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Titan (Saturn's Largest Moon)

Titan probe's pebble 'bash-down'


An ice pebble was almost certainly the first thing the Huygens probe struck as it landed on Titan.

Open University scientists have been running experiments to try to simulate the data returned by a spike that protruded from the lander's underside.

This penetrometer was the first part of Huygens to touch the Saturnian moon and drove about 10cm into the surface.

More than 100 tests by the team have now provided the clearest indication of what that material might be.

Martin Towner and John Zarnecki presented some of the OU's findings here at the UK National Astronomy Meeting.

In the immediate hours and days after the landing, the researchers spoke of Huygens hitting a surface that had a thin crust with a softer, uniform material underneath - something akin to crème brûlée, was the humorous analogy used.

"A crust is still a possibility, but we now think it's most likely we hit one of those water-ice pebbles you see in the ground image; the biggest you see is about 15cm," Professor Zarnecki told the BBC News website.

"We probably pushed the pebble to one side and then ploughed into the stuff underneath which we are pretty convinced is a 'sand' made of ice," the principal investigator on the Huygens surface science package explained.

The OU has a test rig at its Milton Keynes base where an exact copy of the penetrometer can be dropped into a variety of materials to simulate the mechanical properties of Titan's surface.

Glass beads of different sizes have been put in the rig, as well as a range sands and gravels. The penetrometer strikes the test sample at roughly 4-5 m/s, producing a signal that can be matched to the real data returned by Huygens.

Some of the drops have been done at angles to cover the likelihood that Huygens was swinging from side to side under its parachute as it came down.

The results favour a pebble impact.

"A crust and a pebble will give you an initial peak but the match looks better with a pebble and if we're seeing lots of them in the ground image it's hardly fanciful that we've bashed one of them," Professor Zarnecki said.

The sand and gravel Huygens landed in - ranging in size up to 8mm - is not the eroded silicate material one finds on Earth, but water-ice particles mixed with a significant amount of hydrocarbon ice.

The surface temperature gets down to as low as about -180C.

And all this fits with the picture that is emerging of a moon which probably experiences methane rain that runs in channels and rivers, with this fluid flow then depositing "silt" downstream.

"If liquid flows through a solid, it erodes the surface away. If that's made of ice then we'll get ice-sand deposited in the lowlands and that's what we've hit," Professor Zarnecki said.

Future work by the OU team will look at whether the sand is "wet" or gooey because it still holds the rain.

And what of the crème brûlée analogy? Yes, the OU team has tested it.

"I have to stress this was the students; it was all their idea and they did it in their spare time, not in the university's time," Professor Zarnecki admitted.

"They did a drop into a crème brûlée. It had a nice crust and, horrifyingly, they got a signal that wasn't a million miles from the real one from Titan. So maybe the moon is a crème brûlée in the sky after all," the researcher joked.

Huygens landed on Titan, the largest moon of Saturn, on 14 January.

The robotic lab was the major European component in the joint US-Europe Cassini mission that is spending four years investigating Saturn and its satellites.

The Royal Astronomical Society's National Astronomy Meeting has been held at the University of Birmingham.

http://news.bbc.co.uk/1/hi/sci/tech/4417503.stm
 
Cassini scoops complex organics in Titan flyby



The Cassini spacecraft has flown through the upper atmosphere of Saturn's giant moon, Titan, and detected a huge number of complex organic chemicals. Scientists believe that similar processes may have built organic molecules in the atmosphere of early Earth.

Cassini’s closest encounter with Titan so far came on 16 April, as it skimmed within about 1000 kilometres of the moon's surface. During the flyby, an instrument called the Ion and Neutral Mass Spectrometer captured and analysed gases from the upper atmosphere. INMS uses a beam of electrons to ionise these gases before subjecting them to electric fields to measure the telltale atomic mass of different molecules.

Some complex organic molecules - such as benzene and diacetylene - had already been picked up on an earlier approach to Titan, but the latest encounter has yielded an even wider range.

It includes nitriles and scores of different hydrocarbons, some with up to seven carbon atoms. And the results suggest that Titan's upper atmosphere holds even heavier and more complex organics, which are beyond the instrument's mass range.

Reactive radicals
The INMS team were not expecting to find such a rich soup of chemicals so high up - it is something of a mystery why these heavy molecules do not rapidly condense in Titan's cold atmosphere and rain down to the surface.

Scientists do have some idea about how they are formed, however. Methane and molecular nitrogen are thought to be smashed apart by ultraviolet radiation from the Sun and by high energy particles trapped in Saturn's magnetic field. That creates highly reactive radicals that can combine to form more complex molecules.

Similar processes might have operated on the Earth a few hundred million years after it formed, generating the raw materials for life. On the other hand, Earth's organics may have been created in deep space and then delivered by comets.

The Huygens probe - which landed on Titan in January after hitching a ride with Cassini - had previously taken gas readings as it plummeted through the atmosphere, but only began those measurements as it fell beyond an altitude of 150 km.

The Cassini team are hoping to learn more about Titan's atmosphere over the next few years - at least 39 further flybys are planned.

http://www.newscientist.com/article.ns?id=dn7308
 
new picture


Cassini makes detailed ring map


The Cassini probe has obtained the most detailed view yet of Saturn's ring system, making clear even a ring that had eluded previous space missions.

By passing radio waves through the rings, the spacecraft was able to measure the size of the ice and rock fragments from which they are made.

The denser the material in the rings, the weaker the radio signal received from Cassini back on Earth.

The joint US-European mission has been in orbit around Saturn since last July.

Ring tone

This was Cassini's first so-called radio occultation observation of Saturn's rings, atmosphere and ionosphere - meaning that Cassini made the study as it passed behind the rings as seen from Earth. It took place on 3 May.

The observation involved the transmission through the rings of three radio signals of different frequencies. The signals were picked up on Earth by the US space agency's (Nasa) Deep Space Network.

Ring particles of assorted sizes were seen to affect each tone in a different way.

The Cassini mission was designed to optimise the geometry of the first radio occultation experiment and seven further occultations scheduled from May to September 2005. During its lifetime, Cassini will obtain a total of 20 radio occultations of the rings.

Saturn's rings are enormous structures. From edge to edge, they would not even fit in the distance between Earth and the Moon. The seven main rings are labelled in the order they were discovered. From the planet outward, they are D, C, B, A, F, G and E.

"All ring features appear to be populated by a broad range of particle sizes that extend to many metres in diameter at the upper end," said Dr Essam Marouf, Cassini radio science team member.

Marouf said, at the lower end, particles of about 5cm in diameter or less seemed to be scarce in ring B and inner ring A. However, in ring C and outer ring A, particles of less than about 5cm in diameter seem to be abundant.

'Marvellous array'

During the radio observation, Cassini discovered that the inner and outer parts of ring B contain internal rings that are hundreds of kilometres wide and vary greatly in the amount of material they contain.

A thick, 5,000km-wide core of ring B contains several bands with ring material nearly four times as dense as that of ring A, and nearly 20 times as dense as that of ring C.

The dramatically varying structure of ring B is in sharp contrast to the relatively flat structure of ring A or the gentle, wavy structure of ring C, where many dense, narrow and sharp-edged ringlets permeate its outer part.

Cassini also detected more than 40 rippled features called "density waves" in ring A, many near its outer region, close to the moons that orbit just outside the ring.

"A marvellous array of waves, caused by gravitational interactions with nearby moons, has been uncovered throughout ring A," said Marouf.

"We also see a major density wave in the dense ring B. Some of these waves have been seen in Voyager and other Cassini observations, but not in this large number and not with this exceptional clarity."

http://news.bbc.co.uk/1/hi/sci/tech/4574239.stm
 
Hydrocarbon volcano discovered on Titan


A giant methane-spewing volcano has been spotted in close-up images of Saturn's giant moon Titan. But the Cassini and Huygens spacecraft failed to find any signs of the expected oceans or lakes of liquid methane.

The infrared images, which penetrate the perpetual deep smog of Titan, reveal the first clear signs of an unusual kind of ice volcanism. A large dome-like structure 30 kilometres across may be a “cryo-volcano” produced by an upwelling plume of hydrocarbons ices.

The energy source powering such a volcano would be tidal heating of material on the moon, produced by gravitational interaction with Saturn.

Such low-temperature volcanism could be a significant source of methane in the atmosphere of Titan, according to Christophe Sotin, at the University of Nantes in France, and his colleagues.

Dry as a bone
Before the Cassini mission, the presence of methane in Titan's thick atmosphere was taken as evidence that there must be oceans of liquid methane. That is because methane breaks down within 10 million years on Titan and so a source is needed to replenish it.

Cassini flyby images and those taken during the Huygens probe's descent to the surface do show low, dark plains and apparently raised, light regions. They also show some river-like, dark, linear features connecting to the dark regions.

But there are no reflections of the kind that would be expected from liquid surfaces, so oceans or even large lakes of methane are now virtually ruled out.

There are also dark river-like channels on the flanks of the newly found dome structure. The team suggests that while it is clear there are no large bodies of liquid on Titan today, there may have been episodes of methane rain following major volcanic eruptions of methane into the air. But because of methane's short lifetime, they say, these channels would have quickly dried out.

http://www.newscientist.com/article.ns?id=dn7489
 
Titan dark spot may be large lake


A dark, lake-like feature on Saturn's largest moon, Titan, has been imaged by the US-European Cassini spacecraft.
Researchers have long speculated that Titan might harbour open bodies of liquid methane - and the 235km by 75km target is the best candidate to date.

But they are being cautious about interpreting the feature that has what looks to be a smooth shoreline.

The scientists say the object could simply be dark, solid deposits caught in a sinkhole of volcanic caldera.

"This feature is unique in our exploration of Titan so far," said Dr Elizabeth Turtle, Cassini imaging team associate at the University of Arizona, US.

"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.

"An alternate explanation is that this feature was once a lake, but has since dried up, leaving behind dark deposits," Turtle said.

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

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.


http://news.bbc.co.uk/1/hi/sci/tech/4633043.stm
 
Does anybody else (upon looking at the Titan photographs) think that the lakes, rivers and clouds look like craters, cracks and snow topped mountains?

:confused:
 
methane-producing microbes?


Has Huygens found life on Titan?


IF LIFE exists on Titan, Saturn's biggest moon, we could soon know about it - as long as it's the methane-spewing variety. The chemical signature of microbial life could be hidden in readings taken by the European Space Agency's Huygens probe when it landed on Titan in January.

Titan's atmosphere is about 5 per cent methane, and Chris McKay of NASA's Ames Research Center in Moffet Field, California, thinks that some of it could be coming from methanogens, or methane-producing microbes. Now he and Heather Smith of the International Space University in Strasbourg, France, have worked out the likely diet of such organisms on Titan.

They think the microbes would breathe hydrogen rather than oxygen, and eat organic molecules drifting down from the upper atmosphere. They considered three available substances: acetylene, ethane and more complex organic gunk known as tholins. Ethane and tholins turn out to provide little more than the minimum energy requirements of methanogenic bacteria on Earth. The more tempting high-calorie option is acetylene, yielding six times as much energy per mole as either ethane or tholins.

McKay and Smith calculate that if methanogens are thriving on Titan, their breathing would deplete hydrogen levels near the surface to one-thousandth that of the rest of the atmosphere. Detecting this difference would be striking evidence for life, because no known non-biological process on Titan could affect hydrogen concentrations as much.

One hope for testing their idea rests with the data from an instrument on Huygens called the GCMS, which recorded Titan's chemical make-up as the probe descended. It will take time to analyse the raw data, partly because hydrogen's signal will have to be separated from those of other molecules. "Eventually, I hope, we will have numbers for at least upper limits for hydrogen," says Hasso Niemann of Goddard Space Flight Center in Maryland, principal investigator of the GCMS.

Acetylene could be easier to analyse, McKay says, and it too might betray life. "I would guess that there would be a similar fall-off of acetylene if the microbes are eating it." The work is to be published in the journal Icarus.

http://www.newscientistspace.com/article.ns?id=dn7716
 
No signs of any lakes etc but so far only the southern hemisphere has been observed fully.

Saturn moon Titan 'dry as a bone'


Hopes of finding hydrocarbon oceans on Saturn's smoggy moon, Titan, appear to be dashed, scientists report in Nature.
The moon's atmosphere is thick with methane and ethane, prompting speculation that lakes or oceans of these chemicals may sit on the surface.

The Huygens that landed on Titan sent back images suggesting possible shorelines and rivers.

But an extensive search for tell-tale infrared reflections has now revealed no sign of lakes or seas on Titan.

Scientists who made the measurements using the Keck II telescope in Hawaii suggest the flat surfaces previously spotted on Titan are more likely to be solid and dry.

"We infer mechanisms that produce very flat solid surfaces, involving a substance that was liquid in the past but is not in liquid form at the locations we studied," Robert West of the Jet Propulsion Laboratory in Pasadena, US, and his colleagues wrote.

Northern hemisphere

However, the latest observations were focused entirely on Titan's southern hemisphere. It is just possible the northern region may still contain pools of liquid organic material.

"I would not say that the surface is devoid of liquid methane," lead researcher Dr West said.

Scientists believe Titan's smoggy atmosphere may be similar to that of the primordial Earth and studying it could provide clues to how life began.

Early radar studies showed that Titan was covered with pools of methane - a flammable gas on Earth but liquid on Titan because of the intense atmospheric pressure and cold.

The Cassini space craft, which arrived at Saturn last year on a mission to study the ringed planet and its many moons, also observed intriguing liquid-like features. Since it neared the moon in 2004, it has detected dark, river-like channels.

But Cassini's visible and infrared cameras have failed to find the reflections expected from the surface.

There could be several reasons why the mysterious moon has thrown up such conflicting messages.

"At one time, maybe a liquid water and ammonia mix flowed onto the surface and froze," Dr West told the New Scientist. "That could be smooth on the scale of radar but rough on the scale we see."

Alternatively, Titan's rivers and lakes of hydrocarbon may have evaporated, leaving flat plains of organic material.

A third possibility is that organic particles in Titan's atmosphere settled onto the surface and were blown into low-lying areas, leaving smooth lake-like surfaces.

http://news.bbc.co.uk/1/hi/sci/tech/4745009.stm
 
8/45...

Cassini swoops down on Titan


The Cassini spacecraft swooped just 1075 kilometres above Saturn's cloudy moon Titan on Wednesday, making its second closest approach of the moon to date. The flyby - the eighth of 45 planned – aims to shed some light on whether liquid methane exists on the surface.

The space probe was initially supposed to come within 950 kilometres of Titan, but concerns over whether Titan's dynamic atmosphere would overpower the spacecraft's thrusters and leave it momentarily disoriented led mission managers to pilot a more conservative approach.

A higher altitude means that the onboard cameras will lose a little resolution, says Trina Ray, a science planner for the Cassini mission at NASA's Jet Propulsion Laboratory in Pasadena, California, US.

One of the targets of this pass was potential lakes of methane hiding beneath the thick hydrocarbon clouds. The supposed existence of lakes on the moon has been questioned in the past year.

Dark rivers
Recent infrared images from Earth did not spot large bodies of liquid methane. And, so far, Cassini has not seen reflective surfaces on Titan that would indicate a body of liquid although it and the Huygens probe have spotted dark river-like channels.

But in 2004, Cassini's cameras saw what might be a lake in the southern hemisphere. The peanut-shaped area had smooth edges. "It could be just a broad depression filled in with dark stuff," Ray says. "We just don't know yet. It'll take more observation."

On Wednesday, Cassini flew over southern latitudes on other side of the planet, giving researchers hope that it might have spotted more lake-like features. Its radar bounced microwaves off Titan's surface and will provide high resolution images showing whether the terrain is smooth or rough. Scientists should receive the last of the images and data beamed back from Cassini on Friday.

Star setting
The south pole is covered in thick clouds, perhaps indicating the presence of a heat source in the region. "We know there's some interesting stuff going on down there," Ray told New Scientist.

Cassini also used the star Alpha Pegasus for a neat bit of science by watching it set behind the Titan. First the craft analysed the spectra of the star itself, and then the spectra seen through the haze of the atmosphere - which should help determine the atmosphere's composition.

The craft will next make a pass of Titan on 27 October 2005 at a distance of 1353 kilometres.

http://www.newscientistspace.com/articl ... titan.html
 
Study Suggests Titan May Hold Keys For Exotic Brand Of Life

Study Suggests Titan May Hold Keys For Exotic Brand Of Life

Titan, a Geologically Dynamic World Pasadena CA (JPL) Sep 09, 2005 Synthetic aperture radar images (shown above- see larger image) obtained in February 2005 show that Titan's surface is modified by fluid flows and wind-driven deposits. Previous synthetic aperture radar images have shown features that may be cryovolcanic in origin, such as long flows and linear features that may have formed by tectonic processes.
The latest data argue that Titan has a young and dynamic surface that is modified by all four major geologic processes: volcanism, tectonism, erosion, and impact cratering. All surfaces of solid bodies are shaped by these four processes, and Cassini-Huygens is revealing how each has contributed to the Titan we see today.

The data show a variety of surface drainage patterns that include twisting channels 1 to 2 kilometers-wide (0.6 to 1.2 miles) and up to 200-kilometers-long (124 miles). There is a well-developed drainage pattern associated with a large (450-kilometer, or 280 mile-diameter) basin that has eroded part of the basin's rim on the lower right of the image. These patters are in much larger scales than those imaged by the Huygens probe.

The most surprising new features revealed in the synthetic aperture images are dark lineated streaks, dubbed "cat scratches", which are seen in patches throughout the whole radar swath image.

The "scratches" are interpreted as linear/longitudinal dunes formed by wind transport. Radar images of terrestrial dunes, such as snow dunes in Antarctica, show remarkably similar patterns. Individual "scratches" are 500 meters to 1 kilometer (1,640 feet to 0.6 miles) across and spaced by 1 to 2 kilometer intervals (0.6 to 1.2-mile), straight or undulated, and oriented roughly east-west, suggesting a direction of prevalent winds.


Boulder CO (SPX) Sep 09, 2005
Saturn's moon Titan has long been a place of interest to astrobiologists, primarily because of its apparent similarities to the early Earth at the time life first started. A thick atmosphere composed primarily of nitrogen and abundant organic molecules (the ingredients of life as we know it) are among the important similarities between these two otherwise dissimilar planetary bodies.
Scientists have considered it very unlikely that Titan hosts life today, primarily because it is so cold (-289 degrees Fahrenheit, or -178 Celsius) that the chemical reactions necessary for life would proceed too slowly. Yet previously published data, along with new discoveries about extreme organisms on Earth, raise the prospect that some habitable locales may indeed exist on Titan.

In a paper being presented at the Division for Planetary Sciences 2005 Meeting this week, a team of researchers from Southwest Research Institute (SwRI) and Washington State University say that several key requirements for life now appear to be present on Titan, including liquid reservoirs, organic molecules and ample energy sources.

Methane clouds and surface characteristics strongly imply the presence of an active global methane cycle analogous to Earth's hydrological cycle. It is unknown whether life can exist in liquid methane, although some such chemical schemes have been postulated. Further, abundant hints of ice volcanism suggest that reservoirs of liquid water mixed with ammonia may exist close to the surface.

"One promising location for habitability may be hot springs in contact with hydrocarbon reservoirs," says lead author David H. Grinspoon, a staff scientist in the SwRI Space Science and Engineering Division. "There is no shortage of energy sources [food] because energy-rich hydrocarbons are constantly being manufactured in the upper atmosphere, by the action of sunlight on methane, and falling to the surface."

In particular, the team suggests that acetylene, which is abundant, could be used by organisms, in reaction with hydrogen gas, to release vast amounts of energy that could be used to power metabolism. Such a biosphere would be, at least indirectly, solar-powered.

"The energy released could even be used by organisms to heat their surroundings, helping them to create their own liquid croenvironments," says Grinspoon. "In environments that are energy-rich but liquid-poor, like the near-surface of Titan, natural selection may favor organisms that use their metabolic heat to melt their own watering holes."

The team says these ideas are quite speculative but useful in that they force researchers to question the definition and universal needs of life, and to consider the possibility that life might evolve in very different environments.


http://www.spacedaily.com/news/cassini-05zzzg.html
 
Titan moon occupies 'sweet spot'

Earth and Saturn's moon Titan show striking similarities because both occupy "sweet spots" in our Solar System, researchers have said.

Many processes that occur on Earth also take place on this moon, say scientists participating in the US-European Cassini-Huygens mission.

Wind, rain and volcanism and tectonic activity all seem to play a role in shaping Titan's surface.

One scientist even sees a way that life could survive on the freezing world.

"Titan is perhaps the most Earth-like place in the Solar System other than Earth, in terms of the balance of processes," says Jonathan Lunine, of the University of Arizona, who is an interdisciplinary scientist for Cassini-Huygens.

"Wind-driven processes, river channels, evidence of rain, possible lakes and geological features that may have to do with volcanism and tectonism."

Different chemistry

But the chemistry that drives these processes is radically different between the two worlds. For example, methane seems to perform many of the same roles on Titan that water plays on Earth.

Dr Lunine believes that Earth and Titan both have similar processes occurring because they occupy "sweet spots" in the Solar System. Being in one these spots requires striking a balance between size, or mass, and distance from the Sun.

To demonstrate the idea, Dr Lunine considered three planets in the inner Solar System: Venus, Earth and Mars.

The mass of a body corresponds to an ability to sustain heat flow from its interior, while distance from the Sun is correlated with the ability to retain liquid water, a driver of geological activity on Earth.

Venus is about the same size as Earth. But it is so close to the Sun that any water it had must have boiled off. As such, there is no hydrological cycle and no tectonic activity, says Lunine.

Mars is distant enough from the Sun to retain water. But its small size caused it to cool quickly, turning water to ice and ending large-scale geological activity. Earth occupies an intermediate position - the "sweet spot".

The researcher then turned to three bodies in the outer Solar System: Ganymede, Titan and Triton. The chemistry is different, but similar principles apply.

Jupiter's moon Ganymede, the closest of the three to the Sun, is similar in size to Titan, but lacks the methane and nitrogen that drive liquid processes on the saturnian moon: "It's a kind of baked out version of Titan," said Lunine.

Neptune's moon Triton, much further from the Sun than both Ganymede and Titan, possesses methane and nitrogen. But its small size caused them to freeze, ending any prospect of geological activity.

Scientists have been revealing new details about Titan at the meeting in Cambridge. Ralph Lorenz of the University of Arizona, said that the river channels and flows on Titan are fashioned by "monsoon" events.

'Catastrophic rains'

It takes a relatively long time for methane to build up to a point where it can rain down on Titan's surface. Scientists, therefore, think rains are only occasional, but catastrophic, when they occur.

Evidence also suggests Titan is constantly being resurfaced by a fluid mixture of water and ammonia spewed out by volcanoes and hot springs, explaining why Titan is not littered with impact craters like its neighbours

A surface feature called Ganesa Macula may show just such a flow emanating from a volcanic crater.

The moon's icy surface is also covered with a film, or patina, of organic compounds, Cassini-Huygens data show.

One researcher has even proposed a way for life to survive on the giant Saturnian satellite. It is too cold for organisms to survive on the surface of Titan, where temperatures are about -178C (-289F).

But David Grinspoon of the Southwest Research Institute says organisms could occupy specific niches, such as hot springs. They could use acetylene, in reaction with hydrogen gas, to release enough energy to power metabolism, and possibly to heat their environments.

The Cassini spacecraft entered orbit around Saturn on 1 July 2004 on a mission to explore the ringed planet and its satellites. In December, it released the piggybacked Huygens probe on a collision course with Titan. Two weeks later, Huygens tumbled through the moon's atmosphere and made a successful touchdown on the surface.

New results from the mission were presented at the American Astronomical Society Division of Planetary Sciences meeting in Cambridge.

http://news.bbc.co.uk/1/hi/sci/tech/4229110.stm
 
Cassini Probe Spies Spokes in Saturn's Rings

The Cassini spacecraft orbiting Saturn has finally spotted spokes cutting across the planet's rings, a phenomenon astronomers have long hoped their plucky orbiter might find.

While flying past the dark side of Saturn's B ring, Cassini's camera eye photographed the spokes - which appear as radial markings - in a series of three images taken over about 27 minutes. The find is a gem of sorts for mission imaging scientists, who have been hunting for the ring spokes since Cassini arrived at Saturn.


"We've been on the lookout for them since February, 2004," said Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, CO, of the spokes in an e-mail interview. "Spokes are one of those Saturn-system phenomena that we are keenly interested in understanding."

Saturn's odd ring spokes were first discovered during NASA's Voyager mission, which swung passed the planet in the 1980s, and later observed by astronomers using the Hubble Space Telescope.





NASA's Voyager spacecraft photographed spokes in Saturn's rings in the 1980s.


IMAGE: NASA/VOYAGER


But spokes were noticeably absent when Cassini made its final approach toward Saturn in February 2004, and are a prime target for astronomers because their role and formation within the planet's rings are not fully understood.





"These are among the things we hope to learn," said Porco, who participated in the Voyager mission as well. "[The spokes] are obviously related to a host of processes...and may point to some important effects in understanding the magnetic field and the planet's magnetosphere, and how these systems interact with the rings and atmosphere."





Porco and her imaging team did not initially expect to observe ring spokes until about 2007, when certain models predicted spoke formation and visibility.





"Well, in some sense we should have expected, if the recent models are correct, to see them on the dark side where the photoelectron abundance is low," Porco said of the spokes. "So, I was surprised to see them. But once they showed up, I realized we should have expected them there all along."




While the images were released on Sept. 13, Cassini actually photographed the ring spokes on Sept. 5, 2005, using clear filters and its wide-angle camera from a distance of about 198,000 miles (318,000 kilometers) from Saturn. The spokes themselves are fairly faint, and are about 60 miles (100 kilometers) wide and 2,200 miles (3,500 kilometers) long, researchers said.



Unlike Voyager or Hubble, Cassini is in a unique position to study ring spoke phenomena at Saturn, Porco said.



"Remember, Voyager was just a flyby, Cassini is in orbit," Porco said, adding that Cassini is a vastly superior observation platform when compared to Voyager. "We have the opportunity for monitoring them and their behavior, their comings and goings, how they evolve, when they appear and disappear."



By observing the spokes on the dark side of Saturn's rings, Cassini recreated a bit of space exploration history. Its predecessor, Voyager, also first observed the ring spoke phenomena while photographing the unilluminated side of the Saturn's rings.



"It felt like the old days, when we first saw the spokes," Porco said. "They are one weird phenomena and it was a joy to see them again...especially since we hadn't seen them yet and were eager to know why."

http://news.yahoo.com/s/space/20050915/ ... turnsrings
 
Spokes!Source
Cassini sees dusty ‘spokes’ in Saturn’s rings
18:06 19 September 2005
NewScientist.com news service
Maggie McKee

Faint spokes of fine dust stretch outward across Saturn's outer B ring in two images from Cassini (Image: NASA/JPL/Space Science Institute)

The Cassini spacecraft has finally spotted dusty "spokes" in Saturn's rings that were first seen about 25 years ago. Researchers hope to monitor how the spokes wax and wane over time to see if the dusty streams signal a change in Saturn's rotation rate.

Wedge-shaped trails of dust stretching up to 20,000 kilometres in length were first seen radiating outward in Saturn's outer B ring during flybys of NASA's twin Voyager spacecraft in 1980 and 1981. Since then, the Hubble Space Telescope has also imaged the spokes, which are thought to be caused by dust particles that become charged and float above the plane of the main ring.

The dust may come from objects crashing into the rings, or when changes in the magnetic field around Saturn allow charged particles to fly radially outwards, producing currents that levitate some dust in their path. "There's no commonly agreed on theory for their formation," says Cassini team member Carl Murray, an astronomer at Queen Mary, University of London, UK.

But Cassini had not detected the spokes since it arrived at Saturn in July 2004. "Some people thought the reason we hadn't seen them was because you needed the right viewing geometry," Murray told New Scientist.

Spoke too soon?
The relative orientation of Saturn, its rings and the Sun means that, twice during the planet's 30-year orbit, its rings lie just about edge-on to the Sun. Astronomers think that makes the spokes easier to view and indeed the Voyager craft observed the spokes during one of these periods. So the Cassini team expected the rings to become visible again in 2007, as the rings approach the same alignment.

Now, Cassini's imaging instruments have seen faint spokes in a series of images taken over 30 minutes on 5 September. The spokes are about 3500 km long, 100 km wide and were seen when Saturn's rings were tilted by about 20° in relation to the plane of the Sun's orbit.

"Having resigned ourselves to waiting, to see them was a surprise," Murray told New Scientist. Seeing the spokes now suggests they should have been visible to Cassini over the last year but have simply not been present.

“Enormous consequences”
Studying the pattern of when the spokes appear may reveal more fundamental changes within Saturn. Cassini imaging team member Carolyn Porco of the Space Science Institute in Boulder, Colorado, US, had analysed the spokes seen by Voyager and found they correlated with bursts of radio waves associated with Saturn's magnetic field.

Cassini has already discovered that the incidence of these radio wave bursts has changed since the Voyager days, suggesting Saturn's rotation rate may also have changed. "That would be a finding of enormous consequence, so we'll be looking very closely to see if the frequency of spoke activity has changed too," says Porco.

"Work we have done with the latest data from Cassini reveals that the rotation rate as predicted by the magnetic field is different to that observed by the Pioneer and Voyager spacecraft," says Michele Dougherty, lead researcher for Cassini's magnetometer instrument at Imperial College in London, UK. "But we are presently unsure about what may be driving it."
:)
 
Cassini spots huge “spear” on Saturn moon

Cassini spots huge “spear” on Saturn moon
13:01 27 September 2005
NewScientist.com news service
Stephen Battersby

http://www.newscientistspace.com/article.ns?id=dn8057

Tethys is one of Saturn's inner moons, orbiting about 300,000 kilometres from the planet - closer than our Moon is to Earth. Scientists already knew that the 500-kilometre moon bears one huge crater, Odysseus, and a unique giant canyon system called Ithaca Chasma.

They are now hoping to find out how Ithaca Chasma formed - whether, perhaps, it is related to the impact that created Odysseus. They also hope to discover what processes have resurfaced some areas of Tethys, smoothing out the old, heavily cratered terrain.

Cassini's highly detailed pictures should help. Although the spacecraft was not originally supposed to come closer than 30,000 kilometres, the navigation team worked out a way to skim within 1500 kilometres of Tethys without upsetting the rest of Cassini's complex schedule. From this close, some of the images reveal details smaller than 20 metres across.

Mission scientists have only just begun looking at the new data, but they should release their initial conclusions in the coming days. They will want to get as much as possible out of this visit, because Cassini may never return to Tethys.

Related Articles
Titan may boast extraterrestrial sea
http://www.newscientist.com/article.ns? ... 725183.700
24 September 2005
Cassini sees dusty ‘spokes’ in Saturn’s rings
http://www.newscientist.com/article.ns?id=dn8021
19 September 2005
Cassini captures Tethys in all her glory
http://www.newscientist.com/article.ns?id=dn6723
24 November 2004
Weblinks
Cassini-Huygens mission to Saturn and Titan
http://saturn.jpl.nasa.gov/home/index.cfm
The Planetary Society: Tethys
http://www.planetary.org/saturn/tethys.html
 
Cassini flyby of Hyperion reveals tortured world

Just two days after Cassini visited Saturn's moon Tethys, it has flown past Hyperion, one of the smaller and odder moons of the ringed planet.

Hyperion is potato-shaped: 360 kilometres long, but only about 250 kilometres across. Its rotation is chaotic, tumbling unpredictably under the influence of Saturn's and Titan's gravity. And it is exceptionally dark for a Saturnian moon, reflecting only 30% of the light that falls on it, with a distinctly red tint.

The biggest question for Cassini to answer is why Hyperion is so misshapen when other asteroids and moons of about this size are much more spherical. One theory is that it is merely a fragment of a larger moon that was shattered in a violent impact.

Cassini's pictures certainly show a tortured world, riven by craters and girdled by a giant cliff face tens of kilometres high.

The new images were gathered early on Monday morning, from as close as 500 kilometres to Hyperion's surface. During the flyby, Cassini's radar also measured slight changes in the speed of the spacecraft. This will give an idea of the strength of Hyperion's gravity, and therefore its mass. Mission scientists hope to discover whether the moon is solid rock or a loosely packed "rubble pile".

The Cassini team should also be able to map the chemical make-up of Hyperion's surface to discover whether it is dusted with dark material drifting in from Saturn’s sooty outer moon, Phoebe.

http://www.newscientist.com/article.ns?id=dn8065
 
Titan's bright spot revealed by Cassini


The Cassini spacecraft has spotted the brightest area yet on Saturn's moon, Titan - but how it formed remains a mystery.

"It's the brightest area on Titan in every wavelength we've looked at," says Jason Barnes, at the Lunar and Planetary Laboratory at the University of Arizona, US.

The bright red spot is about 400 kilometres across and lies south-east of another bright area named Xanadu. But it is almost twice as bright as Xanadu. "The question is why," says Barnes.

The reflective area could indicate a layer of methane-rich ground fog or the sheen of methane rainfall. Other observations indicate that Titan may have seas of liquid hydrocarbons and methane clouds.

The Visual and Infrared Mapping Spectrometer aboard Cassini has observed the spot over a period of nine months, and the Keck Observatory in Hawaii has observations going back over 4 years.

The persistence of the spot suggests it may not involve clouds, as these tend to break up within hours or days on Titan. However, a long-lived cloud controlled by the flow of the atmosphere across surface features, such as small mountains, might be possible. On the other hand, the spectrum of the spot does not correlate well with that of clouds.

Hovering fog
It may be a fog hovering over a lake, hot springs or volcanic region. "But if it's ground fog, it's really persistent," Barnes told New Scientist.

A bright arc in Titan's surface, known as "The Smile", might also be responsible for the new bright spot. "The Smile" could vent some material that blows northeast and then settles on the bright region. The spot's colour and brightness suggest that it is a relatively recent formation.

The team's early speculation was that the area could be a volcanic hot spot. But Cassini's instruments did not find elevated surface temperatures.

Another possible explanation is that the spot is made of highly reflective frozen carbon dioxide. However, Cassini does not have the capability to confirm this.

NASA's Monika Kress and Chris McKay predicted in 2004 that there should be a lot of carbon dioxide on Titan, given a predicted bombardment by carbon-dioxide-rich comets early in the moon's existence.

http://www.newscientistspace.com/articl ... ssini.html
 
A little more info on the same story...

A 300-mile-wide patch that outshines everything else on Titan at long infrared wavelengths appears not to be a mountain, a cloud or a geologically active hot spot, University of Arizona scientists and Cassini team members say.
"We must be looking at a difference in surface composition," said Jason W. Barnes, a postdoctoral researcher at UA's Lunar and Planetary Lab. "That's exciting because this is the first evidence that says not all of the bright areas on Titan are the same. Now we have to figure out what those differences are, what might have caused them."

When NASA's Cassini spacecraft flew by Titan on March 31 and again on April 16, its visual and infrared mapping spectrometer saw a feature that was spectacularly bright at 5-micron wavelengths just southeast of the continent-sized region called Xanadu.

The bright spot occurs where Cassini's visible-wavelength imaging cameras photographed a bright arc-shaped feature approximately the same size in December 2004 and February 2005.

Cassini's radar instrument, operating in the "passive" mode that is sensitive to microwaves emitted from a planetary surface, saw no temperature difference between the bright spot and surrounding region. That rules out the possibility that the 5-micron bright spot is a hot spot, such as a geologically active ice volcano, Barnes said.

Cassini microwave radiometry also failed to detect a temperature drop that would show up if some two-mile high mountain rose from Titan's surface, he said.

And if the 5-micron bright spot is a cloud, it's a cloud that hasn't moved or changed shape for three years, according to ground-based observations made at the Keck Telescope and with Cassini's visual and infrared mapping spectrometer during five different flybys. "If this is a cloud," Barnes said, "it would have to be a persistent ground fog, like San Francisco on steroids, always foggy, all the time."

"The bright spot must be a patch of surface with a composition different from anything we've seen yet. Titan's surface is primarily composed of ice. It could be that something is contaminating the ice here, but what this might be is not clear," Barnes said.

"There's a lot left to explore about Titan. It's a very complex, exciting place. It's not obvious how it works. It's going to be a lot of fun over the next couple of years figuring out how Titan works," he said.

http://www.spacedaily.com/news/saturn-titan-05zc.html
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A little more info on the same story...

A 300-mile-wide patch that outshines everything else on Titan at long infrared wavelengths appears not to be a mountain, a cloud or a geologically active hot spot, University of Arizona scientists and Cassini team members say.
"We must be looking at a difference in surface composition," said Jason W. Barnes, a postdoctoral researcher at UA's Lunar and Planetary Lab. "That's exciting because this is the first evidence that says not all of the bright areas on Titan are the same. Now we have to figure out what those differences are, what might have caused them."

When NASA's Cassini spacecraft flew by Titan on March 31 and again on April 16, its visual and infrared mapping spectrometer saw a feature that was spectacularly bright at 5-micron wavelengths just southeast of the continent-sized region called Xanadu.

The bright spot occurs where Cassini's visible-wavelength imaging cameras photographed a bright arc-shaped feature approximately the same size in December 2004 and February 2005.

Cassini's radar instrument, operating in the "passive" mode that is sensitive to microwaves emitted from a planetary surface, saw no temperature difference between the bright spot and surrounding region. That rules out the possibility that the 5-micron bright spot is a hot spot, such as a geologically active ice volcano, Barnes said.

Cassini microwave radiometry also failed to detect a temperature drop that would show up if some two-mile high mountain rose from Titan's surface, he said.

And if the 5-micron bright spot is a cloud, it's a cloud that hasn't moved or changed shape for three years, according to ground-based observations made at the Keck Telescope and with Cassini's visual and infrared mapping spectrometer during five different flybys. "If this is a cloud," Barnes said, "it would have to be a persistent ground fog, like San Francisco on steroids, always foggy, all the time."

"The bright spot must be a patch of surface with a composition different from anything we've seen yet. Titan's surface is primarily composed of ice. It could be that something is contaminating the ice here, but what this might be is not clear," Barnes said.

"There's a lot left to explore about Titan. It's a very complex, exciting place. It's not obvious how it works. It's going to be a lot of fun over the next couple of years figuring out how Titan works," he said.

http://www.spacedaily.com/news/saturn-titan-05zc.html
 
Titan's Enigmatic Infrared-Bright Spot Is Surface Make-Up


A 300-mile-wide patch that outshines everything else on Titan at long infrared wavelengths appears not to be a mountain, a cloud or a geologically active hot spot, University of Arizona scientists and Cassini team members say.

We must be looking at a difference in surface composition," said Jason W. Barnes, a postdoctoral researcher at UA's Lunar and Planetary Lab. "That's exciting because this is the first evidence that says not all of the bright areas on Titan are the same. Now we have to figure out what those differences are, what might have caused them."

When NASA's Cassini spacecraft flew by Titan on March 31 and again on April 16, its visual and infrared mapping spectrometer saw a feature that was spectacularly bright at 5-micron wavelengths just southeast of the continent-sized region called Xanadu.

The bright spot occurs where Cassini's visible-wavelength imaging cameras photographed a bright arc-shaped feature approximately the same size in December 2004 and February 2005.

Cassini's radar instrument, operating in the "passive" mode that is sensitive to microwaves emitted from a planetary surface, saw no temperature difference between the bright spot and surrounding region. That rules out the possibility that the 5-micron bright spot is a hot spot, such as a geologically active ice volcano, Barnes said.

Cassini microwave radiometry also failed to detect a temperature drop that would show up if some two-mile high mountain rose from Titan's surface, he said.

And if the 5-micron bright spot is a cloud, it's a cloud that hasn't moved or changed shape for three years, according to ground-based observations made at the Keck Telescope and with Cassini's visual and infrared mapping spectrometer during five different flybys. "If this is a cloud," Barnes said, "it would have to be a persistent ground fog, like San Francisco on steroids, always foggy, all the time."

"The bright spot must be a patch of surface with a composition different from anything we've seen yet. Titan's surface is primarily composed of ice. It could be that something is contaminating the ice here, but what this might be is not clear," Barnes said.

"There's a lot left to explore about Titan. It's a very complex, exciting place. It's not obvious how it works. It's going to be a lot of fun over the next couple of years figuring out how Titan works," he said.

Barnes and 34 other scientists report the research in the Oct. 7 issue of Science. Authors include UA Lunar and Planetary Laboratory scientists and Cassini team members Robert H. Brown, head of Cassini's visual and infrared mapping spectrometer team; Elizabeth P. Turtle and Alfred S. McEwen of the Cassini imaging team; Ralph D. Lorenz of the Cassini radar team; Caitlin Griffith of the Cassini visual and infrared mapping team; and Jason Perry and Stephanie Fussner, who work with McEwen and Turtle on Cassini imaging.

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, Calif., manages the mission for NASA's Science Mission Directorate, Washington, D.C. 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, Colo. The Visual and Infrared Mapping Spectrometer team is based at The University of Arizona in Tucson .

http://www.sciencedaily.com/releases/20 ... 074044.htm
 
Surface Geology Creates Clouds On Titan

Cracks Or Cryovolcanoes? Surface Geology Creates Clouds On Titan

Adds Brown: "For a long time we've wondered why there is methane in the atmosphere of Titan at all, and the answer is that it spews out of the surface. And what is tremendously exciting is that we can see it, from Earth; we see these big clouds coming from above these methane vents, or methane volcanoes. Everyone had thought that must have been the answer, but until now, no one had found the spewing gun."
Pasadena CA (SPX) Oct 20, 2005
Like the little engine that could, geologic activity on the surface of Saturn's moon Titan-maybe outgassing cracks and perhaps icy cryovolcanoes-is belching puffs of methane gas into the atmosphere of the moon, creating clouds.
This is the conclusion of planetary astronomer Henry G. Roe, a postdoctoral researcher, and Michael E. Brown, professor of planetary astronomy at the California Institute of Technology. Roe, Brown, and their colleagues at Caltech and the Gemini Observatory in Hawaii based their analysis on new images of distinctive clouds that sporadically appear in the middle latitudes of the moon's southern hemisphere. The research will appear in the October 21 issue of the journal Science.

The clouds provide the first explanation for a long-standing Titan mystery: From where does the atmosphere's copious methane gas keep coming? That methane is continuously destroyed by the sun's ultraviolet rays, in a process called photolysis. This photolysis forms the thick blanket of haze enveloping the moon, and should have removed all of Titan's atmospheric methane billions of years ago.

Clearly, something is replenishing the gas-and that something, say Roe and his colleagues, is geologic activity on the surface. "This is the first strong evidence for currently active methane release from the surface," Roe says.

Adds Brown: "For a long time we've wondered why there is methane in the atmosphere of Titan at all, and the answer is that it spews out of the surface. And what is tremendously exciting is that we can see it, from Earth; we see these big clouds coming from above these methane vents, or methane volcanoes. Everyone had thought that must have been the answer, but until now, no one had found the spewing gun."

Roe, Brown, and their colleagues made the discovery using images obtained during the past two years by adaptive optics systems on the 10-meter telescope at the W. M. Keck Observatory on Mauna Kea in Hawaii and the neighboring 8-meter telescope at the Gemini North Observatory. Adaptive optics is a technique that removes the blurring of atmospheric turbulence, creating images as sharp as would be obtained from space-based telescopes.

"These results came about from a collaborative effort between two very large telescopes with adaptive optics capability, Gemini and Keck," says astronomer Chadwick A. Trujillo of the Gemini Observatory, a co-author of the paper.

"At both telescopes, the science data were collected from only about a half an hour of images taken over many nights. Only this unusual 'quick look' scheduling could have produced these unique results. At most telescopes, the whole night is given to a single observer, which could not have produced this science."

The two telescopes observed Titan on 82 nights. On 15 nights, the images revealed distinctive bright clouds-two dozen in all-at midlatitudes in the southern hemisphere. The clouds usually popped up quickly, and generally had disappeared by the next day. "We have several observations where on one night, we don't see a cloud, the next night we do, and the following night it is gone," Roe says.

Some of the clouds stretched as much as 2,000 km across the 5,550 km diameter moon. "An equivalent cloud on Earth would cover from the east coast to the west coast of the United States," Roe says.

Although the precise altitude of the clouds is not known, they fall somewhere between 10 km and 35 km above the surface, within Titan's troposphere (most cloud activity on the earth is also within its troposphere).

Notably, all of the clouds were located within a relatively narrow band at around 40 degrees south latitude, and most were clustered tightly near 350 degrees west longitude. Both their sporadic appearance and their specific geographic location led the researchers to conclude that the clouds were not arising from the regular convective overturn of the atmosphere due to its heating by the sun (which produces the cloud cover across the moon's southern pole) but, rather, that some process on the surface was creating the clouds.

"If these clouds were due only to the global wind pattern, what we call general circulation, there's no reason the clouds should be linked to a single longitude. They'd be found in a band around the entire moon," Roe says.

Another possible explanation for the clouds' patchy formation is variation in the albedo, or brightness, of the surface. Darker surfaces absorb more sunlight than lighter ones. The air above those warmer spots would be heated, then rise and form convective clouds, much like thunderstorms on a summer's day on Earth.

Roe and his colleagues, however, found no differences in the brightness of the surface at 40 degrees south latitude. Clouds can also form over mountains when prevailing winds force air upward, but in that case the clouds should always appear in the identical locations. "We see the clouds regularly appear in the same geographic region, but not always in the exact same location," says Roe.

The other way to make a cloud on Titan is to raise the humidity by directly injecting methane into the atmosphere, and that, the scientists say, is the most likely explanation here.

Exactly how the methane is being injected is still unknown. It may seep out of transient cracks on the surface, or bubble out during the eruption of icy cryovolcanoes.

Although no such features have yet been observed on the moon, Roe and his colleagues believe they may be common. "We think there are numerous sources all over the surface, of varying size, but most below the size that we could see with our instruments," he says.

One large feature near 350 degrees west longitude is probably creating the clump of clouds that forms in that region, while also humidifying the band at 40 degrees latitude, Roe says, "so you end up creating areas where the humidity is elevated by injected methane, making it easier for another, smaller source to also generate clouds.

They are like weather fronts that move through. So we are seeing weather, on another planet, with something other than water. With methane. That's cool. It's better than science fiction."


http://www.spacedaily.com/news/saturn-titan-05zd.html
 
Titan Weather: Cloudy Every 15 Years

Titan Weather: Cloudy Every 15 Years



About two years ago, before the Huygens probe arrived at Titan, Henry Roe, a graduate student I was working with at Berkeley, discovered clouds on Titan. He was the first person to get images of what he thought were clouds on the south pole.

We sent his results off for publication, which is what a good graduate student is supposed to do, and the editor sent it out for review. But the reviewer said, "Nope, those aren't clouds. That's a mistake in the data processing. It's just an artifact." So I had the student assemble the raw data as well as the processed data, and the clouds were still there in the raw data.

So we were predicting clouds on the southern rim of Titan. When Henry first saw them, they had just appeared there. They hadn't been there before. So the Cassini orbiter flew under Titan and took pictures of the south pole looking up - and there were the clouds. It's really spectacular. It was a real vindication for Henry Roe. And it shows the advantage of actually being there to see them, of being able to get underneath Titan and look up at them, rather than looking at them edge-on.

In the images that were taken over a five-hour period in July, you can see that the clouds have changed. If you fly in and out of Dallas in the summer, you'll often see thunderstorm lines up along the plains. They change, too, over a period of about an hour or so.

So the clouds on Titan changed on about the same time scale as a thunderstorm system on Earth. You look at them and they could be clouds on Earth. They're white, fluffy, billowing. But they're not water. There's no water anywhere near here. These are methane, liquid methane clouds. And the temperature there is about minus 200 Centigrade. And there are clouds and they're moving.

On Earth, clouds tend to form mostly in the tropics, where the sun is the brightest and the thermal contrast between the dark cycle and the light cycle, night and day, is the strongest. That causes upwelling, which drives clouds to form near the equator.

On Titan, we don't see clouds at the equator. We see clouds at the pole. Titan is different from Earth in that the place on Titan which has the strongest contrast between dark and light is the poles. At Titan's equator, the sun goes up and sets, but the atmosphere is so thick that at nighttime the temperature is the same as the daytime.

The thermal response of the atmosphere is much, much longer than the Titan day, which is 16 Earth days. But it's shorter than the Titan year, which is 30 Earth years.

In fact, in the equatorial mid-latitude regions of Titan, the temperature hasn't changed in 20 years. It's exactly the same to half a degree. So it's very easy to predict. If you were a weatherman working on Titan, in the mid-latitude, your report would be, "Temperature today and tomorrow will be exactly like it was yesterday. And we can predict that for the next 20 years it will be exactly the same."

The only place on Titan where you can have a light-dark contrast, which is what drives this kind of storm activity, is in the polar regions, not at the equator. In that sense, it's different from the Earth in its meteorology.

These clouds are now gone. We don't see them any more. They were only there during the height of Titan's southern summer, when the southern pole was getting 24 hours of sunlight. That's when the clouds came. Now that fall has come to Titan, the clouds have gone away. They were apparently only there for a couple of years. And our prediction is that in another 15 years, clouds will form at the north pole, as that becomes sunlit summer. So, I'm going too try to stick around to see that.

My buddy Henry Roe, who's now a post-doc, also detected clouds in Titan's mid-latitudes. He's seeing these thin clouds, sort of like Cirrus clouds, at 40 degrees south, all the time. There are two possible explanations. One is that, like on Earth, there's a certain convergence there, and that's creating clouds. It's an atmospheric effect. If that's true, as we watch it, with seasons the clouds will move north and in 10 years they'll be up at 30 degrees north.

The other possibility is that there is a cryovolcano at 40 degrees south, a source of methane, a volcano ejecting methane. Remember the reason we once thought Titan had an ocean was that something had to be resupplying the atmosphere with methane. Well, there's no ocean. So you might be wondering, How is Titan resupplying the atmosphere then? Good question. It's not coming from an ocean; what could it be coming from? Henry suggested that these clouds could be caused by a cryovolcano. And if you calculate how much methane this volcano would have to put out to make these clouds, it turns out to be just the right amount to keep the atmosphere in methane.

So there are dueling views. Some people think these clouds are caused by atmospheric circulation, some people think it's a cryovolcano. We don't know. We'll just have to wait and see.

http://www.physorg.com/news7745.html
 
Titan's Rocks Of Ice

Titan's Rocks Of Ice

"I think we landed in a stream bed. The rocks you can see in the picture are solid water."
Interview with Christopher McKay
for Astrobiology Magzine
Moffett Field CA (SPX) Nov 08, 2005
Huygens sent back only one picture from the surface of Titan. Some people ask, "Are there any more pictures?" They're used to the Mars rovers, where every day you get a new picture because they're moving.
Huygens doesn't have any wheels or any motion, so it lands and whatever orientation the camera's pointing in, that's the scene, the only scene it takes a picture of. So we have an hour and a half of the same picture. But it's a pretty cool picture.

I think we landed in a stream bed. The rocks you can see in the picture are solid water.

Titan is minus 180 Celsius (minus 292 Fahrenheit). At this cold temperature, H2O is a rock. It is not a volatile; it is not a fluid; it is not an ice, in the sense that you might think of ice as an easily malleable solid form of a fluid. It is a rock. It is as hard as granite and acts like granite.

The stream bed was probably made by liquid methane. So we're probably sitting in the dry bed of a liquid methane stream. Now, if these rocks are solid water, they would sink in liquid methane, just like rocks on Earth sink in water. And rocks are hard, so they're going to get tumbled by liquid and they're going to be rounded. The rocks look like stream pebbles.

There are some puzzles with this image, though. One puzzle is, Are the rocks really made out of water? When the probe landed, we said, That's got to be water. What else could it be? But there are some problems with that interpretation. The spectral data is not consistent with water. The GCMS team hasn't published their results and haven't shown the data, but they say that they don't see the spectral signature of water.

But even if you had a small impurities mixed in with the water, they might hide the spectral signature. For example, if you mix in a little bit of organic goo, it looks brown. Imagine a dirty snow bank. It's hard to tell if it's really snow, because snow is supposed to be white. So small-level impurities could hide the water.

The other thing is that the dielectric constant of the ground, as measured by the Huygens impedance probe, is not consistent with water ice. But the antenna of the probe got bent in the landing, so we're not sure of its calibration. We've got to sort that out. So we can't rule out water.

If we look at the density of Titan, it's 1.9 grams per square centimeter, which means it's got to be 50 percent water by mass. This is the outer solar system. Everything is 50 percent water by mass, roughly. Titan is no exception. Only Io is not, because it's been dehydrated. And the water's all going to be on the top.

Billions of years ago, when the Earth formed, it was completely molten. Everything was molten. And it cooled, and the rock solidified. That was the primary source of rocks on Earth, the solidification of the magma Earth. Rocks on Earth are mainly silicates, they're mostly made out of glass, SiO2-type substances. They melt at very high temperatures, a couple of thousand degrees. So once the Earth cooled down below a couple thousand degrees, it became full of rocks.

Think of Titan the same way. Titan formed very hot, completely molten. When it cooled down to a couple thousand degrees, half of it condensed to form rocks. The other half was still water, still steam. It didn't condense until the temperature fell below 0 degrees Celsius (minus 32 degrees Fahrenheit). Then the water all turned to solid and became hard, and as the temperature became colder, that stuff got harder and harder.

So when Titan formed, it should have formed with a rocky inside, and then a huge layer of frozen water on top of it. So this 50 percent water by mass, we expect that mass to be on the top, to be the crust of Titan. That's why we think that Titan has a several-thousand-kilometer-thick layer of ice on the surface. On Titan we don't call it an ocean, we call it the mantle, because it's not liquid, it's solid.

Some people think there could be a liquid underneath, a methane-ammonia-water mixture, but we still expect the surface to be basically frozen water. It's just like Europa. The only difference is that it's got an atmosphere above it. That's why we can't figure out what the rocks can be besides water. Because all the other moons that are like it - Ganymede, Callisto, Europa - when we look at their surfaces, they're water. If you take off Titan's atmosphere, underneath it all, it should be just like the Galilean moons: water-dominated surfaces.

So if it's not water, what could it possibly be? I don't know. This is a real puzzle. And people are lining up on different sides. There are people who say, It's definitely not water. When I ask them, What is it? they go, I don't know, but it's not water. The best number two guess would be carbon dioxide, CO2. But from an abundance point of view it's hard to imagine, that the surface is really littered with CO2 rocks and not water rocks.

http://www.spacedaily.com/news/saturn-titan-05zk.html
 
Cassini provides compelling evidence gravitational wakes in Saturn's rings



By watching a distant star as it passed behind Saturn's outer rings, Cornell University astronomers on NASA's Cassini-Huygens mission to Saturn have found the most direct evidence to date of patterns, called gravitational wakes, within the planet's outer rings.

Image: Astronomy professor Phil Nicholson and research associate Matt Hedman take Saturn for a spin outside the Space Sciences Building. (Jason Koski/Cornell University Photography)

The patterns, thin, parallel striations like spokes on a pinwheel, have been theorized since the 1970s, but their small scale (just 100 meters -- 328 feet -- wide) makes them impossible to see even with the spacecraft's high-resolution camera. The new evidence of their existence, says Phil Nicholson, Cornell professor of astronomy, gives scientists clues about how thick Saturn's rings are and how their constituent bodies interact.

Nicholson presented his findings in September at the American Astronomical Society's 37th Division for Planetary Sciences meeting in Cambridge, England.

Nicholson and postdoctoral researcher Matt Hedman used Cassini's visual and infrared mapping spectrometer (VIMS) to take spectra of the star Omicron Ceti (also known as Mira) in quick succession during four three-hour intervals, or stellar occultations, during which the star passed behind Saturn's A and B rings. (The A ring is the planet's outermost visible ring; the B ring is closer to Saturn.) With the more than 100,000 spectra from each occultation, Nicholson and Hedman plotted the amount of near-infrared light that filtered through the rings. They then compared the optical depth -- the amount of light blocked by the ring material -- at several points throughout the occultation. In the comparison, they noticed an unexpected asymmetry: More light filtered through at points on the star's way out of the occultation than at corresponding points equidistant from the planet on the star's way in.

At first, Nicholson and Hedman considered whether the asymmetry could be explained by the spacecraft's slight shift in vantage point over the occultation. But Nicholson pointed out that the distance between the spacecraft and the star is virtually infinite. Lines drawn between the two at either end of the occultation are for all practical purposes parallel -- so the angle between the ring plane and the line of sight between Cassini and the star doesn't change significantly.

More likely, said Nicholson, is that the small chunks of water ice that comprise the rings are arranged in stripes radiating outward at a skewed angle, like spokes on a pinwheel. The so-called gravitational wakes form when the small objects' gravitational attraction to each other competes with the tendency of tidal forces from Saturn to pull them apart.

"When the wakes are seen almost end on, the A ring appears at its most transparent," said Nicholson, "whereas when the wakes are seen from the side, the ring becomes almost opaque."

Though Cassini, which arrived at the giant planet in June 2004, can't get close enough to see the wakes directly (the spacecraft was about 1.6 million kilometers away from Saturn when the occultations occurred), Nicholson has already heard from other Cassini researchers with independent observations supporting the existence of gravitational wakes.

"I suspect in the end that many Cassini instruments will be seeing the same kind of phenomenon," he said. Still, while he expected some evidence of the wakes, the spacecraft's position during the occultations -- with only 3.5 degrees between the ring plane and the line of sight to the star -- made the effect striking.

"We were certainly surprised," he said. "We were not expecting it to be as obvious. At one level, it's just kind of neat to us who study rings. For those of us in the business it's nice to get direct evidence of the wakes."

On a more practical level, though, the finding gives scientists a new piece of information about the rings' micro-structure and internal dynamics: specifically, how the ice chunks move as they are pulled toward each other and collide, and as Saturn's tidal force shears them apart again.

It also gives researchers a tool for judging the overall thickness of Saturn's rings. Throughout Cassini's four-year mission, astronomers will collect data from dozens of similar experiments. Since each will be made from a different viewing angle, astronomers will then compare how marked the wakes' effect is across the series. That information will allow them to estimate the rings' thickness (their north-south span) -- which is thought to be as little as 10 meters -- 33 feet.




Image: A diagram of Saturn's rings illustrating the paths taken by the star Omicron Ceti during four recent occulatations observed by the Cassini spacecraft. Bars at each path show the amount of light that filtered through the rings at points along the occultation. Inset boxes illustrate the orientation of gravitational wakes relative to the direction from the spacecraft to the star at select points in the A ring.

Using the wakes to estimate the rings' thickness is similar to using sunlight to estimate the widths of slats on a set of vertical blinds. If the blinds are open and the sun is high in the sky, the blinds will let in nearly all the light. But as the sun sets to one side, the blinds -- in the same position -- will begin to block more and more light, because of their width. Similarly, if the rings are very thick, the spacecraft will continue to see the wakes' effect from higher elevations; if they are very thin, evidence of the wakes will begin to diminish when the angle between Cassini's line of sight and the ring plane is still quite small.

"This may be the best way of directly learning the thickness of the rings," Nicholson said.

Cassini's VIMS team is led by Robert Brown at the University of Arizona's Lunar and Planetary Laboratory. During Cassini's Saturn tour, the spacecraft will complete 74 orbits of the planet, 45 flybys of the moon Titan and many flybys of Saturn's other moons.

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 in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL.

Source: Cornell University

http://www.physorg.com/news8083.html
 
Cassini snapshot reveals Saturn?s volcanic moon

NASA's Cassini spacecraft has captured unique views of two of Saturn's moons. The probe?s first close encounter with the large moon Rhea was somewhat eclipsed by a sidelong snapshot of the moon Enceladus, revealing active volcanic plumes above its surface.

On a previous, much closer pass by Enceladus, Cassini detected that the south pole of Enceladus is spewing out a vast plume of water vapour that stretches hundreds of kilometres from the moon's surface and keeps Saturn's E-ring topped up ? but it has now captured the first images of this activity. On Sunday, 27 November, Cassini was positioned so that the Sun was behind the moon, causing one side of Enceladus to be illuminated as a fine crescent, with its volcanic plumes backlit.

Enceladus is only the third body in the solar system to show signs of active volcanism, besides Earth and Io, Jupiter's moon. Even though this volcanism is exceptionally gentle, planetary scientists cannot yet work out what is driving it. The new pictures could help by revealing the muzzle velocity of the moon's plumes.

Evil twin
A day earlier, on 26 November, Cassini flew just 500 kilometres from the surface of Rhea. At 1500 kilometres across, Rhea is Saturn's second largest moon. From a first look at the raw images, there are few surprises ? the landscape is the same wasteland seen during more distant flybys, featuring craters up to 400 km wide. But revelations may still come from a more careful analysis.

"It was good to finally get a decent look at Tirawa, Rhea's largest crater, and its 'evil twin' directly to the northeast," says outer-moon expert William McKinnon of Washington University in St. Louis, US. A minor surprise is that neither of these craters has rings around its centre from the impacts which created them, which is to be expected given their size.

"Tirawa was first spotted in Voyager images, but the twin remained a secret until Cassini," McKinnon adds. "Both basins appear to be similarly old, and I conjecture that they may be the result of a binary impact, like East and West Clearwater in Canada."

http://www.newscientistspace.com/article.ns?id=dn8386
 
Titan's atmosphere revealed as multilayered mystery

Titan's atmosphere is remarkably like Earth's, but even more complex and multilayered, according to results from the European Space Agency’s Huygens probe.

The lander also saw signs of lightning and found chemical clues to the source of Titan's methane, which probably bubbles up from deep inside Saturn’s giant moon.

Titan is the only satellite in the solar system to have any appreciable atmosphere. It is mainly nitrogen, like Earth’s air, but it is 10 times as dense as our terrestrial atmosphere. As a result, the parachute-braked descent of Huygens to the surface in January took a leisurely 2.5 hours, giving it ample time to sample the gases around it.

The atmosphere turns out to be an exotic layer-cake. It has a troposphere and stratosphere, as on Earth, divided by a boundary called a temperature inversion. But much further out – 500 kilometres above the surface and higher – Huygens’ Atmospheric Structure Instrument (HASI) detected many more such inversions, each defining their own narrow atmospheric layer.

That is unlike Earth, says Marcello Fulchignoni, head of the HASI team. But it comes as no great surprise, because Titan's atmosphere is so much thicker. Fulchignoni thinks that some of these upper layers may be quite stable and may undulate in great slow waves, driven by Saturn's gravity.

Dead calm
Down below, a thick layer of orange smog clings to the top of the stratosphere, 200 to 250 kilometres up, and there is a thinner layer of haze at an altitude of about 20 km.

In between the two, Huygens entered an unexpected zone. Mission scientists found that Titan's fierce winds die down rapidly below a height of 100 km. At 80 km there is almost a dead calm, but then as the probe fell further the winds rapidly strengthened to a bracing 140 km/hour. The team have no explanation yet for Titan's doldrums.

A little lower down, HASI picked up several bursts of electrical activity, possibly echoes of lightning elsewhere on Titan. The electrical waves had a frequency of about 36 hertz – a very low rumble. But Fulchignoni is cautious. "It could be an indication of lightning, but maybe the discharge is due to something inside the probe," he says.

Any lightning would probably be generated in clouds of methane, the gas that forms about 5% of Titan's atmosphere. It seems to play an analogous role to water on Earth, raining down to carve branching drainage patterns in the hills.

But the very presence of methane is a puzzle – it is destroyed in the stratosphere by sunlight, forming the orange smog of more complex organic molecules which eventually settles to the ground. This mean the methane is being replenished from an unknown source.

Volcanic eruptions
A clue comes from another Huygens instrument – its Gas Chromatograph Mass Spectrometer (GCMS) – which has detected a telltale variety of argon. Argon-40 is generated by the radioactive decay of potassium-40, present in Titan's rocky core.

To reach Titan's atmosphere, the argon must have got through the ice crust, presumably in some kind of volcanic eruption – so the methane could be coming out that way too.

The GCMS team suggest two possibilities. Methane might be constantly generated by chemical reactions in the core. Or it might be stored in a great reservoir under the crust, as a methane-water ice.

http://www.newscientistspace.com/article.ns?id=dn8395
 
The ESA website has the best summary of the latest results from Huygens:

link
 
Rivers On Titan, One Of Saturn's Moons, Resemble Those On Earth


Recent evidence from the Huygens Probe of the Cassini Mission suggests that Titan, the largest moon orbiting Saturn, is a world where rivers of liquid methane sculpt channels in continents of ice. Surface images even show gravel-sized pieces of water ice that resemble rounded stones lying in a dry riverbed on Earth.
But with a surface temperature of minus 179 degrees Celsius and an atmospheric pressure 1 1/2 times that of Earth, could fluvial processes on Titan be anything like those on Earth?

"The idea that rivers of methane moving chunks of ice on Titan ought to obey the same rules as rivers on Earth is not what you would assume at first," said Gary Parker, the W. H. Johnson Professor of Geology and a professor of civil and environmental engineering at the University of Illinois at Urbana-Champaign.

"However, if river dynamics are truly understood at a physical level, then relations that provide reasonable results on Earth ought to provide similarly reasonable results on Titan."

Parker, who has collected data from rivers all over the world, has calculated what should be key similarities and key differences between river networks on Earth and Titan.

There are only three parameters that differ significantly between Earth and Titan, Parker said. First is the acceleration due to gravity - on Titan it is about one-seventh the value on Earth. Second is the viscosity of flowing fluid - the viscosity of liquid methane on Titan is about one-fifth that of water on Earth. Third is the submerged specific gravity of sediment - the value on Titan is about two-thirds of that on Earth.

"What this means is that for the same discharge of liquid methane as to water, the channel characteristics on Titan should be remarkably similar to those on Earth," Parker said. "However, because of the smaller acceleration due to gravity, channel slopes on Titan should be wider, deeper and less steep than those on Earth."

Wildcards that make Parker's predictions tentative include a freeze-thaw process of methane that might not be analogous to the freeze-thaw process of water on Earth, and the formation of hydrocarbons on Titan that might add a kind of cohesion not encountered on Earth.

"The interaction of sunlight with a hydrocarbon rich atmosphere could possibly precipitate very sticky compounds that could give streams on Titan a degree of cohesion that makes them behave differently," Parker said.

If the underlying physics has been captured correctly, Parker's correlations could be used to predict river features not just on Earth and Titan, but elsewhere as well; revealing the internal consistency of fluvial processes at work under vastly different conditions.

"We are now receiving images from Mars that show relic rivers. But these analogues to what has happened on Earth are very, very old and the processes may not have been very strong," Parker said. "What is happening on Titan, however, may be every bit as active and exciting as what is happening on Earth."

http://www.spacedaily.com/news/saturn-titan-05zo.html
 
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