Saturn, its rings and moons small to large in this Cassini image. Credit: NASA/JPL/Space Science Institute
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This latest offering from the Cassini spacecraft shows a wide-angle view of Saturn, its rings, and a sampling of the planet’s moons in varying sizes. Saturn’s largest moon, Titan, is in the center of the image, with the smaller moon Enceladus on the far right, while appearing just below the rings on the far left beyond the thin F ring is teeny-tiny Pandora. Oh, to have this view out your spacecraft window as you approach the ringed-world for a flyby!
How do the moons shown here vary in size? Titan is 5,150 kilometers, or 3,200 miles, across. Enceladus is 504 kilometers, or 313 miles across, while Pandora is 81 kilometers, or 50 miles across. This view looks toward anti-Saturn side of Titan and toward the northern, sunlit side of the rings from just above the ringplane.
The image was taken with the Cassini spacecraft wide-angle camera on Jan. 15, 2011, from a distance of about 844,000 kilometers (524,000 miles) from Titan. Image scale is 50 kilometers (31 miles) per pixel.
Titan peeks from behind two of Saturn's rings. Another small moon Epimetheus, appears just above the rings. Credit: NASA/JPL/Space Science Institute
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It seems Titan is getting more Earth-like all the time. There are lakes, rainfall (never mind that any liquids on Titan are frigid hydrocarbons), dust storms, lightning and all sorts of other activity going on it the atmosphere, along with clouds. And now, not just any clouds but cirrus clouds, very similar to what we have on Earth: thin, wispy clouds of ice particles high in the atmosphere. A team of researchers at NASA’s Goddard Space Flight Center say that unlike Titan’s brownish haze, the ice clouds are pearly white.
“This is the first time we have been able to get details about these clouds,” said Robert Samuelson, an emeritus scientist at Goddard and the co-author of a new paper published in the journal Icarus. “Previously, we had a lot of information about the gases in Titan’s atmosphere but not much about the [high-altitude] clouds.”
Using the Composite Infrared Spectrometer (CIRS) on NASA’s Cassini spacecraft scientists can get a “weather report” of sorts. Previously, scientists have found that Titan’s intriguing atmosphere has a one-way cycle that delivers hydrocarbons and other organic compounds to the ground as precipitation.
Those compounds don’t evaporate to replenish the atmosphere, but somehow the supply has not run out.
Additionally, puffy methane and ethane clouds had been found before by ground-based observers and in images taken by Cassini. But these new clouds are much thinner and located higher in the atmosphere.
“They are very tenuous and very easy to miss,” said Carrie Anderson, the paper’s lead author. “The only earlier hints that they existed were faint glimpses that NASA’s Voyager 1 spacecraft caught as it flew by Titan in 1980.”
So what are these cirrus clouds made of?
This mosaic of Titan was created from the first flyby of the moon by Cassini in 2004. Credit: NASA/JPL/SS
More than a half-dozen hydrocarbons have been identified in gas form in Titan’s atmosphere, but many scientists feel there are probably many more that haven’t yet been identified.
The clouds on Titan can’t be made from water because of the planet’s extreme cold. “If Titan has any water on the surface, it would be solid as a rock,” said Goddard’s Michael Flasar, the Principal Investigator for CIRS.
Instead, the key ingredient is likely methane. High in the atmosphere, some of the methane breaks up and reforms into ethane and other hydrocarbons, or combines with nitrogen to make materials called nitriles. Any of these compounds can probably form clouds if enough accumulates in a sufficiently cold area.
To find these cloud, the team focuses on the observations made when CIRS is positioned to peer into the atmosphere at an angle, grazing the edge of Titan. This path through the atmosphere is longer than the one when the spacecraft looks straight down at the surface. Planetary scientists call this “viewing on the limb,” and it raises the odds of encountering enough molecules of interest to yield a strong signal.
So, when the researchers look at the data, they can separate the telltale signatures of ice clouds from the other aerosols in the atmosphere. “These beautiful, beautiful ice clouds are optically thin, and they’re diffuse,” said Anderson. “But we were able to pick up on them because of the long path lengths of the observations.”
A close look at Enceladus, with Saturn's rings in the background. Credit: NASA/JPL/Space Science Institute
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The Cassini spacecraft has taken a some recent images of two of Saturn’s most notorious moons, where in both images the planet’s rings serve as a backdrop. Above, Enceladus stands out with its cratered surface, but Cassini’s camera also catches a glimpse of the planet’s rings in the background. Geologically young terrain in the middle latitudes of the moon shifts to older, cratered terrain in the northern latitudes.
The image was taken during the spacecraft’s flyby of Enceladus on Nov. 30, 2010, in visible with Cassini’s spacecraft narrow-angle camera, from a distance of approximately 46,000 kilometers (29,000 miles) from Enceladus. Image scale is 276 meters (906 feet) per pixel.
Below is a ‘raw’ view of Titan, and the rings.
A closeup of Titan rings, in front of Saturn's rings. Credit: NASA/JPL/Space Science Institute.
This close-up view of Titan was taken on January 15, 2011, shows the cloudy atmosphere of the moon, with the rings in the background. Cassini was about 839,213 kilometers away from Titan.
Titan and Tethys line up for a portrait of 'sibling' moons. Credit: NASA/JPL/Space Science Institute
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This image reminds me of when I was young, my parents would line me and my siblings up for pictures, oldest and tallest in the back and youngest and smallest in the front. Here, the Cassini spacecraft sees two of Saturn’s moons lined up for a family photo, showing the hazy orb of giant Titan beyond smaller Tethys.
On Tethys, the large Ithaca Chasma can be seen running roughly north-south for more than 1,000 kilometers (620 miles). Titan’s hazy atmosphere covers up the interesting surface below.
This view looks toward the Saturn-facing sides of Titan (5,150 kilometers, or 3,200 miles across) and Tethys (1,062 kilometers, or 660 miles across).
A potential cryovolcano – or ice volcano -- region on Saturn's moon Titan is shown in this image from NASA's Cassini spacecraft. This radar swath was laid on top of an image taken by Cassini's visual and infrared mapping spectrometer. Sotra Facula is located around 15 degrees south latitude, 40 degrees west longitude. Image credit: NASA/JPL-Caltech/USGS/University of Arizona
While icy cryovolcanoes on Titan have been theorized in the past, scientists didn’t have any hard evidence for them. But now, researchers from the Cassini mission have found proof that jumped out of their data in the form of 3-D mountain peaks. Using a new three-dimensional mapping technique, the team was able to create a realistic 3-D flyover of a region on Titan, above, where volcanic-like mountains appear to be lined up in a mountain range-type formation, complete with calderas and material flows. If cryovolcanoes do exist on Titan, they would potentially answer the question of why Titan has so much methane in its atmosphere.
“A combination of features makes us think we’ve found the best evidence so far for icy volcanoes on the moon Titan,” said Randy Kirk, a geophysicist with the U.S. Geological Survey and a member of the Cassini team. “Sotra Facular is a classic volcano with a crater on it and lava flows coming out of it.
Kirk presented the team’s findings at the American Geophysical Union conference in San Francisco.
Rather than erupting hot, molten rock, it is theorized that the cryovolcanoes of Titan would erupt volatiles such as water, methane, and ammonia. “A volcano is a place where material on the inside of a planetary body has gotten warm enough that it can erupt to the surface,” Kirk said. “When a body is made of ice and not rock, you get a cryovolcano.”
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Scientists have suspected cryovolcanoes might populate Titan, and the Cassini mission has collected data on several previous passes of the moon that suggest their existence. Kirk shared radar imagery from early in the Cassini spacecraft’s mission that showed Sotra Facular as bright spot on Titan’s equatorial sand sea, as seen above.
“There were thousands of places where bright ground peeks out of the dark places,” Kirk said, “and in particular we noticed a rose-type round feature, which we called The Rose, with a flows coming from it and we wondered if it was a volcano.”
Combining new data from Cassini’s radar instrument and the visual and infrared mapping spectrometer, the team was able to create the 3-D flyover movie, which shows two peaks more than 1,000 meters (3,000 feet) tall and multiple craters as deep as 1,500 meters (5,000 feet). It also shows finger-like flows. All of these are land features that indicate cryovolcanism.
“We were excited and quite happy when we saw the video,” Kirk told Universe Today at a press briefing on Tuesday. “There was a long time lapse between seeing the image of The Rose, and everybody was wondering if it was a volcano. When we finally managed to create the three dimensional from the topographic maps, I was shocked, and I made it from our own data set! I showed the video to team and they shared that reaction.”
Kirk said the flows were quite thin – thinner than anticipated at less than 100 meters (300 feet) thick — but there were more volcanoes in the same field as Sotra Facula than what the team expected.
In the video, mountains appear, with a huge pit like a volcanic calderas –“ a big bite out of the mountain,” as Kirk described it.
The topography in the video has been vertically exaggerated by a factor of 10. The false color in the initial frames show different compositions of surface material, as detected by Cassini’s visual and infrared mapping spectrometer. In this color scheme, dunes tend to look relatively brown-blue. Blue suggests the presence of some exposed ice. Scientists think the bright areas have an organic coating that hides the ice and is different and lighter than the dunes. The finger-like flows appear bright yellowish-white, like the mountain and caldera. The second set of colors shows elevation, with blue being lowest and yellow and white being the highest. Here, the dunes appear blue because they tend to occupy low areas.
This photograph shows a fissure and a row of craters in Laki, a volcanic region in the south of Iceland. Kirk said the region on Titan where potential cryovolcanoes have been found could look very similar to this landscape. Image credit: R. M. C. Lopes
Cryovolcanism could release methane from Titan’s interior, which explains Titan’s seemingly continuous supply of fresh methane in its atmosphere. Without replenishment, scientists say, Titan’s original atmospheric methane should have been exhausted long ago.
“One of mysteries on Titan is the source of methane,” said Linda Spilker, Cassini project scientist, “so cryovoclanoes offer the perfect opportunity to get methane from interior into the atmosphere of Titan.”
Kirk and his team calculated that a Sotra-sized volcanic eruption every 1,000 years would maintain the current level of methane in Titan’s atmosphere.
Jeff Kargel from the University of Arizona, who provided an independent assessment of the potential of cryovolcanoes on Titan, said that no one yet knows what the flows are made of from these volcanoes, but — providing a tantalizing visualization — said an ammonia-water cryolava with methane and carbon dioxide would make frothy, pumice-like deposits on Titan.
Kargel also added that the strongest evidence for cryovolcanoes on Titan is the topographical data that Kirk and his team have provided. “The strong evidence here is the is juxtaposition of the high and low topography in this region on Titan. There are very few tectonic activities that can produce comparable conic mountain like this.”
For more imagery from Kirk’s presentation and other presentations about the Saturn system at AGU, see this NASA webpage.
Titan's thick haze. Image: NASA/JPL/Space Science Institute.
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Saturn’s moon Titan has long been thought to be an analog of early Earth, and a recent experiment demonstrates that amino acids and nucleotide bases — which are the basic building blocks of life on Earth – could very easily be under production in Titan’s hazy atmosphere. “Our intention was to figure out what goes on in Titan’s atmosphere using high resolution mass spectrometry,” said Sarah Horst, from the University of Arizona, a member of an international team conducting the research. “We found there could be a high number of some incredibly complex molecules being created.”
Two recent exciting discoveries led the team to try and find out more about Titan’s atmosphere: first, the discovery of high energy oxygen ions flowing into Titan’s atmosphere, and second, that there are high heavy molecular ions in the atmosphere – neither of which were expected.
“When you put two discoveries together, that leads us to possibility that oxygen can get incorporated into these large molecules and in turn, that may be incorporated into life,” Horst said in press briefing at the American Astronomical Society’s Division of Planetary Sciences meeting this week.
The intense radiation that hits the top of Titan’s thick atmosphere is capable of breaking apart even very stable molecules. The international team wanted to understand what happens as these molecules are broken apart in the atmosphere.
Working with a team in France, Horst, a graduate student, and her professor Roger Yelle, filled a reaction chamber with Titan-like atmosphere, (a cold plasma consisting of nitrogen, methane and carbon monoxide), and infused radio-frequency radiation as an energy source.
“What happens is that aerosols form in levitation — they float while forming — so this probably is very representative of Titan’s atmosphere,” Horst said. “We end up with really cool looking aerosols that have very similar sizes to aerosols that are inferred in Titan’s atmosphere.”
The molecules discovered in the aerosols include the five nucleotide bases used by life on Earth (cytosine, adenine, thymine, guanine and uracil) and the two smallest amino acids, glycine and alanine.
“The experiment showed that Titan’s atmosphere is capable of producing extremely complex molecules and has the potential for producing molecules that are important for life on Earth,” Horst said, but tempered her statement by adding, “however, this doesn’t mean there is life on Titan.”
She said if there were life on Titan, mostly likely it would use molecules that life on Earth would not use, as due to lack of liquid water, life would be completely different.
“But this tells that it is possible to make very complex molecules in the outer parts of an atmosphere,” Horst said. “We don’t need liquid water, we don’t need a surface.”
This also provides another option to how life may have started on Earth. The two main theories for how life began on Earth is that it was brought here by comets or asteroids or that it formed from a primordial soup zapped to life from lightning. But it may have formed from a primordial haze high in Earth’s atmosphere.
“This helps us to understand what processes began life on Earth and what could be happening on other exoplanets in the galaxy,” Horst said.
Titan is Saturn’s largest moon, and the second largest moon in the Solar System. It’s unique in the Solar System as the only moon with an atmosphere. In fact, scientists think that Titan’s thick atmosphere – rich in hydrocarbons – is similar to the early Earth, and could give us clues about how life got started on our planet.
This graphic shows an angled view of a newly discovered “crack” in one of Saturn’s rings, known as the C ring. This view shows the 3-D quality of the puzzling crack associated with a wave-like feature that was discovered earlier by NASA’s Voyager 1 spacecraft. Image credit: NASA/JPL/Cornell
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Saturn’s rings have several gaps, most of which are caused by small moons shepherding ring debris into breaks in the rocky rings. But one gap may be caused by gravitational perturbations from Saturn’s largest moon, Titan, sending tsunami-like waves up to 3 kilometers (2 miles) high in the C ring. This causes one region of the ring to spin like a warped, uneven vinyl record on a turntable. A new model of this action explains why the gap was narrower than expected and also why is seems to disappear from time to time. “What looked like a 15-kilometer-wide gap actually was this gap with a vertical displacement of about 3 kilometers projected and seen almost edge on,” said Phillip Nicholson from Cornell University, speaking at a press briefing at the American Astronomical Society’s Division for Planetary Sciences meeting in Pasadena, California. “It’s a little like a tsunami propagating away from an earthquake fault.”
The Cassini spacecraft looks close at Saturn to frame a view encompassing the entire C ring. Image credit: NASA/JPL/SSI
The gap in the middle of the C ring has been known since Voyager 1 flew by Saturn in the 1980, and it appeared there was a 15 km-wide gap. But when Cassini arrived in 2004 and began observations, the gap was only 2 km (1.5 miles) and sometimes it wasn’t there at all.
Nicholson said only when they began to think in three dimensions were they able to solve the mystery of this gap. While most of Saturn’s rings are flat, in 2009, the angle of sunlight during Saturn’s spring equinox revealed there were lumps and bumps in the rings are as high as the Rocky Mountains.
The model Nicholson and colleagues created suggests the actual gap in the ring is about a half a kilometer wide, but part of the ring rises 3 km (2 miles) in the air up. The different angles the two spacecraft observed from made the gap look wider to Voyager than to Cassini.
“The whole pattern rotates around at the same rate as the satellite Titan orbits Saturn, once every 16 days,” said Nicholson said. Sometimes, the tsunami-like wave couldn’t be seen by the spacecraft, which accounts for how the gap seems to appear and disappear.
Nicholson said this model explains the C ring gap, “better than you have any right to expect,” but there could be three or four dynamical processes going on that explains the other gaps.
Nicholson and Cassini Deputy Project Scientist Linda Spilker said the same types of processes seen in Saturn’s rings could also explain what is seen in disks of debris around other stars, with the theory that there are gaps forming in the disks associated with the formation of planets.
New insights into the nature of Saturn’s rings are revealed in this panoramic mosaic of 15 images taken during the planet’s August 2009 equinox. Image credit: NASA/JPL/SSI
“Saturn provides a wonderful natural laboratory of how protoplanetary nebula may evolve,” said Spilker.
The Cassini scientists also noted how the Cassini mission has now moved past the “Equinox” mission and is now in another extension of the mission called the Solstice mission, which will keep the spacecraft going until 2017.
Spilker shared how as the end of the mission approaches, they might try some riskier moves, such as try flying between Saturn’s D ring or heading into Saturn’s into upper atmosphere to “study new things about planet itself, for the end of the mission.”
Clouds on Titan seen by the Cassini spacecraft on Sept. 27. 2010. Credit: NASA/JPL/Space Science Institute
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The Cassini spacecraft recently swooped by Saturn’s largest moon Titan and captured images of large patches of clouds. “These are some of the largest clouds our cameras on Cassini have yet seen on Titan!” said Carolyn Porco, Cassini imaging team lead, in an email announcing the image. “And the fact that we see them in the equatorial region is big news and may signify seasonal change is underway!”
The image was taken on September 27, 2010 and received on Earth September 28, 2010 at a distance of approximately 1,282,259 kilometers away. The spacecraft was actually at its closest approach on Sept. 24, and took a long, sustained look at the hazy moon, coming within 8,175 kilometers (5,080 miles) above the hazy moon’s surface.
Cassini’s visual and infrared mapping spectrometer also took a look at these clouds, so look for more information soon about this large region of clouds.
Cassini also used its composite infrared spectrometer instrument to take a look at Titan’s stratosphere to learn more about its vertical structure as the seasons change.
This flyby is the first in a series of high-altitude Titan flybys for Cassini over the next year and a half.
Left: T43 flyby of Titan - 12 May 2008 – VIMS images a large cloud that caps the north pole of Titan (yellowish tones). Right: T63 flyby of Titan - 12 December 2009 – VIMS still observes a huge cloud system at 40°S (yellowish tones) and the north pole of Titan free of clouds, a few months after the equinox. Credit: NASA/JPL/University of Arizona/University of Nantes/ University of Paris Diderot
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The beauty of an extended space mission is that scientists can make long term observations and find out things we’ve never known before. The Cassini spacecraft’s Visual and Infrared Mapping Spectrometer (VIMS) instrument has been monitoring clouds on Titan continuously since the spacecraft went into orbit around Saturn in 2004, and a team led by Sébastien Rodriguez (AIM laboratory – Université Paris Diderot) has used more than 2,000 VIMS images to create the first long-term study of Titan’s weather. Are they ready to make a weather forecast? They say Titan’s northern hemisphere is set for mainly fine spring weather, with polar skies clearing since the equinox in August last year.
Together with Saturn in its 30-years orbit around the Sun, Titan has seasons that last for 7 terrestrial years. The team has observed significant atmospheric changes between July 2004 (early summer in the southern hemisphere) and April 2010, the very start of northern spring. The images showed that cloud activity has recently decreased near both of Titan’s poles. These regions had been heavily overcast during the late southern summer until 2008, a few months before the equinox.
“Over the past six years, we’ve found that clouds appear clustered in three distinct latitude regions of Titan: large clouds at the north pole, patchy cloud at the south pole and a narrow belt around 40 degrees south. However, we are now seeing evidence of a seasonal circulation turnover on Titan – the clouds at the south pole completely disappeared just before the equinox and the clouds in the north are thinning out. This agrees with predictions from models and we are expecting to see cloud activity reverse from one hemisphere to another in the coming decade as southern winter approaches,” said Dr Rodriguez.
Fractional cloud coverage in Titan’s atmosphere integrated between July 2004 and April 2010. Black areas are cloud free and yellow are fully covered. Credit: NASA/JPL/University of Arizona/University of Nantes/ University of Paris Diderot
The team has used results from the Global Climate Models (GCMs) developed by Pascal Rannou (Institut Pierre Simon Laplace) to interpret the evolution of the observed cloud patterns over time. Northern polar clouds of ethane form in the Titan’s troposphere during the winter at altitudes of 30-50 km by a constant influx of ethane and aerosols from the stratosphere. In the other hemisphere, mid- and high-latitudes clouds are produced by the upwelling from the surface of air enriched in methane. Observations of the location and activity of Titan’s clouds over long periods are vital in developing a global understanding of Titan’s climate and meteorological cycle.
In Feburary 2010, the Cassini mission was extended to a few months past Saturn’s northern summer solstice in May 2017. This means that Rodriguez and his team will be able to observe the seasonal changes right the way through from mid-winter to mid-summer in the northern hemisphere.
“We have learned a lot about Titan’s climate since Cassini arrived in at Saturn but there is still a great deal to learn. With the new mission extension, we will have the opportunity to answer some of the key questions about the meteorology of this fascinating moon,” said Rodriguez.
Rodriguez presented the results at the European Planetary Science Congress 2010 in Rome.
