles) from Saturn. The image has been magnified and greatly contrast-enhanced to aid visibility. It was released yesterday.

Early next month, the spaceship will make its closest approach to Phoebe, the largest member of the outer moon population and perhaps a captured asteroid. The probe will explore Saturn and its moons, including deploying its piggybacked Huygens probe, which will descend through the smog of the largest moon, Titan.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The imaging team is based at the Space Science Institute, Boulder, Colo.

Cassini revolved Prometheus and Pandora in an earlier image, too.

-- SPACE.com Staff

Credit: NASA/JPL/Space Science Institute

Carolina Martinez
(Phone: 818/354-9382)
Jet Propulsion Laboratory, Pasadena, Calif.

RELEASE: 04-186

CASSINI SPACECRAFT NEAR FIRST STOP IN HISTORIC SATURN TOUR

The most complex interplanetary mission ever launched
is about to meet one of the solar system's enigmatic moons.
Cassini will fly by Phoebe, Saturn's largest outer moon, on
Friday. The closest approach is at approximately 4:56 p.m.
EDT.

A final trajectory correction maneuver is scheduled for
June 16. On arrival date, June 30, Cassini will become
the first spacecraft to orbit Saturn. Once in orbit it
will conduct an extensive, four-year tour of the Saturn
system, including its majestic rings and many known
moons.

"The arrival date and trajectory to Saturn were specifically
selected to accommodate this flyby, which will be the only
opportunity during the mission to study Phoebe at close
range," said Dave Seal, mission planner for the Cassini- Huygens mission at NASA's Jet Propulsion Laboratory (JPL),
Pasadena, Calif. "Phoebe's orbit is simply too far from
Saturn, at almost 13 million kilometers (about 8 million
miles), nearly four times as far as the next closest major
satellite, Iapetus. A later encounter is not feasible."
"The last time we had observations of Phoebe was by Voyager
in 1981," said Dr. Torrence Johnson, former Voyager imaging
team member, Galileo project scientist and Cassini imaging
team member. "This time around, the pictures of the
mysterious moon will 1,000 times better, as Cassini will be
closer," he said. Voyager 2 captured images of Phoebe from
about 2.2 million kilometers (about 1.4 million miles) away.
Cassini will obtain images from a mere 2,000 kilometers
(about 1,240 miles) above the moon's surface.
Cassini will also collect spectroscopic and radar data that
could decipher the composition and origin of this distant
moon. Cassini's Phoebe images, already twice as good as
returned by Voyager 2, show large craters and variations in
surface brightness.
te Phoebe will be heavily cratered in the higher resolution
images we expect to see in the next few days," said Dr.
Peter Thomas, a member of the imaging team and a senior
research associate at Cornell University, Ithaca, N.Y., who
specializes in studies of small satellites. "The hints of
different brightness also suggest the highest resolution
images, several hundred times better, will show a variety of
materials," he said.
Discovered in 1898 by American astronomer William Henry
Pickering, Phoebe is of great interest to scientists. "With
the instruments Cassini carries, we might learn more about
Phoebe's internal structure and composition. What we have
are many unanswered questions: Did it ever melt? Does it
have evidence of past interior melting? Was it ever an icy
body? Why is Phoebe in such an odd orbit?" said Dr. Dennis
Matson, project scientist for the Cassini-Huygens mission at
JPL.
Phoebe has a diameter of 220 kilometers (about 136.7 miles),
which is equal to about one-fifteenth of the diameter of
Earth's moon. Phoebe rotates on its axis every nine hours
and 16 minutes, and it completes a full orbit around Saturn
in about 18 months. Its elliptical orbit is inclined
approximately 30 degrees to Saturn's equator. Phoebe's
retrograde orbit means it goes around Saturn in the opposite
direction of the larger interior Saturnian moons. Previous
ground-based observations have shown water ice present on
its surface.
Phoebe is also unusual as it is very dark. It reflects only
six percent of the sunlight it receives. Phoebe's darkness
and retrograde orbit suggest it is most likely a captured
object. A captured object is a celestial body caught by the
gravitational pull of a much bigger body, generally a
planet. Some scientists believe Phoebe might even be an
object from the outer solar system, similar to the objects
found in the Kuiper Belt. The Belt is a collection of small
icy bodies beyond Pluto that were never drawn together by
gravity to form a planet.
"The dark and odd-shaped Phoebe may be a piece of the
building blocks from which some of the planets formed," said
Dr. Bonnie Buratti, scientist on the Cassini-Huygens mission
at JPL. "It might hold clues about the early formation of
our solar system."

Cassini's first pics of Phoebe, gets a lot better very soon...

The Cassini-Huygens mission is a cooperative project of
NASA, the European Space Agency and the Italian Space
Agency. JPL, a division of the California Institute of
Technology, Pasadena, manages the Cassini-Huygens mission
for NASA's Office of Space Science, Washington. JPL
designed, developed and assembled the Cassini orbiter. For
the latest images and information about the Cassini-Huygens
mission on the Internet, visit:
http://www.nasa.gov/cassini
For information about NASA and agency programs on the
Internet, visit:
http://www.nasa.gov

-end-

* * *

Saturn's Moon Phoebe: Old, Beaten and Still Mysterious

By Robert Roy Britt
Senior Science Writer
posted: 06:30 am ET
15 June 2004

You have to appreciate Phoebe's rugged mug, a face weathered by time, with deep and shadowed sockets complemented by sharp ridges, a brooding darkness accented by highlights visible upon close inspection. It is a look of survival etched over 4.5 billion years.

And if preliminary analyses of new images are correct, this tiny moon of Saturn is quite the wanderer, a vagabond of the frigid fringes of the solar system that's been lured inward, grabbed by Saturn's mighty gravity, and turned into an awkward satellite.

Phoebe was visited Friday by the Cassini spacecraft. The successful flyby exposed the small world in unprecedented detail and portends a rich survey of the Saturnian system, a mission that will include 52 flybys of seven moons.

Way back

Phoebe looks a lot like an asteroid. It's just 137 miles (220 kilometers) wide and riddled with craters. It is roughly spherical but by no means perfect.

Scientists have long suspected Phoebe is instead an object captured from the Kuiper Belt, a more distant region of icy bodies beyond Neptune. There were already clues: Phoebe is oddly dark for a moon and it orbits backward compared to the rotation of Saturn and the paths of the planet's larger moons.

If Phoebe is from the Kuiper Belt, it could be a very useful, unsullied specimen of the early solar system, an object that gathered itself together before the planets had finished forming and which has changed little since.

While most asteroids are chips of larger objects, Kupier Belt Objects probably collided less often -- Phoebe may never have been any bigger than it is now. That's important, because it would mean Phoebe is probably too small to have ever had a melted core, so its contents could be pristine, a window to the chemicals and minerals of the solar system at birth.

The new pictures hint at Phoebe's primordial nature.

Mostly ice

Surface features and the way in which light reflects are "subtly different" from asteroids, said Peter Thomas, a senior research associate at Cornell University and a specialist in the study of small satellites. "I can't quantify it yet," Thomas told SPACE.com yesterday. "It's just sort of an impression."

Some of the bright areas on the small moon may be material from below -- possibly water ice -- that's been exposed by impacts. Thomas said it's too early to know for sure. But if a full analysis shows Phoebe to be composed largely of ice, that would almost guarantee it came from beyond. Asteroids contain little ice and are made mostly of rock and metals.

"If it turns out there's a lot of ice in this thing, then it's safe to say its not asteroidal," Thomas said. He points out, though, that nobody really knows what a Kuiper Belt Object should look like.

Carolyn Porco, Cassini Imaging Team leader at the Space Science Institute in Boulder, Colorado, also sees hints of a lot of ice beneath the surface of Phoebe in layers evident along the crater walls.

"The dark stuff we're seeing is just a coating on the surface," Porco said in a telephone interview. "We think the body is probably ice-rich."

Firm answers await a full analysis of the many tests run on Phoebe during the flyby.

Working 'like a charm'

Meanwhile, as one of the most complex, multifaceted space probes ever built, the $3.3-billion Cassini mission has shown it can deliver on one of its main tasks. The size of a small school bus, it flew within 1,285 miles (2,068 kilometers) of Phoebe at a relative speed of 13,000 mph (20,900 kilometers per hour) while 11 separate instruments gathered data.

An onboard autonomous target tracker "seemed to work like a charm," Porco said.

Radar probed the surface down to nearly 8 inches (20 centimeters). Cassini also recorded ultraviolet and infrared light. Phoebe's gravitational effect on the spacecraft was noted. From all this and more, astronomers expect to determine the moon's exact mass and density, create a detailed global surface map, and figure out a lot about what it's made of.

"The best thing is the spacecraft actually did this complicated encounter," said Thomas, the Cornell researcher. "We're hoping to do this off-and-on for four years. It's very reassuring to know we can."

Cassini's next major milestone will come at the end of this month, when the plutonium-powered probe settles into its first of 76 planned orbits around Saturn. Early next year it will release the Huygens probe, which will land on the surface of Titan, Saturn's largest Moon.

The Cassini-Huygens mission is a project of NASA, the European Space Agency and the Italian Space Agency.

Closing in on Titan

The Cassini spacecraft beamed back this new, more detailed image of smog-enshrouded Titan on June 14.

This view represents an improvement in resolution of nearly a factor of three over the previous Cassini image release about Titan. The observed brightness variations are real on scales of a hundred kilometers or less.

The image was obtained in the near-infrared through a polarizing filter. The combination was designed to reduce the obscuration by atmospheric haze. The superimposed coordinate system grid in the accompanying image at right illustrates the geographical regions of the moon that are illuminated and visible, as well as the orientation of Titan -- north is up and rotated 25 degrees to the left. The yellow curve marks the position of the boundary between day and night on Titan.

This image shows about one quarter of Titan's surface, from 0 to 70 degrees West longitude, and just barely overlaps part of the surface shown in the previous Titan image release. Most of the visible surface in this image has not yet been shown in any Cassini image release.

The image was obtained with the narrow angle camera at a phase, or Sun-Titan-spacecraft, angle of 61 degrees and at a distance of 6.5 million miles (10.4 million kilometers) from Titan. The image scale is 39 miles (62 kilometers) per pixel. The image was magnified by a factor of two using a linear interpolation scheme. No further processing to remove the effects of the overlying atmosphere has been performed.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

Image Credit: NASA/JPL/Space Science Institute

ARRIVAL! Cassini Enters Orbit Around Saturn
By Leonard David
Senior Space Writer
posted: 01:20 am ET
01 July 2004

BOULDER, COLORADO -- The Cassini tour bus to Saturn has arrived. After a nearly seven year journey, the spacecraft swung into an orbit around the giant gas globe tonight, ready to spend the next four years performing scientific investigations of the Saturnian system.

Beginning Wednesday evening, an engine on the nearly six-ton spacecraft throttled up and fired for more than 90 minutes, slowing Cassini down and placing it into an initial orbit around Saturn. That maneuver is called the Saturn Orbit Insertion, or SOI.

The SOI burn was critical to the success of the mission at Saturn. Cassini approached Saturn from below the planet’s ring plane, crossing through the large gap between the F Ring and G Ring.

Saturn's ring system is divided up into 7 major divisions, with the innermost ring to the outermost ring designated as D, C, B, A, F, G and E Ring. Each major ring division is further subdivided into thousands of individual "ringlets". These are made of ice particles and rocky material.

The spacecraft’s main engine was turned to face the direction of travel, and the resulting thrust from the engine acted as a braking device, slowing down the spacecraft as it entered Saturn's orbit.

Price tagged at over $3 billion, the mission is the most ambitious planetary mission ever conducted.

More moons?

Cassini’s engine burn lasted 96 minutes, placing the spacecraft into a highly elliptical orbit around Saturn.

The spacecraft’s closest approach to Saturn during its basic four-year tour occurred during the engine firing. The spacecraft's distance from Saturn was about 11,184 miles (18,000 kilometers), or less than a sixth of Saturn's diameter.

Cassini is now continuing to coast above the rings for approximately one hour and 44 minutes before its descent back through the ring plane.

As Cassini begins surveying the Saturnian system, ahead for the spacecraft is at least 76 orbits around the ringed planet, including 52 close encounters with seven of Saturn's 31 known moons. Scientists speculate that more moons orbiting the planet may still await discovery.

Extended mission

Program managers and scientists have already begun to discuss an extended Cassini mission, beyond the four-year primary mission. That extended mission might last 4 to 6 years, perhaps as much as 8 years if onboard fuel holds out.

Along with an array of science instruments, Cassini is toting the European Space Agency’s Huygens probe. The probe’s task is to parachute into the thick atmosphere of Titan -- Saturn's largest moon -- in mid-January of next year.

The Cassini-Huygens mission is an international undertaking led by three space agencies: NASA, the European Space Agency and the Italian space agency, Agenzia Spaziale Italiana (ASI). Seventeen nations contributed to building the spacecraft. The project is managed by the Jet Propulsion Laboratory (JPL) in Pasadena, California.

Anxious scientists

Numbers of anxious space scientists have gathered here tonight at the Colorado University’s Laboratory for Atmospheric and Space Physics (LASP). And for good reason.

Onboard Cassini is a $12 million CU-Boulder instrument -- LASP's Ultraviolet Imaging Spectrograph, or UVIS. It is one of the 12 scientific instruments that the craft has hauled to Saturn.

The UVIS instrument package has a set of telescopes to measure UV light reflected by or emitted from Saturn's atmosphere, its rings and its moon atmospheres and surfaces. The data collected can determine their compositions, distribution, aerosol content and temperatures.

Name plate

Kip Denhalter, an electronics engineer at LASP helped build the UVIS instrument.

"There’s a sense of accomplishment. In the case of UVIS, an added feature on our flight instrument is that there’s a plate on the back to cover all the cables. All the people that worked on it, our names are nicely engraved on that plate. So we’ve got our names in orbit around Saturn, Denhalter said. "It’s kind of neat to point to Saturn and say I’ve got something I worked on out there," he told SPACE.com.

Alain Jouchoux, operations team leader for the UVIS, said he expects the device to keep working for many, many years – far beyond Cassini’s initial exploration goal of four years. "It can work forever," he confidently added.

Best photos in our lifetime

"Officially, we’re in orbit," said Jim Crocker, Vice President, Civil Space for Lockheed Martin Space Systems in neighboring Denver, Colorado. "We really needed to nail it and it looks like we did. This will give us a lot of science," he told SPACE.com in a phone interview.

Lockheed Martin built the spacecraft’s propulsion system, 16 thrusters, the nuclear power generators, and assembled a camera that is onboard the Huygens probe.

Crocker said imagery from Cassini is forthcoming. "These will be the best images of the rings that we’ll see in our lifetime," he added. "We’re very happy. Of course this is only the beginning. We’ve got four years to go and we’ll be firing up the engine a number of times."

*snip*
Ringscapes

Dominating today’s JPL press briefing were first close-up pictures of "ringscapes" , along with small sheparding moons that tend Saturn’s rings.

In one striking blowup, Porco pointed out what almost looks like straw, clumps of material within Saturn’s A Ring. "I don’t know what this is…I literally don’t have a clue."

"The beauty and clarity of these images…they are shocking to me," Porco said. "We are seeing structure, literally, that we’ve never imaged before."

Porco said that pictures to be taken by Cassini during the next four years will be roughly 300,000 in number, equaling about 100 a day, sometimes more, sometimes less....

Ken - Have you read an explanation for the perturbations in the rings here? Sampleing or conversion error? Actual oscillation in the rings?

PASADENA, Calif. (AP) -- Scientists on Saturday released what they called the best pictures yet of the frozen surface of Saturn's enormous moon Titan but said they were puzzled that the Cassini spacecraft hadn't glimpsed any evidence of liquids.

The latest images of Titan revealed a single set of clouds about the size of Arizona and dark and light shapes across the moon that the imaging team continued to analyze.

The shots of the moon's surface features were taken during Cassini's first pass Friday at a distance of about 200,000 miles.

"It's different from anything we've ever seen before," imaging scientist Elizabeth Turtle said. "We're still trying to understand the surface of Titan."

One indistinct circular shape could be a huge crater, and a linear shape could be a hydrocarbon river or a fault line, scientists said.

Scientists believe the moon could have chemical compounds much like those that existed on Earth billions of years ago before life appeared.

Big enough to be a planet in its own right, Titan has an atmosphere 1 1/2 times as dense as Earth's, containing organic -- meaning carbon-based -- compounds. Scientists believe there could be hydrocarbon seas or lakes.

Turtle said initial data analysis suggested the moon is the site of some type of geologic activity that could include wind and erosion and development of the lakes or rivers.

Kevin Baines, a member of the visual and infrared spectrometer team, said scientists were disappointed that they hadn't seen evidence of liquids through reflections of sunlight on smooth surfaces of the moon.

We thought we'd see some flashes, and we haven't seen any. So we're a little perplexed,'' he said after a news conference at NASA's Jet Propulsion Laboratory in Pasadena.

Among the new pictures released were four images of a cluster of clouds near Titan's south pole that are believed to be composed of methane. They were the only brightly distinct spots on otherwise fuzzy images of Titan.

"Someone likened it to a melting ice cream sundae," Turtle said.

Near-infrared images of Titan prompted scientists to question previous theories about the moon's surface. They had thought brighter areas of the moon were thick layers of ice and darker areas were a mixture of substances including hydrocarbons, but they said it appears the opposite is true.

There will be many more chances to uncover the face of Titan during Cassini's planned four-year tour. The spacecraft will make 45 more flybys of the moon -- coming with 600 miles of Titan at times -- and then send a probe into its atmosphere in January.

The probe, named Huygens, will send pictures back to Cassini as it makes a 2 1/2-hour descent by parachute through the atmosphere.

Titan was Cassini's first encounter since the spacecraft began orbiting Saturn earlier this week.

The $3.3 billion mission, funded by NASA, the European Space Agency and the Italian Space Agency, was launched in 1997. The spacecraft flew 2.2 billion miles on a roundabout route to Saturn.

The Cassini spacecraft is putting together an impressive if preliminary image scrapbook of Saturn's moons, including this new view of Mimas.

Mimas (pronounced MY-mass) is small, just 247 miles (398 kilometers) wide. It sports a crater, named Herschel, that at 80 miles (130 kilometers) wide and 6 miles (10 kilometers) deep is remarkably large in comparison to the moon.

The photo, released this week, was taken July 3 just after Cassini entered orbit around Saturn. The craft was about a million miles (1.7 million kilometers) from Mimas. Cassini will get closer photos of Mimas later in the 4-year mission, and it will conduct close flybys of several other Saturnian satellites, too.

Mimas is one of the innermost of Saturn's 31 known moons. It's made largely of ice, astronomers think.

A Different Crescent Moon

The Cassini spacecraft is collecting early images of Saturn's moon in what will be a four-year survey of the whole system. This new view of Rhea, the second largest satellite of Saturn, is one sign of things to come.

With a diameter of 1,528 kilometers (950 miles) across, Rhea is Saturn's second largest moon. It has one hemisphere covered bright streaks that might be water frost, scientists learned long ago from they Voyager spacecraft.

Like Earth's Moon, Rhea is heavily crated, the result of ancient impacts by other space rocks. And seen from the right angle, as here, Rhea can show off a crescent phase, just as Earth's Moon does.

Cassini is slated to fly by Rhea at a distance of only 311 miles (500 kilometers) on Nov. 26, 2005. This view was taken from about 615,000 miles (990,000 kilometers) away.

Saturn's Two-Faced Moon

The Cassini spacecraft has returned its first clear picture of Iapetus, the two-faced moon of Saturn. There are better images to come.

Iapetus (pronounced eye-APP-eh-tuss) is one of Saturn's 31 known moons. One hemisphere is very dark, and the other is very light, owing to different surface compositions (what you see in this picture is not a shadow!). Scientists don't know what's going on. But Cassini aims to find out.

The strange moon has a leading hemisphere that appears to be coated with some sort of dark material, and a more reflective trailing hemisphere. The differences are revealed by reflected sunlight -- the same thing that makes all planets and moons visible.

Iapetus is about 892 miles (1,436 kilometers) wide, or about one-third the diameter of Earth's moon.

This image was taken in visible light from about 1.8 million miles (3 million kilometers miles) away. During Cassini's four-year tour of the Saturn system, the spacecraft will conduct two close encounters of Iapetus, including one at just 622 miles (1,000 kilometers) from the moon's surface.

Spectacular Detail

Saturn's rings have been seen in many colors. Attempts to highlight the contrast resulted in a garish image from the Voyager mission. Infrared or ultraviolet imagery is colorized so otherwise invisible radiation reflected by the ring particles are pleasing to our eyes.

This new view from the Cassini spacecraft captures the true colors of the rings, according to astronomers at the Space Science Institute, which manages the probe's camera.

Cassini was beneath the rings on June 21, about 4 million miles (6.4 million kilometers) from Saturn when it took this picture. It was released yesterday.

Saturn has several rings separated by distinct gaps. The ring system begins from the inside out in this order: D, C, B, A, F, G, E.

The brightest part of the rings in this image, curving from the upper right to the lower left, is the B ring. Many bands throughout the B ring have a pronounced sandy color. Cassini's images show that color variations in the rings are more pronounced in this viewing geometry than they are when seen from Earth.

The rings are made primarily of water ice with, as Cassini showed recently, rock or mud sprinkled in. Since pure water ice is white, it is believed that different colors in the rings reflect different amounts of contamination by other materials such as rock or carbon compounds.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.

Carolina Martinez
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-9382)

RELEASE: 04-259

SATURN'S SHADOW AND TITAN'S GLOW SHED LIGHT ON A COMPLEX SYSTEM

The Cassini spacecraft, which began its tour of the Saturn
system just over a month ago, has detected lightning and a new
radiation belt at Saturn, and a glow around the planet's
largest moon, Titan.

The spacecraft's radio and plasma wave science instrument
detected radio waves generated by lightning. "We are detecting
the same crackle and pop one hears when listening to an AM
radio broadcast during a thunderstorm," said Dr. Bill Kurth,
deputy principal investigator on the radio and plasma wave
instrument, University of Iowa, Iowa City. "These storms are
dramatically different than those observed 20 years ago."

Cassini finds radio bursts from this lightning are highly
episodic. There are large variations in the occurrence of
lightning from day to day, sometimes with little or no
lightning, suggesting a number of different, possibly short- lived storms, at mid- to high latitudes. Voyager observed
lightning from an extended storm system at low latitudes, which
lasted for months and appeared highly regular from one day to
the next.

The difference in storm characteristics may be related to very
different shadowing conditions in the 1980s than they are now.
During the Voyager time period when lightning was first
observed, the rings cast a very deep shadow near Saturn's
equator. As a result, the atmosphere in a narrow band was
permanently in shadow -- making it cold -- and located right
next to the hottest in Saturn's atmosphere. Turbulence between
the hot and cold regions could have led to long-lived storms.
However, during Cassini's approach and entry into Saturn's
orbit, it is summer in the southern hemisphere and the ring
shadow is distributed widely over a large portion of the
northern hemisphere. This causes the hottest and coldest
regions to be far apart.

A major finding of the magnetospheric imaging instrument is the
discovery of a new radiation belt just above Saturn's cloud
tops, up to the inner edge of the D-ring. This is the first
time that a new Saturnian radiation belt has been discovered
with remote sensing.

This new radiation belt extends around the planet. It was
detected by the emission of fast neutral atoms created as its
magnetically trapped ions interact with gas clouds located
planetward of the D-ring. With this discovery, the radiation
belts are shown to extend far closer to the planet than
previously known.

"This new radiation belt had eluded detection by any of the
spacecraft that previously visited Saturn. With its discovery
we have seen something that we did not expect, that radiation
belt particles can 'hop' over obstructions like Saturn's rings,
without being absorbed by the rings in the process," said Dr.
Donald G. Mitchell, instrument scientist for the magnetospheric
imaging instrument at the Johns Hopkins University Applied
Physics Laboratory, Laurel, Md.

Saturn's largest moon, Titan, is also shining for attention.
Cassini's visual and infrared mapping spectrometer captured
Titan glowing both day and night, powered by emissions from
methane and carbon monoxide gases in the moon's extensive,
thick atmosphere.

"Not only is Titan putting on a great light show but it is also
teaching us more about its dense atmosphere," said Dr. Kevin
Baines, science team member for the visual and infrared mapping
spectrometer at Jet Propulsion Laboratory, Pasadena, Calif.
"What is amazing is that the size of this glow or emission of
gases is a sixth the diameter of the planet," he added.

The Sun-illuminated fluorescent glow of methane throughout
Titan's upper atmosphere -- revealing the atmosphere's immense
thickness and extending more than 700 kilometers (435 miles)
above the surface, was expected. However, the nighttime glow,
persistently shining over the night side of Titan, initially
surprised scientists.

"These images are as if you were seeing Titan through alien
eyes. Titan glows throughout the near-infrared spectrum. If you
were an alien it would be hard to get a good night's sleep on
Titan because the light would always be on," Baines said.

The Cassini-Huygens mission is a cooperative project of NASA,
the European Space Agency and the Italian Space Agency. JPL
manages the Cassini-Huygens mission for NASA's Science Mission
Directorate, Washington.
For the latest images and more information about the Cassini- Huygens mission, visit
http://saturn.jpl.nasa.gov
http://www.nasa.gov/cassini
-end-

* * *

Colorized Titan

This new image from the Cassini spacecraft shows Saturn's moon Titan in ultraviolet and infrared wavelengths. It was taken Oct. 26 during a close flyby and released yesterday.

The image is constructed from four observations acquired through different color filters. Red and green colors represent infrared wavelengths and show areas where atmospheric methane absorbs light. These colors reveal a brighter (redder) northern hemisphere. Blue represents ultraviolet wavelengths and shows the high atmosphere and detached hazes.

Titan has a gigantic atmosphere, extending hundreds of miles above the surface. The sharp variations in brightness on Titan's surface (and clouds near the south pole) are apparent at infrared wavelengths.

Scientists are still analyzing images and data from the flyby in an effort to better plan the descent of Cassini's Huygens probe to the surface of Titan later this year.

The unexplained bright cloud formation is about 20 degrees off the southern axis. The inset shows the Huygens probe landing site. Credit: JPL/Space Science Institute

New Images of Titan Baffle Astronomers
By Henry Bortman
Astrobiology Magazine
posted: 28 October 2004
12:17 pm ET

Instruments aboard the Cassini spacecraft have sent back the most detailed images ever captured of the surface of Saturn's giant moon, Titan. They've also presented scientists with a major mystery.

There's a huge cloud formation over the moon's south pole, spanning 620 miles (1,000 kilometers) at its widest. That's no surprise; scientists expected it to be there. But they also expected it to be made of methane. And it isn't.

There's lots of methane in Titan's atmosphere. It was detected many years ago by spacecraft that flew past the ringed planet. So when recent images from the Keck Observatory in Hawaii showed clouds at Titan's south pole, scientists assumed they were methane clouds. According to their model, Titan is so cold that methane can form liquid pools on its surface.

When this liquid is heated by the sun, it evaporates, forming methane clouds.

Water clouds on Earth work the same way. The sun heats the ocean, water evaporates and clouds form in the atmosphere. Because Titan's south pole is currently pointed toward the sun, it is receiving the greatest amount of heat right now. So a massive cloud form over the south pole fits the model perfectly - if the cloud is made of methane.

The problem

But, according to data gathered by Cassini, the particles that make up the cloud are too big to be methane.

"I don't believe it," says Chris McKay, a planetary scientist with the NASA Ames Research Center in Moffett Field, California. "What else can they be? It would be like flying over Earth and saying the clouds are not water. If those clouds are really not methane, then a lot of the things we think about Titan are wrong. A lot of things we think about those clouds are wrong - the whole explanation of why they're there."

The Cassini science team has not yet had time to fully analyze the data sent back by the spacecraft, so they don't yet know what the clouds are made of.

One possibility, McKay speculates, is ethane. But ethane, he says, is a photochemical product that is produced in the upper atmosphere and rains downward. So it wouldn't make sense that a massive ethane cloud would appear at the south pole.

Organic goo?

Another possibility, he says, is that "it's some sort of organic goo. It could be some sort of organic polymer, essentially plastic particles. Maybe little polystyrene foam balls. Who knows?" But, as with ethane, these would form from above. There's no known reason why a massive cloud of them should form at Titan's south pole.

And so, McKay concludes, freely admitting that his off-the-cuff theory is "based on no data," that the clouds "are formed of methane, and that there's some process which is hiding the spectral signatures of the methane."

One plausible scenario is that the cloud particles could start out as methane, produced as expected on the ground and carried aloft. Once airborne, however, they become coated with some other substance, perhaps ethane. Further study of the spectral data collected by Cassini, together with lab-based experiments should enable scientists to unravel the mystery, but it will take some time for them to do so.

Meanwhile, down on Titan's surface, another mystery is unfolding. Recent images have revealed stunning surface detail, never before seen. But, according to Caroline Porco, team leader for the imaging science subsystem, "we don't know exactly what we're looking at." The "don't know" part applies both to the moon's surface composition and to its topography.

Figuring out what the moon is made of should be relatively easy, using data from Cassini's VIMS (Visual and Infrared Mapping Spectrometer) instrument. Different materials reflect light at different frequencies. Each pixel captured by VIMS records the strength of the light reflected at each of 352 distinct frequencies. Some of these frequencies are visible to human eyes, others are in the infrared.

By analyzing this spectral data, scientists should be able to figure out Titan's surface composition. The analysis requires intensive computation, matching the observed spectra to standards stored in spectral libraries here on Earth. Early results should be available within a few days.

Surface mysteries

Titan's topography will be a tougher nut to crack.

Because of the global haze layer, Porco says, "we do not see shadows on the surface of Titan. And because we don't see shadow, we can't look at an image and immediately deduce what's up and what's down." There could be massive mountains and deep valleys there, or the surface could be completely flat. At this point, there's no way to tell.

Titan is unlike Mars and the icy moons of Jupiter, which have little or no atmosphere. So the "techniques that we've used for interpreting airless bodies, all those methods of examining solid surfaces from planetary spacecraft that we have learned over the last half century," don't apply, says Porco. "We can't use that on Titan, because it's a very different environment."

What scientists can use is a combination of data from several different Casssini instruments, collected over a long period of time. During its 4-year mission, Cassini will make many more close passes by Titan, 45 in all.

During these future flybys, Cassini will collect both radar data - the first such data was captured during Tuesday's flyby - and stereo images. By integrating these two types of data, the Cassini science team will be able slowly to build up a picture of Titan's topography. That process, however, will take months - or even years.

Splash, Thud, or Whimper? Cassini's Huygens Probe Rendezvous with Titan

By Cynthia Phillips
SETI Institute
posted: 23 December 2004
06:34 am ET

On December 24th, 2004, at 7:08 PM Pacific Standard Time, the Cassini spacecraft will release a probe that has hitched a ride all the way from Earth out to Saturn. The Huygens Probe, named after the Dutch scientist Christiaan Huygens, who discovered Titan and Saturn’s rings in the 17th century and built by the European Space Agency, will spend 22 days traveling to its rendezvous with Saturn’s mysterious moon Titan on January 14th. Titan is one of the remaining puzzles of the solar system – while Cassini’s imaging cameras and radar instrument have begun to reveal the details of its surface, the Huygens probe will be the first spacecraft to venture beneath Titan’s thick clouds

Since the Huygens probe doesn’t have its own means of propulsion, its release point will be carefully timed so that its trajectory will take it right to Titan. The Cassini spacecraft will change course slightly so that it flies past Titan, but doesn’t impact it. Once Huygens is released, it will be in a coasting configuration, with its scientific instruments turned off except for a timer that will wake up the spacecraft just before it reaches Titan.

Huygens’ first encounter with Titan will be when it reaches the top of Titan’s atmosphere. Due to Titan’s low gravity, its atmosphere is ten times deeper than Earth’s – the outer limits are at 600 km above Titan’s surface! The probe will wake up when it first detects the outer fringes of atmosphere. As Huygens descends on its parachutes through Titan’s thick atmosphere, it will use a group of six instruments to study the mysterious moon. Huygens has enough battery power to survive for between 2.5 and three hours, which includes a descent time to the surface between 2 and 2.5 hours, plus at least a few minutes (and up to half an hour) of operating time on the surface, assuming it survives the landing.

The descent through Titan’s atmosphere is carefully choreographed, with a series of parachutes deploying at certain intervals to slow the probe’s downward trajectory. Once the velocity is slow enough and temperatures are safe, the heat shield at the bottom of the spacecraft will be jettisoned and the scientific instruments it was protecting can begin to take data. These instruments include the Gas Chromatograph Mass Spectrometer (GCMS) and the Aerosol Collector and Pyrolyser (ACP), both of which will measure the composition of Titan’s atmosphere.

The Huygens Atmospheric Structure Instrument (HASI) will deploy on a boom to measure the structure of Titan’s atmosphere, including its density, pressure, and temperature at various altitudes, and the Descent Imager / Spectral Radiometer (DISR) camera will begin taking panoramic images as the spacecraft spins on its parachute. DISR is planned to take more than 1100 images during the descent. Shortly before landing, DISR will switch on a special lamp to measure the reflection spectrum of Titan’s surface, to help determine its chemical composition. Also during Huygens’ descent, the Doppler Wind Experiment (DWE) will use the shifts in the radio signals sent from Huygens back to Cassini to determine the wind direction and magnitude at various points in Titan’s atmosphere.

Once Huygens reaches Titan’s surface, the Surface Science Package (SSP) will make surface measurements with nine different sensors. Since we do not even know if Huygens will land on a solid or liquid surface, the sensors are designed to take measurements of a wide variety of materials, including both solid and fluid properties. These measurements include such basic physical properties as conductivity, thermal properties, acoustic properties, fluid permittivity, fluid density, and refractive index.

The Cassini spacecraft has a three-hour window to listen to the signals transmitted from Huygens; after that time has elapsed, Cassini’s trajectory will have carried it out of sight of the probe (and the probe’s battery will be used up soon after). Cassini will then turn its antenna toward Earth and start transmitting what it has received from Huygens. Stay tuned on January 14th and beyond for some amazing discoveries!

Liquid methane sea/shoreline perhaps?

This composite was produced from images returned yesterday, January 14, 2005, by the European Space Agency's Huygens probe during its successful descent to land on Titan. It shows the boundary between the lighter-colored uplifted terrain, marked with what appear to be drainage channels, and darker lower areas.

Upcoming Cassini
2005 Moon Encounters
Enceladus: Mar. 9
Titan: Mar. 31
Titan: Apr. 16
Enceladus: July 14
Titan: Aug. 22
Titan: Sept. 7
Hyperion: Sept. 26
Dione: Oct. 11
Titan: Oct. 28
Rhea: Nov. 26
Titan: Dec. 26

More pics & data at site below:

By Cynthia Phillips, Ph.D.
SETI Institute
posted: 20 January 2005
06:46 am ET

With the successful landing of the European Space Agency’s Huygens probe on Saturn’s moon Titan, we can now bring the number of bodies in the solar system that have been landed on by a spacecraft up to four (or five, if you count the soft-crash-landing of the NEAR spacecraft on the asteroid Eros). The Moon has been the most visited, with robotic landers from the former Soviet Union and from NASA, as well as six successful landings with astronauts in the late 1960’s and 1970’s. The planet Venus was visited by four successful unmanned landers from the former Soviet Union in the 1970’s, and the planet Mars has been visited successfully by a variety of NASA robotic landers starting in the 1970’s with the two Viking landers, 1997’s Mars Pathfinder, and 2004’s Spirit and Opportunity rovers.

So what have we learned from this planetary exploration? While orbiting spacecraft can map the surfaces of planets, and provide big-picture geological context, there’s no substitute for actually landing on the surface of another world to get an idea of what it’s really like there. Especially for us humans, it’s much easier to picture ourselves on the ground of an alien world with pictures taken from the surface than with pictures taken from orbit. You can imagine that you’re really there, and sometimes there’s just no substitute, scientifically, for a little pretended sightseeing.

The accompanying image contains landscapes from spacecraft that have landed on three worlds with atmospheres – Venus, Mars, and now Titan. Airless bodies like the Moon have a very different surface environment, which is mainly shaped by eons of impact cratering. On airless worlds, this cratering results in a thick, broken-up surface layer called a regolith that appears as a softened, dusty layer a few meters thick or more.

Planets or satellites with atmospheres, on the other hand, have a whole range of available geological processes that can shape their surfaces. While the surface of the Earth is primarily shaped by liquid water, even in the most arid regions, as well as by the presence of life, drier worlds like Venus and Mars have different landscapes. Even a cold, dry place like Mars, however, shows signs of geological activity produced by liquid water in many places – water is such an effective agent of geological change that even relatively ancient, or rare, occurrences may be preserved and appear dominant. The other major geological factor is wind – even on Mars, with its relatively thin atmosphere, wind has sculpted the surface, smoothing rocks and distributing dust on a global scale.

The surface of Mars is, of course, heterogeneous – different regions of the surface vary distinctly in appearance and predominant geological activity. Think of the views from the recent Spirit and Opportunity landers, for instance. Still, some regions of Mars look strikingly similar, as in the Spirit and Viking 2 lander images shown here. The surface is strewn with rocks, some of which have been smoothed by the action of water or wind over geological time. The rocks are interspersed with patches of smoother sandy soil.

Worlds like Venus are much harder to understand. Venus is a planet predominantly shaped by volcanic activity. While we have only a few views of the surface of Venus under its thick clouds (a similar situation to Titan), the view from Venera 9 is strikingly similar to the views of Mars. Rocks are seen, although they are more angular and less weathered than the rocks visible on Mars, perhaps due to the dense atmosphere which limits surface wind speeds on Venus to a few km/hour. Acid rain may also produce some chemical and mechanical weathering of rocks at the surface. Other regions of the surface of Venus have a smoother, more plate-like appearance, perhaps due to a different sort of volcanic activity.

Perhaps most surprising in our views of worlds with atmospheres is the new view of Titan’s surface. Titan, with its thick atmosphere, extremely cold surface temperature, and suspected surface composition of various exotic hydrocarbons, would seem worlds away from the comparatively more Earth-like inner solar system. Yet the surface image from Titan, shown here, reveals a surprisingly familiar-looking surface – blocks of material, thought to be water and/or hydrocarbon ice, are interspersed with regions of darker, smoother-looking material that appears similar to the dust or soil seen between rocks on Mars or Venus. The ice blocks of Titan even appear to have some erosion at their bases that could be due to fluvial processes.

It seems unlikely that three worlds that are so different – hot, volcanic Venus, with a surface temperature of over 700 K; cold, dry Mars with a surface temperature of about 200K; and even colder, exotic Titan with a surface temperature of about 94K – could have surfaces that appear so similar. Yet the similarities are striking – the view of Titan’s surface could easily be mistaken for the more familiar Mars, or even for Venus! In fact, some dry, arid regions of the Earth itself have a similar appearance.

While our new view of Titan’s surface might seem almost disappointingly familiar for such an exotic place, it is perhaps an indication of the commonality of geological processes everywhere in the solar system. This fact should be reassuring – the action of wind and fluids produces similar results whether the temperature is near the melting point of rock or cold enough to freeze most volatile materials. Material is emplaced onto the surface, whether molten rock or molten ice, and then acted upon by liquids and gases over millions of years, causing it to slowly degrade. Apparently, these processes result in a similar appearance, independent of surface temperature or atmospheric thickness.

The analysis of the Huygens results is just beginning, and doubtless we will find many ways in which Titan is completely unlike anywhere else in the solar system. Perhaps it is reassuring, then, that we at least think we understand some of the fundamentals, even if the details are completely unknown and probably exotic. The solar system is a pretty amazing place!

Titan: A World of Its Own

By Seth Shostak
SETI Institute
posted: 03 February 2005
06:24 am ET

OK, everyone anticipated that Titan was going to be interesting, but few expected it to be weirder than Michael Jackson (sigh, this clown can't even escape science newz).

Two weeks ago, as the Huygens probe parachuted through this distant moon’s oily, pumpkin skies, a less-than-consumer-grade 0.04 megapixel camera was trained on the landscape ten miles below. It saw a hostile shoreline, riven with tributaries, and what appears to be a (possibly dry) lake.

Imagine the luck: a shoreline and a lake. Try dropping a penny on a big map of your home state, and see how often it lands on a bit of shoreline topography. Not often, unless you live in Minnesota. The implication is that Titan is pockmarked with ponds; it’s Minnesota trapped in the mother of all winters. Daytime temperatures are an unpleasant -180 C (-290 F).

But the cold hasn’t immobilized this moon. Titan’s crater-free surface, the tributaries, the broken topography… indeed the whole scene tells you that something is going on here, despite the big chill. There’s geology on the move. This is not Europa’s frozen rictus, or even Mars’ gelid, dust-blown desert.

"This is a place with a combination of stability and dynamic flow," says David Grinspoon, of the Southwest Research Institute. "It’s the kind of location where we might find life."

Life? Now there’s a thought. For years, textbooks and talking heads have explained why a mission to Titan was worth the euros because it might reveal something about the start of life on our planet. The claim was that Titan’s atmosphere is rather similar to Earth’s early air. So maybe this hydrocarbon-coated moon could help us unravel the genesis of terrestrial biology, at least if atmospheric chemistry was an important factor.

Well, you can forget that, says Bruce Jakosky, of the University of Colorado. "The reasons we originally looked to Titan are long gone. The putative reducing atmosphere of the early Earth -- one that was oxygen poor and hydrogen rich -- is no longer in fashion." Titan is its own world, and not a time capsule of our own.

That’s one reason why the existence of life on Titan would be big news. It would be life-as-we-don’t-know-it.

A Tough Environment

Fair enough. But is it there? Is there really any chance that microbial Titans are tucked away in this moon’s sticky, cruddy landscape? Most pundits are doubtful. They wave their arms at two major difficulties:

To begin with, there’s no liquid water on the surface. It’s frozen harder than a graduate math exam. That seems to be a real problem for biologists. Rocco Mancinelli, of the SETI Institute, notes that "the solvent system for earthly life is water. Sure, there might be lakes of liquid ethane and methane on Titan, but the biological compounds we know about just don’t dissolve in those."

The other problem is the temperature, lower than a lounge lizard’s moral character. This is not a matter of comfort, but of chemistry. If you recall what was taught you in high school, you’ll know that chemical reaction rates slow down as the thermometer drops. A quick calculation using the Arrhenius equation suggests that, at –180 C, chemistry is 16 orders of magnitude more sluggish than at room temperature. In other words, even if life cooked up on Earth in five minutes, it will still be another 100 billion years before it might do so on Titan. (Mind you, this calculation is included here merely to draw the ire of chemists, who will undoubtedly e-mail me with a come-uppance. But there’s no doubt that cold will be a hindrance to metabolism.)

Of course, you might solve both problems by going underground. There’s a decent chance that ammonia-water aquifers lurk under Titan’s surface, and that could be good news for life. "An ammonia-water mixture is, to me, just as exciting as liquid water reservoirs," says Grinspoon. But Jakosky points out that any sudsy, subterranean retreats would be far from the surface, where the food supply might be.

Food and Warmth

Which raises the point: what could tiny Titans possibly eat? The surface is choked with hydrocarbon compounds, and while you might prefer to use them for heating your house or fueling buses, they could presumably be food for the right kind of microbes. Grinspoon notes that ultraviolet light from the sun will convert some of Titan’s methane and ethane-rich upper atmosphere into acetylene. "These energy-rich, big acetylene molecules would fall to the surface and accumulate," he suggests.

It would be kind of like having wheat fields in the sky. Acetylene manna from heaven. "And if microscopic Titans feed on this stuff, maybe they’d give off some body heat, making their own little liquid water holes."

That’s not something you see every day: acetylene-powered life, staving off the cold with its own body heat. But if metabolism doesn’t provide enough warmth, Jakosky offers some other ideas for beating the sub-zero conditions of the surface. "After all, you have impacts from incoming space rocks that careen into Titan. The impacts will melt the landscape, keeping it locally warm for thousands of years." That might make for episodic surface life, or maybe life that toughs it out in spore form until the next warm spell.

And then there’s the possibility that earlier in its history, Titan’s atmosphere was thicker (there’s some evidence for that, notes Jakosky). If so, maybe there was once more of a greenhouse effect – and possibly temperatures salubrious enough to sustain liquid water – and spawn life.

The bottom line is that there’s still no bottom line. The up-close-and-personal photos of Titan’s landscape show rocks and chunks of ice, and nothing that seems to be alive. But quite obviously, that doesn’t rule out Titans, either extant or extinct. If someday we find that this anti-hellish world has spawned even the simplest biology, we could claim more than just some diminutive, solar system neighbors. We would have hard proof that life is no delicate flower, no finicky accident resulting from extraordinary circumstances, but a common fact of the universe.

Dolores Beasley
Headquarters, Washington Feb. 24, 2005

Carolina Martinez
Jet Propulsion Laboratory, Pasadena, Calif.

RELEASE: 05-059

NASA'S CASSINI CONTINUES MAKING NEW SATURN DISCOVERIES

NASA's Cassini spacecraft continues making new and exciting discoveries. The findings include wandering and rubble-pile moons; new and clumpy Saturn rings; splintering storms and a dynamic magnetosphere.

"For the last seven months it has been a nonstop, science-packed mission. It has been a whirlwind, and already we have many new results," said Dr. Dennis Matson, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Weak, linear density waves caused in Saturn's rings by the small moons Atlas and Pan have yielded more reliable calculations of their masses. The masses imply the moons are very porous, perhaps constructed like rubble piles. They are similar to the moons that shepherd Saturn's F ring, Prometheus and Pandora.

Another discovery was a tiny moon, about three miles across, recently named Polydeuces. Polydeuces is a Trojan moon of Dione. They are found near gravitationally stable points, and Saturn is the only planet known to have moons with companion Trojan moons.

The new findings include refinements in the orbits of several of Saturn's small satellites. One intriguing result is the eccentric and slightly inclined orbit of Pan in Saturn's A ring. The orbit's shape is significant, as it indicates the type of interaction the moon has with the ring material surrounding it. If Pan's orbit remains eccentric due to this interaction, then planets growing in a disc of material surrounding a star may also have eccentric orbits. This may help explain the eccentric paths of planets orbiting other stars.

Several faint Saturn rings have been discovered in Cassini images. Some lie in various gaps in the rings and may indicate the presence of tiny embedded moons acting as shepherds. Several of the rings are kinked, likely evidence of nearby moons.

Scientists also found Saturn's winds change with altitude, and small storms emerge out of large ones. For the first time, Cassini images captured possible evidence of processes that may maintain the winds on Saturn. The observations offer a glimpse into the process which transfers energy by convection from Saturn's interior to help sustain strong winds.

Other results improve the understanding of Saturn's complex magnetic environment.
"Saturn's magnetosphere is truly unique. It's dynamically similar to Jupiter's, but in places it chemically resembles water-based plasmas surrounding comets," said Dr. David Young. He is Cassini principal investigator for the plasma spectrometer instrument from the Southwest Research Institute, San Antonio.

Another surprising find was made by the ion and neutral mass spectrometer instrument, which measured molecular oxygen ions above Saturn's ring plane. "This is at first surprising since the rings are made of water ice," said Dr. Hunter Waite, principal investigator for the spectrometer from the University of Michigan, Ann Arbor. "This may have important consequences for the identification of spectral features to use in the search for life on extrasolar terrestrial planet systems," he added.

The abundance of molecular oxygen on Earth is uniquely tied to biology. But these new measurements at Saturn suggest there are lifeless processes associated with cold icy surfaces that may produce an independent pathway for the formation of molecular oxygen in atmospheres. The findings were published in the journal Science.

The Cassini-Huygens mission is a cooperative project of NASA, the European and Italian Space Agencies. For information about the Cassini mission on the Web, visit:

http://www.nasa.gov/cassini

For information about NASA and agency programs on the Web, visit:

http://www.nasa.gov

-end-

* * *

Crater Face: 24 Surface Features Named on Saturn's Moon Phoebe
By Bjorn Carey
Staff Writer
posted: 25 February 2005
11:19 am ET

Twenty-four of the largest craters on Phoebe, the small, retrograde outer moon of Saturn have been assigned names by the International Astronomical Union.

Two image montages of Phoebe, taken in June 2004 on Cassini’s first stop on its tour of Saturn, have been released and show the names and locations of the 24 craters identified by the Cassini imaging team as prominent enough to receive names.

The International Astronomical Union, the international authority for assigning names to planetary surface features, makes use of different naming categories for surface features on each object. That way, when people hear or see a name, they can associate it with the object on which the feature is found. The IAU often start with names associated with the legends involving the being whose name is given to the object itself, then choose an additional category if more names are needed.

This is what happened with Phoebe, a Titan goddess and Apollo’s grandmother in Greek mythology. Since her legend is rather short, there were not enough names for all the features that required them.

"We picked the legend of the Argonauts for Phoebe as it has some resonance with the exploration of the Saturn system by Cassini-Huygens," said Toby Owen, of the University of Hawaii at Manoa. He is the chairman of the International Astronomical Union Outer Solar System Task Group and an interdisciplinary scientist on the Cassini-Huygens mission.

Scrutinizing Saturn: Astronomers Get Best Views Ever

By Bjorn Carey
Staff Writer
posted: 01 March 2005
06:29 am ET

Ever since the Cassini spacecraft began taking pictures of Saturn and its moons last February, scientists have had plenty of work on their plates. Last week several new images and data from the mission were published in the journal Science.

Among the findings is the detection of molecular oxygen around Saturn’s A ring. ( The ring system begins from the inside out in this order: D, C, B, A, F, G, E.)

Molecular oxygen forms when two oxygen atoms bond together. It is rarely seen beyond Earth, where it is created continuously as a byproduct of photosynthesis in plants.

On Saturn, where there is no plant life, molecular oxygen must be formed in a different way -- through a chemical reaction between the Sun’s radiation and the icy particles that comprise Saturn’s rings, scientists said.

Scientists studying radiation in the rings of Saturn also found evidence of oxygen. Doug Hamilton of the University of Maryland said the main radiation belts in the rings are comprised mostly of oxygen and water.

"That is most likely the result of the bombardment of the planet’s rings and icy moons by the radiation trapped in Saturn’s magnetic field," Hamilton said.

Molecular oxygen has also been found above the icy Galilean moons of Jupiter.

Working in coordination with Hamilton’s group, a group of scientists at the Applied Physics Laboratory at Johns Hopkins University found an unexpected radiation belt in the D ring. And they learned that the radiation belts of Saturn are more intense on the night-side of the planet.

Invisible moon?

Images of the narrow Keeler gap in Saturn's A ring offer circumstantial evidence of an unseen moon.

The Keeler gap is narrow, only 26 miles (42 kilometers) wide. Several faint discontinuities, or spikes, in the outer edge of the gap have been discovered and are similar to spikes seen in the core of the inner F ring, which is home to the moon Prometheus.

Based on the similarity to the features caused by Prometheus in the F ring, it is likely that the newly discovered features are the product of the passage of a yet-unseen moonlet on an eccentric orbit within the Keeler gap. The tiny moon would have a diameter of only a few miles. It was first reported last November.

New ring phenomena

An assortment of new ring phenomena was observed on the dark side of Saturn’s rings immediately after Cassini entered orbit. The new ring variations may be evidence of the clumping and aggregation of ring particles, most likely caused by gravitational effects of Saturn or other bodies.

Closer looks at gravitational disturbances in the rings could lead to the discovery of new ring-bound moons.

As the particles comprising the rings orbit Saturn they pass through what are called Pan wakes, wavy features seen in the outer edges of the A ring. They are the result of the tiny moon’s gravitational pull on the particles in this ring.

As the particles orbit through the Pan wakes, they are forced closer together than normal and create a ropy appearance. Similar ropy features seen in other regions of the rings could be evidence of hidden moons.

New rings

Also, several new faint rings have been spotted in new images from Cassini. Many of these are in various gaps between other, larger rings and may indicate the presence of tiny moons, either coincident with the ring or close by. [NASA has a summary here.]

One ring, which was reported earlier, lies in the same orbit as the small moon Atlas.

Porous moons

Other new data from the inner rings has yielded more reliable approximations of the masses of two of Saturn’s ring-bound moons, Atlas and Pan.

The research implies the moons are very porous – similar to moons orbiting just outside Saturn’s rings. The low densities suggest that all the inner moons and satellites were smaller bits and pieces that were gravitationally pulled together; basically orbiting rubble piles.

Trojan moon

Late last year it was reported that researchers had found a new moon orbiting Saturn, but recent findings suggest that it is instead a "Trojan moon."

Trojan moons are companions to larger moons. In this case, the 3-mile-wide (5-kilometer) Polydeuces orbits Saturn in lockstep with the larger moon Dione.

More to come

The deluge of images and data from Cassini will continue for the next three-plus years. Early in March, the orbiter will swing past Enceladus, whose surface is relatively young – 100 million years or so – and has many interesting features.

The ice that coats it is especially clean, and gives the moon the highest albedo, a measure of light reflectivity, of any body in the solar system. Enceladus has an albedo greater than 90 percent, whereas the Earth and its moon have albedos of 38 percent and 12 percent, respectively.

posted: 16 March 2005
03:28 pm ET

This false-color, close-up look at Enceladus yields new insight into the different processes that have shaped the moon’s icy surface. Extending through the center of this image, a system of two-mile (three-kilometer) wide rifts and 12-mile (20-kilometer) wide lanes of grooved terrain separate two distinct geological provinces on Enceladus. To the right of the boundary is older, cratered terrain – a region peppered with craters of all sizes from six miles (10 kilometers) in diameter, down craters near the limit of resolution. Image Credit: NASA/JPL/Space Science Institute

The Cassini spacecraft has revealed that Saturn's icy moon Enceladus has a significant atmosphere.

The spacecraft unlocked the moon’s secret during recent flybys, NASA’s Jet Propulsion Laboratory announced Wednesday. Scientists, using Cassini's magnetometer instrument for their studies, said the source may be volcanism, geysers, or gases escaping from the surface or the interior.

When Cassini had its first encounter with Enceladus on Feb. 17 at an altitude of 725 miles (1,167 km), the magnetometer instrument saw a striking signature in the magnetic field. On March 9, Cassini approached to within 310 miles (500 km) of Enceladus' surface and obtained additional evidence.

The observations showed a bending of the magnetic field, with the magnetospheric plasma being slowed and deflected by the moon. In addition, magnetic field oscillations were observed. These are caused when electrically charged (or ionized) molecules interact with the magnetic field by spiraling around the field line. This interaction creates characteristic oscillations in the magnetic field at frequencies that can be used to identify the molecule. The observations from the Enceladus flybys are believed to be due to ionized water vapor.

"These new results from Cassini may be the first evidence of gases originating either from the surface or possibly from the interior of Enceladus," said Dr. Michele Dougherty, principal investigator for the Cassini magnetometer and professor at Imperial College in London. In 1981, NASA's Voyager spacecraft flew by Enceladus at a distance of 56,000 miles (90,000 km) without detecting an atmosphere. It's possible detection was beyond Voyager's capabilities, or something may have changed since that flyby.

This is the first time since Cassini arrived in orbit around Saturn last summer that an atmosphere has been detected around a moon of Saturn, other than its largest moon, Titan. Enceladus is a relatively small moon. The amount of gravity it exerts is not enough to hold an atmosphere very long. Therefore, at Enceladus, a strong continuous source is required to maintain the atmosphere.

The need for such a strong source leads scientists to consider eruptions, such as volcanoes and geysers. If such eruptions are present, Enceladus would join two other such active moons, Io at Jupiter and Triton at Neptune. "Enceladus could be Saturn's more benign counterpart to Jupiter's dramatic Io," said Dr. Fritz Neubauer, co-investigator for the Cassini magnetometer, and a professor at the University of Cologne in Germany.

Since the Voyager flyby, scientists have suspected that this moon is geologically active and is the source of Saturn's icy E ring. Enceladus is the most reflective object in the solar system, reflecting about 90 percent of the sunlight that hits it. If Enceladus does have ice volcanoes, the high reflectivity of the moon's surface might result from continuous deposition of icy particles originating from the volcanoes.

Enceladus' diameter is about 310 miles (500 km), which would fit in the state of Arizona. Despite its small size, Enceladus exhibits one of the most interesting surfaces of all the icy satellites.

By Christopher Chyba
Carl Sagan Chair for the Study of Life in the Universe; Principal Investigator, NASA Astrobiology Institute team
posted: 14 April 2005
06:43 am ET

For the past year, the SETI Institute has been one of the lead teams in NASA’s Astrobiology Institute (NAI), and this week many members of the SETI Institute have been in Boulder, CO for the biennial meeting of the NAI. The SETI Institute’s team pulls together a dozen of our scientists and educators in Life in the Universe research, SETI research, and Education and Public Outreach to address some of the most important questions in astrobiology. Chief among these is to understand how the origin and evolution of life depends upon particular planetary environments, and how, in turn, planetary environments may themselves be shaped by biology. We are pursuing these questions by investigating a number of worlds in our own solar system, and by asking similar questions about worlds orbiting other stars.

Within our solar system, our work starts with the early Earth. As long as Earth remains the only world on which life is known to exist, astrobiology has little choice but to build on our knowledge of terrestrial biology. We must always be aware that life in other places may have found other ways to make its biology work, but exploring terrestrial life nevertheless gives us the starting point for many of the questions we ask.

Besides Earth, we are paying a great deal of attention to three other worlds in the solar system. (1) Mars, which once clearly had liquid water on its surface, and may still have for at least brief periods. The Red Planet may or may not harbor a subsurface biosphere. (2) Jupiter’s moon Europa, which almost certainly is host to the solar system’s second ocean, with the possibility that that ocean hosts at least microbial life, and (3) Saturn’s moon Titan, the most mysterious of all, and a body that has recently been explored in detail by the Cassini spacecraft and the Huygens probe.

All these investigations will impact our SETI searches, because they will help us understand the kinds of planets and moons—and therefore the kinds of solar systems—that might harbor life. In particular, the Allen Telescope Array (ATA) will soon face the question of whether it should look for artificial signals from worlds orbiting red dwarfs – so-called M stars. Planets orbiting these stars face particular challenges to the possibility of liquid water oceans at their surfaces, and whether or not these worlds or their moons provide good venues for life remains controversial. The SETI Institute’s NAI team pulls together a team of biologists, climate modelers, planetary scientists, astronomers and SETI researchers to examine these issues in detail over a series of workshops. The outcome will determine whether or not the ATA devotes resources to listening for signals from M stars.

The decision is a major one, as M stars comprise some 75% of the stars within the thousand or so light-years to be probed by the ATA. In effect, questions about SETI searches have driven our team to ask questions about planetary habitability. As is so often the case, SETI and other forms of astrobiology reinforce each other in important ways.

Much of our thinking about Mars, Europa and even M-star planets builds on an Earth-based paradigm for life – in particular, on a requirement for liquid water. Titan is the one world we are investigating in detail that in most respects falls outside this usual model. At around –180 C, the surface of Titan is too cold for anything other than occasional transient liquid water environments. But it is of great astrobiological interest nonetheless, for at least two reasons. The first is that the chemistry of its current atmosphere in some ways resembles that thought to have existed in the atmosphere of early Earth. Not only should understanding this chemistry help address important questions related to origins-of-life chemistry on early Earth, but it might even help us understand the reasons why early Earth’s atmosphere slowly became more oxygen-rich over time. Understanding these processes is one of the objectives of the work of Emma Bakes, a Co-Investigator in the SETI team’s NAI project.

The second reason that Titan is of great astrobiological interest is that it appears (we’ll likely know for sure soon) to present us with an example of a world where there is a meteorological cycle based on liquid methane, rather than liquid water. Scientists have long speculated about whether life could be based on some liquid other than water. Life based on liquid hydrocarbons like methane or ethane would have to be extraordinarily different than life based on water; the solution chemistry would be entirely dissimilar to what we know. Such speculations are so difficult to assess that they would never have been sufficient to justify the Titan Huygens probe. But even though we are going to Saturn and Titan for less speculative reasons, the chemistry revealed by the Huygens probe should nevertheless help provide insight into the possibility – or the unlikelihood – of such truly different forms of life.

Carolina Martinez
Jet Propulsion Laboratory, Pasadena, Calif.

Preston Dyches
Space Science Institute, Boulder, Colo.

RELEASE: 05-166

NASA'S CASSINI REVEALS LAKE-LIKE FEATURE ON TITAN

Scientists are fascinated by a dark, lake-like feature recently observed on Saturn's moon Titan. NASA's Cassini spacecraft captured a series of images showing a marking, darker than anything else around it. It is remarkably lake-like, with smooth, shore-like boundaries unlike any seen previously on Titan.

"I'd say this is definitely the best candidate we've seen so far for a liquid hydrocarbon lake on Titan," said Dr. Alfred McEwen, Cassini imaging team member and a professor at the University of Arizona, Tucson. The suspected lake area measures 145 miles long by 45 miles wide, about the size of Lake Ontario, on the U.S. Canadian border.

"This feature is unique in our exploration of Titan so far," said Dr. Elizabeth Turtle, Cassini imaging team associate at the University of Arizona. "Its perimeter is intriguingly reminiscent of the shorelines of lakes on Earth that are smoothed by water erosion and deposition," she added.

The feature lies in Titan's cloudiest region, which is presumably the most likely site of recent methane rainfall. This, coupled with the shore-like smoothness of the feature's perimeter makes it hard for scientists to resist speculation about what might be filling the lake, if it indeed is one.

"It's possible that some of the storms in this region are strong enough to make methane rain that reaches the surface," said Cassini imaging team member Dr. Tony DelGenio of NASA's Goddard Institute for Space Studies in New York.

"Given Titan's cold temperatures, it could take a long time for any liquid methane collecting on the surface to evaporate. So it might not be surprising for a methane-filled lake to persist for a long time," DelGenio added.

Despite earlier predictions, no definitive evidence for open bodies of liquid have been found on Titan. Cassini has not yet been in a favorable position for using its cameras to check for glints from possible surface liquids in the south polar region.

"Eventually, as the seasons change over a few years, the convective clouds may migrate northward to lower latitudes," said DelGenio, "If so, it will be interesting to see whether the Cassini cameras record changes in the appearance of the surface as well," he added.

"An alternate explanation is that this feature was once a lake, but has since dried up, leaving behind dark deposits," Turtle said. Yet another possibility is that the lake is simply a broad depression filled by dark, solid hydrocarbons falling from the atmosphere onto Titan's surface. In this case, the smooth outline might be the result of a process unrelated to rainfall, such as a sinkhole or a volcanic caldera.

"It reminds me of the lava lakes seen on Jupiter's moon, Io," Dr. Torrence Johnson, an imaging team member at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

"It is already clear that whatever this lake-like feature turns out to be, it is only one of many puzzles that Titan will throw at us as we continue our reconnaissance of the surface over the next few years," said Dr. Carolyn Porco, imaging team leader at the Space Science Institute in Boulder, Colo.

Thirty-nine more Titan flybys are planned for Cassini's prime mission. In future flybys the science teams will search for opportunities to observe the lake feature again and to look for mirror-like reflections from smooth surfaces elsewhere on Titan. Such reflections would strongly support the presence of liquids.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the Cassini mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute in Boulder.

To view a computer-enhanced image of the feature and a three-frame movie showing the evolution of nearby clouds on the Internet, visit:

http://www.nasa.gov/cassini

-end-

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07.26.05

NASA's Cassini spacecraft has obtained new, detailed images of the south polar region of Saturn's moon Enceladus. The data reveal distinctive geological features and the most youthful terrain seen on the moon. These findings point to a very complex evolutionary history for Saturn's brightest, whitest satellite.

Image : This dramatic scene from Cassini illustrates an array of processes on Saturn's moon Enceladus, a once geologically active world. Most of the larger craters appear to have softened from their original, presumably crisp appearance, and are cross-cut here by numerous faults. Image credit: NASA/JPL/Space Science Institute.

Cassini's July 14 flyby brought it within 175 kilometers (109 miles) of the surface of the icy moon. The close encounter revealed a landscape near the south pole almost entirely free of impact craters. The area is also littered with house-sized ice boulders carved by unique tectonic patterns found only in this region of the moon.

As white as fresh snow, Enceladus has the most reflective surface in the solar system. Previous Cassini flybys revealed Enceladus, in contrast to Saturn's other icy moons, has lightly cratered regions, fractured plains and wrinkled terrain.

In July, NASA's Cassini spacecraft made its latest flyby of Saturn's moon Enceladus, revealing an unexpected hot spot on the moon's south pole.

The finding flipped everything scientists knew about Enceladus on its head, because what should have been a dead moon appeared to be geologically active and what was supposed to be the moon's coldest region turned out to be its warmest.

"This is as astonishing as if we'd flown past Earth and found that Antarctica was warmer than the Sahara," said John Spencer, an astronomer from the Southwest Research Institute in Colorado and a co-investigator of the Cassini mission.

The finding could explain an old mystery concerning Enceladus, but it also presents a new puzzle of its own....

New View of Titan: Strong Winds, Soft Ground and Lightning
By Bjorn Carey
SPACE.com
posted: 30 November 2005
05:11 pm ET

When the Huygens probe touched down on Titan, it landed on a relatively soft patch of material similar to lightly packed snow, researchers announced today.

But to get to that soft patch, Huygens had to descend through a treacherous atmosphere where winds raged up to 270 mph, temperatures dropped as low as -333 degrees Fahrenheit, and lightning was likely.

Nearly a year after the probe landed on Saturn's largest moon, scientists are still poring over loads of data. Today, researchers released their newest findings in a series of seven reports published on line by the journal Nature.

The findings provide a better picture of some of the most basic characteristics of Titan, a smog-shrouded world that had eluded close scrutiny until Huygens and the Cassini mothership teamed up for a series of observations.

The landing site

Titan's surface was unveiled as Huygens plunged through the clouds and fired up its Descent Imager/Spectral Radiometer (DISR). While these images did not show the pools of liquid hydrocarbon that many scientists expected, they do show the signs of flowing liquid in the form of brightness variations around the outlines of "ponds" and a "coastline" as well as what appear to be slopes carved by liquid drainage.

Images taken after landing show several small stones and pebbles and that the general topography of the region is fairly flat, varying only 3 feet or so in height. Images and other instruments ruled out the presence of extensive methane ground fogs in the landing site.

The surface of the landing site was neither hard nor fluffy soft, instead having characteristics similar to wet clay, lightly packed snow, or wet or dry sand, into which the probe sank a tiny bit after landing. The composition of surface vapors near the probe showed that the surface was wet with methane, which evaporated as the warm probe landed in the cold soil. The surface was also rich in organic compounds – such as cyanogen and ethane – not detected in the atmosphere.

Some scientists speculated that a tide had just gone out and the probe landed on the still-wet beach.

Super-windy

Scientists had long suspected that Titan's atmosphere was moving around the planet faster than the planet was rotating – a physical characteristic known as superrotation and previously observed on Venus. Now, data from the probe's DISR instrument and the Doppler Wind Experiment have confirmed that Titan's methane filled clouds do indeed superrotate.

While the uppermost clouds – about 75 miles above the surface – spin around the planet at about 270 miles per hour, wind speeds gradually decline as the near the surface. Here generally weak winds, gusting no more than a few feet per second, were observed in the lowest 3 miles of the probe's descent.

The probe passed through one other region of near zero wind speeds, from altitudes 62 to 37 miles. Scientists cannot explain this yet.

Atmosphere

During its descent, Huygens provided the first in situ look at what chemicals exist in Titan's atmosphere. The atmosphere is mainly nitrogen and methane, but scientists didn't know how these chemicals originated – did they arrive in their present form or were they originally part of other molecules and were chemically altered to the states seen today.

The gas argon 36 was detected by the Gas Chromatograph Mass Spectrometer in very low abundance, and scientists say this indicates that nitrogen was originally present as part of ammonia. Also, the early atmosphere of the planet was at least five times denser with nitrogen than it is now, suggesting that some of the gas has been lost into space.

Ratios of carbon isotopes also indicate that the atmosphere is also leaking methane, and that there must be some period method for replenishment, although none was observed. Some researchers predicted there would be a large methane surface or subsurface reservoir that replenished the atmosphere, although that too was not seen. Also missing from the observations was the signs of methane rain, which scientists believed showered the planet's surface.

It could be that cyrovolcanoes – similar to terrestrial volcanoes except they spew liquid water and ammonia from subsurface reservoirs – could be providing both the atmosphere and the surface with nitrogen and methane.

"The current theories are that there is a region of water-ammonia mix in liquid form at some depth below Titan's surface – this is equivalent to the magma on Earth," study co-author Andrew Ball told SPACE.com. "These are one possible source for renewable methane on Titan."

Aerosol clumps, freezing temperatures, and maybe some lightning

The Aerosol Collector and Pyrolyser (ACP) instrument analyzed particles as it passed through the clouds and reported the presence of nitrogen-containing organic compounds, which may include amino, imino, and nitrile groups – key components to protein formation here on Earth.

These particles also clump together, perhaps providing a foundation for cloud formation, and affect temperatures and wind speeds throughout the atmosphere. They also fall as kind of steady organic rain on Titan's surface, the researchers write, and could produce a global blanket with a potential thickness of half a mile or more.

Researchers also used the Huygens Atmospheric Structure Instrument (HASI) during the descent to measure the atmosphere's temperature from the upper layers all the way down to the surface. Temperature at the surface averaged around -289 degrees Fahrenheit, which is warm enough for the existence of lakes and rivers of liquid natural gas. Atmospheric temperatures ranged from -333 degrees Fahrenheit at the highest elevations – 870 miles above the surface – to about -154 degrees Fahrenheit in the stratosphere, about 25 miles from the surface.

The HASI instrument also detected electric activity that is similar to lightning's signature. This was spotted around 37 miles above the planet's surface, which is also the region where the wind speed dropped to near zero.

This story was updated at 2:52 p.m. EST.

Saturn’s moon Enceladus may have pockets of liquid water lurking beneath its surface, feeding great jets that spew from the satellite and hinting at the possibility of a habitable environment, researchers said Thursday.

Observations from the Cassini spacecraft currently studying Saturn and its myriad moons shows Enceladus, one of the brightest objects in the Solar System, to be a geologist’s dream, with an active plume spewing water and other material spaceward, as well as a hot spot of thermal activity at its south pole.

"This finding has substantially broadened the range of environments in the solar system that might support living organisms, and it doesn't get any more significant than that," said Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colorado, in an e-mail interview. "I'd say we've just hit the ball right out of the park."

Porco led one of nine studies of Enceladus, all of which are detailed in this week’s issue of the journal Science, based on Cassini’s observations from three flybys past the moon – each closer than the last – in February, March and July of 2005.

Enceladus’ active nature points toward subsurface water reservoirs beneath its icy exterior, much like that believed to churn just under the surface of Jupiter’s moon Europa, researchers said. But unlike Europa, which researchers believe harbors a vast ocean beneath kilometers of thick ice, Enceladus’ water may be just below the surface.

"What’s different here is that pockets of liquid water may no more than tens of meters below the surface," said Andrew Ingersoll, a Cassini imaging team member and atmospheric scientist at the California Institute of Technology, in a statement.

Plume science

Cassini caught hard evidence of Enceladus’ plume since last year, though scientists were unsure of what powers the jets of particles blowing into space. The moon is only the third other body in the Solar System – Earth, Jupiter’s moon Io and possibly Neptune’s moon Triton are the others – known to have active volcanic processes, researchers said.

Porco’s team found evidence that the jets may erupt from buried pockets of water at temperatures above 32 degrees Fahrenheit (0 degrees Celsius) like a frigid geyser.

The close proximity of water, rock and the south pole’s thermal hot spot puts Enceladus on the list of possible harbors for biological activity, some researchers said.

"You’ve got liquid water, and it’s liquid water interfacing with rock…and there’s energy," NASA Cassini scientist Candice Hansen-Koharcheck told SPACE.com. "We’ve got the very most basic ingredients here, and so that notches it up on the biological potential list."

Cassini’s instruments could help pin down Enceladus’ liquid water sources in future passes, researchers added.

"If a wet domain exists at the bottom of Enceladus’ icy crust, Cassini may help to confirm it," writes Jeffrey Kargel, a research scientist with the University of Arizona’s Department of Hydrology and Water Resources, in a related article in Science.

But the spacecraft, Kargel wrote, will not be able to determine whether subsurface water pockets could offer a habitat suitable for living organisms.

"Any life that existed could not be luxuriant and would have to deal with low temperatures, feeble metabolic energy, and perhaps a severe chemical environment," Kargel wrote. "Nevertheless, we cannot discount the possibility that Enceladus may be life’s distant outpost."

Other mysteries

Cassini’s Enceladus flybys also answered other questions surrounding the role of the moon’s plume in the near-Saturn environment.

The plume, which a team of researchers led by Hansen-Koharcheck at the Jet Propulsion Laboratory in Pasadena, California believe may have been erupting continuously for 15 years, appears to replenish Saturn’s E-ring with material and provide the source of oxygen and hydrogen permeating the planet’s neighborhood.

"It’s definitely the water, there’s no doubt about it," Hansen-Koharcheck said, adding that trace amounts of other materials are also present in the plume.

Cassini deputy project scientist Linda Spilker told SPACE.com that the plume activity on Enceladus is much different from the volcanoes on Jupiter’s moon Io, where material eventually settles back on the surface once it erupts. Instead, Enceladus spews material directly into space and Saturn’s E-ring.

"If you turned Enceladus off, you would probably turn off the E-ring," Spilker added.

The plume’s activity appears tied to the thermal hotspot at Enceladus’ south pole, the source of that internal heat remains undetermined.

"We think we can rule out a radioactive related source," said John Spencer, a Cassini scientist with the Southwest Research Institute in Boulder, adding that tidal heating from the gravitational pull of nearby Saturn is a more likely culprit.

Cassini’s next chance to take a close look at Enceladus will occur in 2008, when the probe will swing within 220 miles (350 kilometers) of the small moon, though the probe may have a few long-distance views before then, researchers said.

"We’re all going to have to patiently wait," Hansen-Koharcheck said.

BOULDER, Colorado—The discovery of apparent liquid water reservoirs erupting in Yellowstone-like geysers on Saturn’s moon Enceladus has produced a gusher of questions.

One leading unknown to solve: Could liquid water residing within a body so small and so cold provide comfort-level conditions suitable for living organisms?

NASA announced last month that high-resolution Cassini images of Enceladus show icy jets and lofty plumes that expel large quantities of particles at high speed. Scientists think the jets spout from near-surface pockets of liquid water, super-cold versions of the Old Faithful geyser in Yellowstone.

In the spring of 2008, Cassini is slated for another chance to look at Enceladus, flying within some 220 miles (350 kilometers) of the perplexing moon. The end of Cassini’s "Prime Mission" is June 30, 2008, four years after arrival at Saturn.

The opportunity exists for placing Cassini in "extended mission" mode—but that’s only if financial resources allow.

Fueled by the spacecraft’s findings to date, attention is now turning to future observational roles of the interplanetary probe. One leading candidate is a sharper focus on astrobiology—even a "diving catch" to inspect in detail the makeup of those Enceladus plumes.

Cardinal goal

"After what we’ve discovered with Cassini, if we don’t get an extended mission, then there’s no hope for anybody," said Carolyn Porco, the Cassini imaging team leader based here at the Space Science Institute. The Cassini Imaging Central Laboratory for Operations (CICLOPS) is the nerve center for the imaging team of the Cassini mission to Saturn.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.

Cassini scientists should know a year from now whether or not Cassini will be given official approval for an extended mission. Then, within six months to a year after that, they will learn if the money is available to proceed beyond the nominal end of the mission, in mid-2008.

"In the meantime, we are planning for such an extension ... thinking about what it is we really want and need to do," Porco told SPACE.com. "Certainly, one of the cardinal goals of extending Cassini’s tour of the Saturnian environment would be further exploration of Enceladus," she said.

Microbes in the mix

Porco said Enceladus’ interior structure would be determined with close flybys designed to allow for such measurements.

"We would aim to fly very close over the south pole [of the moon] and through the jets and plume," Porco said, "in order to make more accurate measurements of the composition of the vapor and ice particles." Of course, how close Cassini can get to this action from Enceladus will be ultimately determined by spacecraft safety issues ... "but that would be the goal," she said.

And what about looking for microbes mixed in with those high-flying plumes?

"It’s not clear that Cassini has the means to determine if the ice crystals themselves contain microbes," Porco explained. "It may require a device with much greater compositional precision than we have, so that may have to be left for a future mission."

Sounds like a winner

In charting out further study of Enceladus, Porco said they would also want to refine their remote sensing measurements. They would map the thermal radiation emerging from the south polar region in much greater detail, to see exactly where the warmest places are on the Saturnian moon.

"We will want to do a better job of determining the composition of the ices comprising the fractures, which contain the simplest organic compounds not found anywhere else," Porco continued. "And we will want to take higher resolution images of the jets to refine our estimates of particle abundance and size, and ascertain in which locales the most vigorous geysers are occurring."

In short, Porco said, "Cassini is so very well equipped, that it could be the precursor mission for a future landed mission to the south pole of Enceladus. In other words, we could do in the next few years with Cassini at Enceladus what the next orbiter of Jupiter would do at Europa."

Unlike Jupiter’s Europa, Enceladus has no intense radiation field that can limit the available time for spacecraft operations. "So, water closer to the surface and more time spent conducting scientific investigations....sounds like a winner to me," Porco said.

Well-instrumented flagship

"It is very important for future missions to Titan and Enceladus that Cassini gather as much information as possible on these bodies," said Jonathan Lunine, Professor of Planetary Sciences and of Physics at the University of Arizona in Tucson.

Exciting new discoveries will be made, and it will be possible to advance significantly the planning of possible future missions to Titan and Enceladus on the basis of what is learned from Cassini, Lunine told SPACE.com. "One could even imagine an extended mission with enough emphasis on Titan and Enceladus," he said, "to constitute a kind of ‘Cassini Astrobiology Mission’".

During last month’s 37th Lunar and Planetary Science Conference (LPSC) in Houston, Texas, Lunine also underscored another realization stemming from Cassini’s take on Enceladus.

"One of the lessons about this is that we cannot explore the outer solar system without well-instrumented flagship missions," Lunine told the LPSC gathering. Given Cassini’s range of science gear, the nature of an Enceladus-spewing plume can be studied, as can the mechanisms that form a plume, he said.

"It’s possible, but not certain, by the end of the [Cassini] mission that there will be a more definitive answer as to whether the plume geyser activity requires liquid water in the Enceladus subsurface," Lunine suggested.

Key target

There’s a trio of reasons why Enceladus is very interesting for astrobiology, said Chris McKay, a planetary scientist at the NASA Ames Research Center, Moffett Field, California.

The moon’s activity suggests that there must be some sort of subsurface energy source, possibly gravitational tidal effects, McKay told SPACE.com, and that this energy source is concentrated and not a global diffuse heating. This may imply liquid water below the surface, he said.

A concentrated energy source, liquid water, and perhaps evidence of CH4—methane—being seen, McKay added it up this way: "All together this makes Enceladus a key target for astrobiology. Let’s go."

What additional can Cassini do?

McKay said that further observations of the plume and more detailed measurements of the dust coming from the plume would be ideal. "Key would be the detection of carbon and nitrogen containing particles," he added.

Best place to go?

While the scientist avoids rating Enceladus to Mars and Europa—other targets of keen astrobiology interest—McKay noted: "But clearly the Saturn system with organic rich Titan and water-active Enceladus is on the first rank of targets for astrobiology. We should start planning a combined Enceladus lander and Titan balloon mission."

Carolyn Porco explained that, in her mind, if the goal is to get up close and personal with extraterrestrial bodies of liquid water, then Enceladus appears to be at the moment the best place to go.

"It has liquid water, two-and-a-half times more heat coming out of the south polar region, per square meter, than the Earth, and simple organics," Porco concluded.

"It’s quite provocative, and is looking very good from the astrobiological point of view."

Recent images of Titan, Saturn's largest moon, bear a striking resemblance to some of the deserts on Earth.

The pictures, captured by the Cassini spacecraft as it flew by Titan last October and released today, show sand dunes at Titan's equator much like those in the Sahara desert.

"It's bizarre," said Ralph Lorenz of University of Arizona's Lunar and Planetary Laboratory. "These images from a moon of Saturn look just like radar images of Namibia or Arabia."

On Earth, all wind is ultimately a result of heat differences produced by sunlight that warms the planet unevenly. Scientists have long assumed Titan is too far from the Sun to have solar-driven surface winds powerful enough to cause sand dunes.

But they have more recently learned that Saturn's powerful gravity creates tidal effects in Titan's thick atmosphere. This tidal force, almost 400 times greater than that of Earth's moon tugging at our oceans, dominates near surface winds on Titan and sculpts dunes that are up to 330 feet high.

Rows of sand

The new images, revealed in the May 5 issue of the journal Science, are evidence that these dunes were built from winds that blow in one direction before switching to another and then back to the first direction and so on.

The tides cause wind to change direction as they drive winds toward the equator, Lorenz said.

This back and forth pattern cause the sand dunes to build up in long parallel lines.

These tidal winds combined with Titan's west-to-east zonal winds create dunes aligned nearly west-to-east everywhere except close to mountains, which alter wind direction.

Scientists also thought that the dark regions on Titan's equator were in fact seas of liquid ethane that trap sand. But the images reveal something different.

"If you look at the dunes, you see tidal winds might be blowing sand around the moon several times and working it into dunes at the equator," Lorenz said. "It's possible that tidal winds are carrying dark sediments from higher latitudes to the equator, forming Titan's dark belt."

Sand formation

The sand on Titan might have formed when liquid methane rained and eroded the ice bedrock.

Although it doesn't rain frequently on Titan, when it does rain it really pours. Energetic rain that triggers flash floods may be a mechanism for making sand, Lorenz said.

The sand could also have come from organic solids produced by photochemical reactions in Titan's atmosphere.

"It's exciting that the radar, which is mainly to study the surface of Titan, is telling us so much about how winds on Titan work," Lorenz said. "This will be important information for when we return to Titan in the future, perhaps with a balloon."

Saturn's moon Enceladus might have rolled over on its side sometime in the past, a suggestion that would account for a strange finding made by the Cassini spacecraft.

The moon has a hot spot at its south pole, an area of low density where water vapor shoots into space, Cassini discovered. Heat from within is likely created by the varying tugs of Saturn’s gravity as Enceladus' distance from the giant planet changes during the course of its orbit.

Saturn's moon Enceladus backlit by the Sun show the fountain-like sources of the fine spray of material that towers over the south polar region. The image is greatly enhanced and colorized. Credit: NASA/JPL/Space Science Insti

But why is there a hot spot only at the south pole?

"When we saw the Cassini results, we were surprised that this hot spot was located at the pole," said Francis Nimmo of the University of California, Santa Cruz. "So we set out to explain how it could end up at the pole if it didn't start there."

Remember Weebles? They wobble but the don't fall down? A similar imbalance seems to have caused Enceladus' cosmic flop, but with a twist.

in the June 1 issue of the journal Nature, Nimmo and colleagues explain that hot material from within Enceladus welled up in one location. Hot material expands and is less dense.

Like all rotating bodies, the moon would be more stable if low-density areas were at the poles and regions of high density were at the equator. So the moon reoriented itself in that manner, the thinking goes.

There is a way to possibly confirm that the moon flipped. Its former leading hemisphere should have had more impact craters than the trailing hemisphere. If it flipped 90 degrees, the pattern of craters now present would reveal as much.

Patch of Saturn's Moon Resembles Earth

SPACE.com Staff
posted: 19 July 2006
04:47 pm ET

A network of river channels is located atop Xanadu, the continent-sized region on Saturn's moon Titan. This radar image was captured by the Cassini Radar Mapper on April 30, 2006. Credit: NASA/JPL

New radar images of Saturn's moon Titan reveal dunes, hills, valleys and rivers that scientist say look a lot like home.

But on Titan, which is frigid and shrouded in smog, the features are likely carved in ice rather than solid ground.

The detailed view is of a bright area on Titan called Xanadu. It's about the size of Australia and has been studied from afar for years. Now scientists are getting a better look with NASA's Cassini spacecraft. Radar is bounced off the surface to generate an image that cannot be made using visible-light observations because the orbiting spacecraft can't see through the moon's thick atmosphere.

The observations reveal mountains about as high as the Appalachians.

"Surprisingly, this cold, faraway region has geological features remarkably like Earth," said Jonathan Lunine, a Cassini researcher at the University of Arizona.

The river channels are likely carved by liquid methane or ethane, as the moon is too cold for water to be liquid.

"Although Titan gets far less sunlight and is much smaller and colder than Earth, Xanadu is no longer just a mere bright spot, but a land where rivers flow down to a sunless sea," Lunine said.

Liquid methane might fall as rain or trickle from springs to create the rivers, Lunine and his colleagues figure. Perhaps the rivers carry grains of material that accumulate as dunes elsewhere.

"This land is heavily tortured, convoluted and filled with hills and mountains," said Steve Wall, the Cassini radar team's deputy leader at NASA's Jet Propulsion Laboratory. "Xanadu has been washed clean. What is left underneath looks like very porous water ice, maybe filled with caverns."

Evidence of Hydrocarbon Lakes on Titan
By Alicia Chang
Associated Press
posted: 25 July 2006
09:31 am ET

LOS ANGELES (AP) -- Scientists said Monday they have found the first widespread evidence of giant hydrocarbon lakes on the surface of Saturn's planet-size moon Titan.

The cluster of lakes was spotted near Titan's frigid north pole during a weekend flyby by the international Cassini spacecraft, which flew within 590 miles of the moon.

Researchers counted about a dozen lakes six to 62 miles wide. Some, which appeared as dark patches in radar images, were connected by channels, while others had tributaries flowing into them. Several were dried up, but the ones that contained liquid were most likely a mix of methane and ethane.

"It was a real potpourri," said Cassini scientist Jonathan Lunine of the University of Arizona.

Titan is one of two moons in the solar system known to possess a significant atmosphere similar to that of primordial Earth. But scientists have long puzzled over the source of its hazy atmosphere rich in nitrogen and methane.

Scientists believe methane gas breaks up in Titan's atmosphere and forms smog clouds that rain methane down to the surface. But the source of methane inside the moon, which releases the gas into the atmosphere, is still unknown, Lunine said.

Last year, Cassini found what appeared to be a liquid hydrocarbon lake about the size of Lake Ontario on Titan's south pole. But the recent flyby marked the first time the spacecraft spied a multitude of lakes.

Cassini's next Titan encounter will be Sept. 7, when it will be 620 miles away.

Cassini, funded by NASA and the European and Italian space agencies, was launched in 1997 and took seven years to reach Saturn to explore the ringed planet and its many moons. The mission is managed by NASA's Jet Propulsion Laboratory in Pasadena.

Cassini's accompanying probe, Huygens, developed and controlled by the ESA, touched down on Titan in 2005.

Saturn's Moon Titan a World of Rivers and Lakes
By Ker Than
Staff Writer
posted: 03 January 2007
01:01 pm ET

Images shot last summer by NASA's Cassini spacecraft provide the strongest evidence yet that Titan, a saturnian moon and one of the most Earth-like celestial bodies in the solar system, is dotted with a multitude of liquid lakes.

A false-color image of Titan's surface snapped by NASA's Cassini spacecraft on July 22, 2006. The lakes appear darker than the surrounding terrain because of the unique way they scatter radar, which is similar to how water lakes on Earth do it. Credit: NASA/JPL/USGS

"At the time we first announced it, we were like, 'Well, we think these are probably lakes,’ but that was about our level of confidence," said study team member Ellen Stofan of University College London and Caltech. "I would say at this point, we've analyzed the data to the extent that we feel very confident that they are liquid-filled lakes."

Instead of water, however, the Titan lakes [image] are likely filled with methane, and possibly even ethane, organic compounds that are gases on Earth but liquid on the frigid surface of Titan.

"It's going to behave like water," Stofan said about liquid methane. "It's transparent just the way water is. So if you were standing by the shoreline, you would be able to see down to whatever pebbles or gunk that was on the bottom."

Titan is the only moon in the solar system to have a dense atmosphere with thin layers of methane and nitrogen clouds—a setup similar to that of early Earth. Atmospheric methane is destroyed by sunlight over time and must constantly be renewed. Scientists thus speculated that lakes or even oceans of methane might exist on, or just beneath, the moon's icy surface and that evaporation from these liquid bodies was replenishing the atmosphere. The first confirmation of this thinking came last July when Cassini's radar spotted more than 75 large, dark patches around the surface of the moon's northern pole.

"The lakes are basically black in the [radar] data, which is how a liquid would behave," Stofan said. Radar data alone wasn't enough, however. A very smooth deposit of fine soil would also appear black on radar, Stofan explained.

The clincher that the patches were liquid lakes came from looking at the surrounding terrain. Some of the patches appeared to be fed by sinuous channels, or "rivers," some more than 62 miles (100 kilometers) long. Others appeared to be contained within rimmed circular depressions, similar to crater lakes or volcanic calderas on Earth.

"The morphological evidence points completely away from it being a smooth deposit of soil or sediment. It's just not consistent," Stofan said. "Combining these two sets of data, it led us to feel very confident about the interpretation that they're actually liquid."

In a study published in the Jan. 4 issue of the journal Nature, the researchers also suggest that the rivers and lakes are being filled by rainfall from methane clouds or by seepage from beneath the moon's surface.

"You can think of all the exotic words you want to call it—a 'methanofer' because it's not an aquifer. It's a subsurface methane table and not a water table," Stofan told SPACE.com.

The researchers predict that as the seasons progress, lakes in the winter hemisphere should expand while those in the summer hemisphere should shrink or dry up entirely.

Cassini is slated to perform 22 more Titan flybys, the next of which is scheduled for later this month.