High Hopes For Cassini's Titan Fly-by

Rubyait

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Cassini lines up close moon flyby


The Cassini spacecraft is heading towards its closest encounter with the Saturnian moon known as Enceladus.
It will pass a mere 175km (109 miles) from the surface of the icy body on Thursday, taking images and readings.

Enceladus has grown in interest since the US-European mission to the Saturn system arrived just over a year ago.

Cassini recently discovered a thin but significant atmosphere around the moon, which many scientists suspect may harbour ice volcanoes and geysers.

The atmosphere, composed of ionised water vapour, was detected by the orbiter's magnetometer instrument during flybys in February and March.

In those close encounters, Cassini's cosmic dust analyser also detected a shroud of icy particles around the moon.

Icy puzzle

Researchers are keen to follow up both these findings because they hint at previously unobserved activity on the satellite, where temperatures go down to -180C.

Enceladus measures some 500km (310 miles) in diameter and is described as the most reflective object in the Solar System, throwing back about 90% of the sunlight that hits it.

Orbiting Saturn at a distance of approximately 237,400km (147,500 miles), it sits in the middle of the outermost ring - the E ring.

This is composed of tiny ice particles that only last for hundreds of years. So, researchers believe there has to be a source of them and that source is most probably Enceladus.

Likewise, with the atmosphere, Enceladus does not possess the gravitational attraction necessary to hold on to a cloud of water ions, so this must be being replenished also.

Four-year low

Ice volcanoes would be a compelling solution to the puzzle and the continuous deposition on the surface of icy particles might explain the high reflectivity of Enceladus

Dark spots previously pictured on the surface may mark places of upwelling or outgasing.

Theoretical study, too, has suggested where the energy comes from to drive activity: from tidal heating as Saturn's gravitation field pulls on Enceladus as it moves around an eccentric orbit.

"But this is all speculation right now; all we have is the circumstantial evidence," said Cassini imaging scientist Professor Carl Murray of Queen Mary, University of London, UK.

"As yet, we haven't seen any activity. We've seen these dark spots on the surface and these are perhaps points of weakness where material comes out. But even if it is active, Enceladus may not be active right now. It's all a bit of a puzzle," he told the BBC News website.

The 14 July encounter was to have been at an altitude of 1,000km (620 miles), but the mission team has become so intrigued by the moon that a decision was taken to lower the height of the pass.

In fact, Thursday's encounter will be Cassini's lowest-altitude flyby of any object during its nominal four-year tour.

The $3.2bn Cassini-Huygens mission is a joint venture between the US space agency (Nasa), the European Space Agency (Esa) and the Italian Space Agency (Asi).

http://news.bbc.co.uk/1/hi/sci/tech/4676069.stm
 

Rubyait

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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
 

Rubyait

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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
 

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Not Titan but the Cassini probe has taken images of Enceladus.

Saturn moon delights and baffles


Space scientists say their discoveries about Saturn's moon Enceladus are stunning, if just a little baffling.

Using the instrument-packed Cassini probe, they have confirmed that the 500km-wide world has an atmosphere.

They have also seen a "hotspot" at the icy moon's south pole, which is riven with cracks dubbed "tiger stripes".

But the US and European scientists told a London meeting they could not yet explain fully the energetic processes driving all the activity on Enceladus.

"There were signs from a long time ago that Enceladus was a strange moon," said Dr Carolyn Porco, leader of Cassini's imaging team, "but it is just so gratifying and fabulous to see all the results come together and clearly point to a specific region on the surface which seems to be the origin of a lot of that peculiarity."

'Strange' world

The moon has become a major target of interest since the Cassini mission to the Saturn system arrived just over a year ago.

Enceladus orbits the ringed planet at a distance of approximately 237,400km and is described as the most reflective object in the Solar System; its icy surface throws back about 90% of the sunlight that hits it.

The spacecraft made a special low pass of the moon on 14 July, crossing a mere 173km above the surface at its closest approach.

This allowed Cassini to make observations of unprecedented detail; and they backed up data obtained by the probe's magnetometer instrument on previous flybys that hinted at the presence of a water vapour atmosphere.

But that was just the start of what is now proving to be a fascinating and evolving story.

"We confirmed the signature that there was an atmosphere but it is strange atmosphere," Professor Michele Dougherty, from the UK's Imperial College and the lead scientist for the magnetometer instrument, told BBC News.

"It seems to be concentrated at the south pole and the best way to match our observations is that you have almost a cometary jet coming off the south pole."

'Hard to understand'

High-resolution imagery shows the southern polar region to be relatively smooth - usually a good indicator of recent activity - but cut by a number of long, dominant cracks. These are the so-called tiger stripes.

They are about 130km long and roughly parallel to one another, spaced about 40km apart.

Cassini's composite infrared spectrometer shows the region to be much warmer than expected.

Whereas temperatures near the equator are a frigid 80 Kelvin (minus 193C), the south polar average reaches 85K (minus 188C). Small areas of the pole, concentrated near the tiger stripe fractures, are even warmer: well over 110K (minus 163C) in some places.

"The amount of heat there is really hard to understand as being due to just sunlight warming the surface," said Dr John Spencer, from the Southwest Research Institute in Colorado, US.

"It shouldn't be that warm at the pole. It would be like flying past the Earth and finding that Antarctica was warmer than equatorial regions - that strange.

"This is only the second place in the Solar System beyond Earth that we've seen signs of heat coming out of the interior - the other being Jupiter's moon Io."

The scientists think the cracks may act like vents, spewing out water vapour and very fine water-ice particles. Some have suggested there could be ice geysers and even ice volcanoes at the stripe locations - but these have not been imaged directly.

Interest index

The puzzle for researchers is how to explain such an energetic system on Enceladus.

As the moon moves around an eccentric orbit of Saturn, gravitational forces should subject the tiny world to some tidal heating. Radioactive isotopes in its rocky core may also be a source of some warming.

But scientists are struggling to make the numbers add up and are frankly baffled as to why the activity they see should be so concentrated in just the one region.

"One of the most fascinating aspects of Enceladus is that it's so very small as icy moons go, but so very geophysically active," said Dr Bob Brown, from the University of Arizona, US, and team leader for Cassini's visual and infrared mapping spectrometer.

"It's hard for a body as small as Enceladus to hold onto the heat necessary to drive such large-scale geophysical phenomena, but it had done just that.

"Enceladus and its incredible geology is a marvellous puzzle for us to figure out."

Certainly, what the Cassini data has done is thrust Enceladus up the interest index of objects in the Solar System that demand further investigation.

Scientists may not be able to explain the "boiler" at the south pole but they are already talking up the possibility that conditions there could allow for liquid water below the surface - with all the implications that might have.

"It's quite likely that this moon will now join the ranks of Mars and Jupiter's moon Europa where you might have liquid water - and the biologists could start getting interested in this being a place were life might possibly arise," enthused Dr Torrence Johnson, a Cassini scientist from Nasa's Jet Propulsion Laboratory in California.

"It moves Enceladus from being a small denizen of the outer Solar System - a frozen iceberg - to something that's more of an active type world that we're interested in exploring."

Cassini discoveries at Enceladus include:

presence of a strange atmosphere concentrated at the south pole
atmosphere mostly (91%) water vapour, but with some nitrogen, carbon dioxide and other simple carbon-based molecules (organics)
large crevasse features at south pole dubbed tiger stripes
intriguing hotspot at south pole - anomalous warmth in the area of the tiger stripes
presence of "orderly" water-ice at south pole, especially within tiger stripe features, indicates region must have been very hot, be very young, or both
presence of simple organics along the fractures
indication that water vapour and fine material are being ejected from tiger stripes
fine ice material is probably the significant and sustaining source of ice particles that make up Saturn's outermost ring - its E ring
Cassini scientists are meeting in London this week ahead of a major conference of the American Astronomy Society in Cambridge next week.
The $3.2bn Cassini-Huygens mission is a joint venture between the US space agency (Nasa), the European Space Agency (Esa) and the Italian Space Agency (Asi).

http://news.bbc.co.uk/1/hi/sci/tech/4197686.stm

 

Rubyait

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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
 
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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
 

Rubyait

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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
 
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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
 

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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."
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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.

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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
 

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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
 

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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
 

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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
[/b]
 

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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
 

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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
 
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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
 
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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
 
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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
 
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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
 

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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
 

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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
 

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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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Cassini Images Reveal Spectacular Evidence Of An Active Moon


Jets of fine, icy particles streaming from Saturn's moon Enceladus were captured in recent images from NASA's Cassini spacecraft. The images provide unambiguous visual evidence that the moon is geologically active.
"For planetary explorers like us, there is little that can compare to the sighting of activity on another solar system body," said Dr. Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colo.

"This has been a heart-stopper, and surely one of our most thrilling results."

The Cassini images clearly show multiple jets emanating from the moon's south polar region. Based on earlier data, scientists strongly suspected these jets arise from warm fractures in the region. The fractures, informally dubbed "tiger stripes," are viewed essentially broadside in the new images.

The fainter, extended plume stretches at least 186 kilometers (300 miles) above the surface of Enceladus, which is only 186 kilometers wide. Cassini flew through the plume in July, when it passed a few hundred kilometers above the moon.

During that flyby, Cassini's instruments measured the plume's constituent water vapor and icy particles.

Imaging team members analyzed images of Enceladus taken earlier this year at similar viewing angles. It was a rigorous effort to demonstrate that earlier apparitions of the plumes, seen as far back as January, were in fact real and not due to imperfections in the camera.

The recent images were part of a sequence planned to confirm the presence of the plumes and examine them in finer detail. Imaging team member Dr. Andrew Ingersoll from the California Institute of Technology, said, "I think what we're seeing are ice particles in jets of water vapor that emanate from pressurized vents. To form the particles and carry them aloft, the vapor must have a certain density, and that implies surprisingly warm temperatures for a cold body like Enceladus."

Imaging scientists are comparing the new views to earlier Cassini data in hopes of arriving at a more detailed, three-dimensional picture of the plumes and understanding how activity has come about on such a small moon. They are not sure about the precise cause of the moon's unexpected geologic vitality.

"In some ways, Enceladus resembles a huge comet," said Dr. Torrence Johnson, imaging team member from NASA's Jet Propulsion Laboratory.

"Only, in the case of Enceladus, the energy source for the geyser-like activity is believed to be due to internal heating by perhaps radioactivity and tides rather than the sunlight which causes cometary jets." The new data also give yet another indication of how Enceladus keeps supplying material to Saturn's gossamer E ring.

Cassini's Photo Album From A Season Of Icy Moons
Pasadena CA (JPL) Dec 07 - Wrapping-up a phenomenally successful year of observing Saturn's icy moons, the Cassini mission is releasing a flood of new views of the moons Enceladus, Dione, Rhea, Hyperion, and Iapetus.

The moons and their intricacies are being highlighted today at a news briefing held today at the American Geophysical Union meeting in San Francisco, Calif.

Several new images of Rhea, a moon measuring 1,528 kilometers (949 miles) across, were taken during Cassini's most recent close flyby on November 26. During the encounter, Cassini dipped to within 500 kilometers (310 miles) of Rhea's surface.

Additional new images include two "zoomable" mosaics of Rhea and Hyperion at high resolution; false-color views revealing compositional variation on the surfaces of Hyperion, Dione and Rhea; two movies reproducing Cassini's exciting encounters with Iapetus and Hyperion; and dazzling new images of the plumes of Enceladus, including a time-lapse movie.

http://www.spacedaily.com/news/cassini-05zzzzd.html
 

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Huygens Finds A Hostile World On Titan


Conditions on Saturn's moon Titan, with its dense atmosphere, are similar to those on Earth early in our solar system. Pictures and spectral analysis of Titan's surface, recorded by an international scientific team including researchers from the Max Planck Institute for Solar System Research (MPS), show a dried-out "river" landscape.
Evaluating the data has now shown that methane on Titan exists in solid, liquid, and gas states, and plays a similar role in Titan's atmosphere and on its surface that water plays on Earth. Water ice on Titan congeals to be similar to stone on Earth: it makes up a major component of the Titan's surface. "Stones" made presumably largely of water ice show signs of erosion and transport through a liquid. (Nature, Advanced Online Publication, November 30, 2005).

With a diameter of about 5,150 kilometres, Titan is the largest moon of Saturn. It has a dense atmosphere which we mostly cannot see through. Until recently, Titan was one of the few objects in the solar system whose surface was not researched. In 1997, the Cassini/Huygens mission to Saturn was launched.

The NASA spaceship Cassini reached Saturn's orbit in 2004 and since then has been investigating the ringed planet and its moons. The Huygens probe of the European Space Agency ESA separated from Cassini at the end of 2004 and landed on Titan on January 14, 2005, after a two-and-a-half hour descent through the atmosphere.

Among the scientific instruments aboard Huygens were the Descent Imager/Spectral Radiometer (DISR), plus a combination of 14 cameras, spectrometers for visible and infrared light, and photometers. The Max Planck Institute for Solar System Research developed the CCD detector, which received the signal from all the cameras and spectrometers in the visible wavelengths.

During descent, as well as after Huygens landed, the DISR investigated the atmosphere and surface of Titan. At first sight, it is similar to a landscape on Earth. We can see the courses of rivers, which lead from a higher-lying area to a lower, flat terrain, bordered by a kind of coastline (see image 1). Spectral analysis showed indeed that materials from the higher areas were transported down to a "sea".

Huygens landed in the low-lying, flat area. The pictures taken after landing (see image 2) show that there is currently no liquid in the "sea". There are, however, "stones", whose rounded shape, and size distribution, suggest they were transported in a liquid. Given the extremely low temperatures on Titan -- about 180 degrees below Celsius -- the liquid could not be water. The scientists guess rather that it is methane and/or another hydrocarbon, and that the "stones" are made of water ice.

Investigations of the atmosphere on Titan concentrated on its dust layer. Before landing, it was assumed that the dust is only located above 50 kilometres up in the atmosphere, and the area lying underneath it is clear. The DISR measurements have now shown that the dust layer reaches down to the surface. Spectral analysis shows that the dust particles are aggregates of some hundreds of very small particles, about 50 nanometers across. Original work:

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

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Cassini Significant Events 12/21/05 - 01/04/06


The most recent spacecraft telemetry was acquired Wednesday, January 4, from the Goldstone tracking stations. The Cassini spacecraft is in an excellent state of health and is operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" web page located at http://saturn.jpl.nasa.gov/operations/p ... sition.cfm .

Cassini Significant Events 12/21/05 - 01/04/06

Due to the holidays, no Significant Events report was generated last week. The report this week covers 15 days from December 21, 2005 through January 4, 2006. Hang on, it's gonna be a long report!

Wednesday, December 21 (DOY 355):

Uplink Operations personnel sent commands to the spacecraft today to perform an on-board live Inertial Vector Propagation (IVP) update. The update will execute on DOY 358/359 and will update vectors for Dione, Tethys, Enceladus, Saturn, and Telesto.

Science activities today included a distant observation of Hyperion involving all Optical Remote Sensing (ORS) instruments, and Imaging Science Subsystem (ISS) tracks of many small moons as part of the Satellite Orbit Determination Campaign.

Thursday, December 22 (DOY 356):

A preparation meeting was held today for Orbit Trim Maneuver (OTM) 047. The maneuver is scheduled to execute on December 29.

Friday, December 23 (DOY 357):

The RADAR instrument performed an engineering test that will address radiometer calibration issues using Saturn as a reference target.

Saturday, December 24 (DOY 358):

Today marked the start of the annual sequence development hiatus. The Aftermarket, Science Operations Plan Update (SOPU), and Science and Sequence Update Process will pause activities from today through January 2, 2006. The processes will begin again on January 3. Early on in the tour, program management identified the difficulty of trying to conduct this type of development over the Christmas and New Year's holidays due to varying vacation schedules and the different holiday schedules of our foreign partners. As a result, each year a pause is built in to the development schedules that lasts for about two weeks during this time. Operations work continues, OTMs, real time commanding, downlink, etc. It's just these three processes that pause. Well, OK, we do cancel a few meetings:)>)

Non-targeted flybys of Enceladus and Pallene occurred today. The Enceladus flyby was at an altitude of 93,984 km.

Whoa. It's been a year. Today is the one-year anniversary of the Huygens Probe release! For those of you who would like to remember where we were last year at this time, here is an extract from the Significant Events report for December 24, 2004, Christmas Eve:

Everything looks good and nominal.

JPL provided dinner for those of us who had to work. There was slight congestion at the dessert table, but everything else was nominal.

All Orbiter instruments reported in. Everyone is in the correct configuration and is ready for release.

The project set up a conference line so that Cassini flight team members who are not working the event but who came in anyway to show their support can listen in on events as they unfold.

The Huygens Probe was successfully deployed from the Cassini Orbiter! Navigation and Spacecraft Operations Office teams confirmed the nominal separation of the Probe at 7:24 Pacific time. The Probe is now in free flight at a spin rate of 7.5 rpm as detected by the Magnetometer Subsystem. All systems performed as expected, there were no problems reported with the Cassini spacecraft, no red alarms, no fault protection. Congratulations everyone!

After release, the Uplink Operations (ULO) sequence lead called for the start of planned Probe optical navigation imaging. This is a 4.5 hour process. Currently we are on schedule.

The head of the Huygens Spacecraft Operations Unit expressed his thanks to the team for a wonderful adventure in the exploration of Saturn. Huygens personnel are now waiting with great expectation for the Probe descent on January 14, 2005.

Sunday, December 25 (DOY 359):

Non-targeted flybys of Helene and Telesto occurred today.

Science activities today included a Composite Infrared Spectrometer (CIRS) Saturn Tethys F-Ring movie, and the first of three Radio Science Subsystem (RSS) Gravity Science Enhancement passes on and after Christmas - DOY 359, 361, and 362. These are additional downlink passes at Ka-band to obtain Titan gravity science.

Monday, December 26 (DOY 360):

On December 26, Cassini flew by Titan at an altitude of 10,409 kilometers. At this time, the Imaging Science Subsystem (ISS) acquired a mosaic of Titan's albedo features Aztlan and Quivira, Bazaruto and Elba Faculae, and Omacatl Macula, at low phase angles of approximately 25 degrees and pixel resolution scales of approximately 700 to 450 meters. This ISS observation also overlaps eastern portions of the Titan A and Titan 3 RADAR swaths. The Composite Infrared Spectrometer (CIRS) obtained information on trace constituents in Titan's stratosphere. An integration of the limb obtained information on CO, HCN, and CH4. The Ultraviolet Imaging Spectrograph (UVIS) used its Hydrogen-Deuterium Absorption Cell (HDAC) to conduct key measurements of the Titan atmosphere as well. Measurements of the D/H ratio in the Titan atmosphere will yield clues to the formation and history of Titan and the Saturnian system. The Visual and Infrared Mapping Spectrometer (VIMS) also obtained a medium resolution regional map using the same observing strategy as the previous Titan flyby.

Moreover, this Titan flyby presented an excellent diametric wake crossing at 5.04 Titan radii downstream for all of the Magnetospheric and Plasma Science (MAPS) instruments, which will be ideal for comparisons to the Voyager-1 Titan flyby data set. Cassini's encounter possessed similar observing geometry as the encounter of Voyager-1 in November 1980. Especially with the increased capability of Cassini, the MAPS instruments will finally be able to compare the Cassini and Voyager data sets to further study Titan's atmospheric loss and the structure of Titan's plasma wake. But more importantly, this flyby will represent the only crossing of Titan's magnetotail at an intermediate distance in the Cassini tour, which will be highly valuable for the study of the formation of Titan's magnetotail as a function of distance.

Tuesday, December 27 (DOY 361):

It was reported today at the weekly Operations Status and Coordination meeting that data from the Titan 9 flyby yesterday has been successfully downlinked. In particular UVIS reported that they had received the entire HDAC observation data set. There were several gaps of less than one minute due to some problems at DSS-14, but nothing that required the implementation of the contingency plans and procedures that had been developed and reported on last week.

Wednesday, December 28 (DOY 362):

An article was presented in the December 27 Aerospace Daily & Defense Report stating that NASA is considering a two-year extension to the Cassini mission that would extend the exploration of Saturn and its moons through 2010. "NASA has given us some additional funding to study what the options would be" for the extra two years, said Bob Mitchell, Cassini program manager at the Jet Propulsion Laboratory in Pasadena, Calif. The spacecraft's lifetime ultimately will be determined by what kind of follow-on mission, if any, is carried out. "If we put together a tour that would look very much like what we're doing now - a Titan flyby every month or so and an icy satellite flyby stuck in here and there - then another two years would probably about run us out of propellant. However, if the spacecraft is placed in a fairly uneventful orbit and dedicated to studying Saturn's ring system, for example, it could likely last years longer." he said.

Thursday, December 29 (DOY 363):

OTM-047 was successfully performed today. This was the cleanup maneuver from the Titan-9 flyby that occurred on December 26. The reaction control subsystem (RCS) burn began at 7:55 pm Pacific Time. Telemetry obtained immediately after the maneuver showed the burn duration was 198.9 seconds, giving a burn delta-V of 0.179 m/s. All subsystems reported nominal performance after the OTM.

Beginning today and running through January 4, science activities involve the entire suite of MAPS instruments simultaneously performing low-rate outer magnetospheric surveys to observe the variability of magnetospheric boundaries at a variety of radial distances. Optical remote sensing activities include ISS observations of a mutual event capturing Janus crossing Dione, many photometric calibrations done with a variety of stars, and narrow-angle camera lightning searches in Saturn's northern hemisphere. Finally, UVIS will obtain mosaics of Saturn's inner magnetosphere.

Friday, December 30 (DOY 364):

Today is the fifth anniversary of the Cassini flyby of Jupiter on December 30, 2000.

Saturday, December 31 (DOY 365):

Documenting a year at Saturn, Astronomy Picture of the Day selected for their picture today an image of Saturn's moon Dione in front of edge-on rings and the cloud tops of Saturn draped with broad ring shadows. It's very cool!

2006

Sunday, January 1 (DOY 001):

This feels more like a Christmas present than a report of what to expect in the New Year! In 2006 Cassini will execute all or part of 10 on-board sequences from S17 through S26, and all or part of 18 orbits of Saturn from Rev 19 through Rev 36 will occur. During this time there will be 13 targeted flybys of Titan including T10 through T22, 20 non-targeted flybys including Helene, Rhea, Polydeuces, Tethys, Telesto, Titan, Atlas, Calypso, Enceladus, Methone, and Dione, 39 opportunities for maneuvers from OTM-048 through OTM-086, the start of extended mission development will begin in January, one superior conjunction will occur in August, and finally a partridge in a pear tree will occur next December. :)>). Should be a busy year.

Monday, January 2 (DOY 002):

OTM-48, originally scheduled for today, was cancelled back in early November along with OTM-54 and OTM-60. This was done because there were only three DSN tracks between the cleanup and apoapsis maneuvers, delivery errors did not improve after the apoapsis maneuver, and the maneuvers would be difficult to cancel in real time. The delta-V cost was about 0.8 m/sec. The capability to execute a maneuver on the planned prime and backup passes was retained but proved unnecessary for OTM-048. Spacecraft Operations and Navigation will re-evaluate OTMs 54 and 60 as necessary.

Tuesday, January 3 (DOY 003):

Dark terrain on Iapetus was selected as Astronomy Picture of the Day today.

Flight software (FSW) normalization for CIRS and the Cassini Plasma Spectrometer (CAPS) was begun today and will continue through January 6. There are four copies of an instrument's FSW in partitions 0 through 3 on each SSR. When the instrument team has a new version of FSW, it is uploaded into 2 of the partitions, in this case partitions 2 and 3, leaving copies of the old software on 0 and 1. The old version is retained until the instrument team performs a flight software checkout and confirms the new version. After the confirmation, "normalization" is performed where the new version replaces the old version in the remaining partitions on both SSRs, in this case 0 and 1.

Wednesday, January 4 (DOY 004):

The Science Operations Plan Update process for S20 kicked off today. The process will run for five weeks and will conclude on February 10.

Wrap up:

Check out the Cassini web site at http://saturn.jpl.nasa.gov for the latest press releases and images.

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 Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter.

http://saturn.jpl.nasa.gov/news/sig-eve ... newsID=625
 

Rubyait

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A return to the orangey world

It had this strange orange-yellow hue and the focussing was some way off pin-sharp, but the image returned from the surface of Titan by the Huygens probe was unquestionably one of the pictures of 2005.

Twelve months on, and you still look at it with wonder - what lies to the right or left, just out of view? What's behind?

All we got was the one shot; so, those questions will for ever be left hanging.

It seems remarkable - to this correspondent at least - that you can get any sort of picture from the surface of a moon that's more than a billion km from Earth.

Mind you, not everyone was impressed. A few newspapers remarked on the picture's mundaneness. "Is that all?" they asked; "It looks like a beach on Earth."

One columnist even suggested the public had become bored with fuzzy space images and jokingly suggested that only a Frisbee-catching dog running in the background could have piqued people's interest.

Not for John Zarnecki, the principal investigator on the science payload sent with Huygens to investigate Titan's surface. He continues to marvel at that picture and is staggered by the probe's achievements.

"It's still not long enough for me to be able to look back in a detached way," the Open University professor told the BBC News website.

"People tend to think that it happens, you do the analysis and that's it. Not so; we're still deep in it."

'Technology tallpoles'

Indeed, the data returned by the robot probe as it floated down through the moon's thick atmosphere to land on a pebble-strewn terrain will keep researchers busy for years.

Titan lived up to expectations; the photochemical haze that shrouds its surface was finally lifted.

Huygens showed us a frozen world that seemed to resemble a primitive Earth - it was somehow very familiar but also very alien.

The rocks are really ice and the rain that falls in a good breeze is made of liquid methane, not water.

The probe spied channels and basins that looked as though they had been cut by rivers, and the surface itself appeared to be covered in a "wet" sand that threw up a plume of methane as the warm robot touched down.

"We actually think we hit one of those pebbles as we landed," said Zarnecki. "If you look at that orangey picture, look at the bottom-left - one of the pebbles is broken. We'll never know for sure but that might have been the one we bashed and broke in two."

However big the data return, there are always going to be more questions than answers; and the desire to go back will get ever stronger.

It won't happen for another 10 years or so. The scientific community has its eye next on Europa, the icy moon of Jupiter; but that does not mean researchers have put aside thoughts of a follow-up - far from it.

The US space agency (Nasa), for example, has teams who conceptualise future missions.

"We try to understand what can and cannot be done; what are the technological tallpoles, and from these kind of studies we can see what needs to be developed and that feeds into our programmes," explains Dr Tibor Balint, from the Jet Propulsion Laboratory in Pasadena.

Power issue

Balint's team has recently worked through the engineering challenge of putting a rover on Titan. The group envisioned a vehicle that looked much like the robot explorers despatched to Mars.

Obvious comparisons include the mast-mounted camera system and the robotic arm that can reach out to take measurements or bring back samples to an instrument carousel.

Unlike the Mars rovers' six-wheel configuration, the Titan concept would use just four large wheels.

"When you get down to the surface, you fold the wheels out, inflate them and you can have a much larger surface coverage," Dr Balint told me. "These wheels are 1.5m in diameter and over a three-year operation you could cover up to 500km."

Perhaps the biggest difference to the Mars machines, though, is the power source.

The Mars rovers have a deck of solar cells to top their batteries. Being positioned so far from the Sun and hidden under a deep column of haze, the Titan rover would need a radioisotope thermoelectric generator (RTG).

This type of generator creates electricity from heat given off by the natural decay of plutonium. The US has long experience of using RTGs in space: the 1970s Viking landers on Mars were powered in this way, as is Huygens' mothership, Cassini.

The Titan explorer would trundle over those orange pebbles looking for "lakes" of methane, and studying the surface composition and chemistry.

It is an enticing prospect but it is not the only option being considered. Another JPL team has been looking into the idea of putting a 15m-long, helium or hydrogen-filled blimp on Titan.

In the dark

A balloon can cover far greater distances than a rover and the conditions on the Saturnian moon would be ideal: a dense atmosphere, low gravity and only gentle winds (walking pace) at the surface.

Current designs call for two larger propeller engines to drive the airship forward and two smaller props at the rear to control pitch and yaw.

A gondola could be slung beneath the envelope to carry the instrument suite and a RTG that would provide that all important power.

But there is a significant challenge in operating such a vehicle so far from Earth.

"The round trip light-time is 2.6 hours; that's a lot worse than talking to the rovers on Mars," explains team member Alberto Elfes.

"In addition to that, depending on the relative positions of Titan, Saturn and Earth, you may have situations where you have blackout periods of up to 16 days or so.

"Under those conditions, you need a vehicle that is substantially autonomous, that can take care of itself."

Elfes and colleagues have tested an artificial intelligence system on a small airship over a dry lake bed in El Mirage, California. The vehicle was able to navigate itself to designated waypoints, correcting its path to take account of the wind.

Take this sophistication to another level and an aerobot sent to Titan could be left to get on with scientific observations, safe in the knowledge that the vehicle would not crash into the first hill.

Alien waves

Dr Elfes sees a Titan blimp working close to the surface, possibly firing tethered, harpoon-like probes into the ground to grab samples for study.

"You collect a small amount of material, release the [harpoon] mechanism on the surface and haul up the small, thimble full of material to be analysed onboard," he said.

"We have looked at designs that would have 12 to 24 of these throwaway probes that would be used as you go from one interesting site to another."

John Zarnecki favours an aerial mission but he also rather likes the idea of combining it with a mini-rover. The airship would first survey the most interesting sites and then unleash a wheeled vehicle to get in amongst those pebbles.

"I definitely want to go back," he said. "I'd love to see the lakes that must be there some times - lakes of liquid hydrocarbons. I'd love to see a lake with some gentle waves lapping on the shore.

"These physical processes are so familiar on Earth but we've never seen them in a different parameter space - one-seventh gravity with liquid methane instead of water. It would be mind-blowing."

http://news.bbc.co.uk/1/hi/sci/tech/4610792.stm
 
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