On the left, Saturn's moon Enceladus is backlit by the sun, showing the fountain-like sources of the fine spray of material that towers over the south polar region. On the right, is a composite image of Titan. Image credit: NASA/JPL/SSI and NASA/JPL/University of Arizona
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It’s a space navigator’s dream! The Cassini spacecraft will perform close flybys of two of Saturn’s most enigmatic moons all within less than 48 hours, and with no maneuvers in between. Enceladus and Titan are aligned just right so that Cassini can catch glimpses of these two contrasting moons – one a geyser world and the other an analog to early Earth.
Cassini will make its closest approach to Enceladus late at night on May 17 Pacific time, which is in the early hours of May 18 UTC. The spacecraft will pass within about 435 kilometers (270 miles) of the moon’s surface.
The main scientific goal at Enceladus will be to watch the sun play peekaboo behind the water-rich plume emanating from the moon’s south polar region. Scientists using the ultraviolet imaging spectrograph will be able to use the flickering light to measure whether there is molecular nitrogen in the plume. Ammonia has already been detected in the plume and scientists know heat can decompose ammonia into nitrogen molecules. Determining the amount of molecular nitrogen in the plume will give scientists clues about thermal processing in the moon’s interior.
Then on to Titan: the closest approach will take place in the late evening May 19 Pacific time, which is in the early hours of May 20 UTC. The spacecraft will fly to within 1,400 kilometers (750 miles) of the surface.
Cassini will primarily be doing radio science during this pass to detect the subtle variations in the gravitational tug on the spacecraft by Titan, which is 25 percent larger in volume than the planet Mercury. Analyzing the data will help scientists learn whether Titan has a liquid ocean under its surface and get a better picture of its internal structure. The composite infrared spectrometer will also get its southernmost pass for thermal data to fill out its temperature map of the smoggy moon.
Cassini has made four previous double flybys and one more is planned in the years ahead.
For more information on the Enceladus flyby, dubbed “E10,” see this link.
For more information on the Titan flyby, dubbed “T68,” see this link.
Artist concept of Methane-Ethane lakes on Titan (Credit: Copyright 2008 Karl Kofoed). Click for larger version.
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Could there be life on Titan? If so, one astrobiologist says humans probably couldn’t be in the same room with a Titanian and live to tell about it. “Hollywood would have problems with these aliens” said Dr. William Bains. “Beam one onto the Starship Enterprise and it would boil and then burst into flames, and the fumes would kill everyone in range. Even a tiny whiff of its breath would smell unbelievably horrible. But I think it is all the more interesting for that reason. Wouldn’t it be sad if the most alien things we found in the galaxy were just like us, but blue and with tails?”
While giving an obvious nod to the recent movie “Avatar,” Bains’ research provides insight to the difficulties we might encounter – beyond cultural – if we ever meet up with alien life. There could be unintended harmful consequences for one species, or both.
Bains is working to find out just how extreme the chemistry of life can be. Life on Titan, Saturn’s largest moon, represents one of the more bizarre scenarios being studied. While images sent back by the Cassini/Huygens mission might make Titan look Earth-like and maybe even inviting, it has a thick atmosphere of frozen, orange smog. At ten times our distance from the Sun, it is a frigid place, with a surface temperature of -180 degrees Celsius. Water is permanently frozen into ice and the only liquid available is liquid methane and ethane.
So instead of water based-life (like us), life on Titan would likely be based on methane.
“Life needs a liquid; even the driest desert plant on Earth needs water for its metabolism to work. So, if life were to exist on Titan, it must have blood based on liquid methane, not water. That means its whole chemistry is radically different. The molecules must be made of a wider variety of elements than we use, but put together in smaller molecules. It would also be much more chemically reactive,” said Bains.
Additionally, Bains said a metabolism running in liquid methane would have to be built of smaller molecules than terrestrial biochemistry.
“Terrestrial life uses about 700 molecules, but to find the right 700 there is reason to suppose that you need to be able to make 10 million or more,” Bains said. “The issue is not how many molecules you can make, but whether you can make the collection you need to assemble a metabolism.”
Bains said doing such assembling is like trying to find bits of wood in a lumber-yard to make a table.
“In theory you only need 5,” he said. “But you may have a lumber-yard full of offcuts and still not find exactly the right five that fit together. So you need the potential to make many more molecules than you actually need. Thus the 6-atom chemicals on Titan would have to include much more diverse bond types and probably more diverse elements, including sulphur and phosphorus in much more diverse and (to us) unstable forms, and other elements such as silicon.”
Energy is another factor that would affect the type of life that could evolve on Titan. With Sunlight a tenth of a percent as intense on Titan’s surface as on the surface of Earth, energy is likely to be in short supply.
“Rapid movement or growth needs a lot of energy, so slow-growing, lichen-like organisms are possible in theory, but velociraptors are pretty much ruled out,” said Bains.
Whatever life may be on Titan, at least we know there won’t be a Jurassic Park.
Bains, whose research is carried out through Rufus Scientific in Cambridge, UK, and MIT in the USA, is presenting his research at the National Astronomy Meeting in Glasgow, Scotland on April 13, 2010.
The first interplanetary nautical craft may be a boat to explore the methane seas of Titan. A proposed mission to Titan would explore some of its largest seas, including Ligeia Mare (pictured) or the Kraken Mare, both of which are in the northern hemisphere of the foggy moon of Saturn. The concept has been studied for over two years by scientific team led by Ellen Stofan of Proxemy Research, Inc. in Washington DC, and has recently been submitted to NASA.
The concept is under consideration by NASA to be one of the Discovery Class missions – low-cost, high-return missions, which include the MESSENGER and Kepler missions. If chosen, the Titan Mare Explorer (TiME), could launch as early as January of 2015, and would make port at Titan in June of 2023. The total proposed cost of TiME is currently estimated at $425 million. Stofan described the proposal at this year’s American Geophysical Union meeting in San Fransisco, CA.
Lakes, seas, and rivers were discovered on Titan by the Cassini spacecraft in 2005. Since then, the weather and climate patterns of the moon have been scrutinized by scientists, leading to the discovery of both fog and rain.
Of course, the proposed boat wouldn’t be the first craft to land on Titan – that distinction is held by the Huygens probe, which as part of the Cassini mission landed on Titan on January 14th, 2005 and for three hours took images and scientific data which it sent back to Earth. Huygens touched down on dry land, though it was designed to operate on either land or ocean.
Proposed instruments for the boat include a mass spectrometer, sonar, cameras and meteorology instruments. TiME would investigate the chemical composition of the seas of Titan, as well as monitor the cycle of ethane and methane on the moon (called the “methane-ologic” cycle), a process that scientists are just beginning to understand. The sonar would be used just like it is on submarines and boats here on Earth – to map the depth of the seas, as well as get an accurate image of the sea bottom.
Since the cloudy and foggy surface of Titan sees little sunlight, the boat is proposed to be powered by an Advanced Stirling Radioisotope Generator. These types of engines, called Stirling engines after the inventor, Robert Stirling, use a radioactive source such as plutonium to heat a gas in one chamber, and as it flows to a cooler chamber the flow is turned into mechanical energy with a very high rate of efficiency.
If the boat is seaworthy, it may set a precedent to give us Earthlubbers a chance at understanding the only other body in our Solar System with lakes and seas on its surface (though Europa and Enceladus are thought to have watery oceans under their crusts). By comparing the methane-ologic cycle on Titan with the Earth’s hydrologic cycle, scientists could gain a more intricate knowledge of the large-scale impact of these cycles.
Source: Physorg, Ellen Stofan’s presentation (available here in PDF)
This image shows the first flash of sunlight reflected off a lake on Saturn’s moon Titan. Credit: NASA/JPL
Dear friend,
Ah, yes. Another gorgeous day here in the northern lake district. It warmed up to about 94 K (-179 °C, or -290 °F) and we sat and enjoyed the sunshine gleaming off the liquid lakes here on Titan. Wish you were here!
Liquid lakes? Gleaming sunshine? Titan?
Yes, it’s all true. The Cassini Spacecraft has captured the first flash of sunlight reflected off a lake on Saturn’s moon Titan, confirming the presence of liquid on the part of the moon dotted with many large, lake-shaped basins.
Cassini scientists had been looking for the glint, also known as a specular reflection, since the spacecraft began orbiting Saturn in 2004. But Titan’s northern hemisphere, which has more lakes than the southern hemisphere, has been veiled in winter darkness. The sun only began to directly illuminate the northern lakes recently as it approached the equinox of August 2008, the start of spring in the northern hemisphere. Titan’s hazy atmosphere also blocked out reflections of sunlight in most wavelengths. This serendipitous image was captured on July 8, 2009, using Cassini’s visual and infrared mapping spectrometer.
This image is being presented at the fall meeting of the American Geophysical Union in San Francisco.
“This one image communicates so much about Titan — thick atmosphere, surface lakes and an otherworldliness,” said Bob Pappalardo, Cassini project scientist, based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “It’s an unsettling combination of strangeness yet similarity to Earth. This picture is one of Cassini’s iconic images.”
Titan, Saturn’s largest moon, has captivated scientists because of its many similarities to Earth. Scientists have theorized for 20 years that Titan’s cold surface hosts seas or lakes of liquid hydrocarbons, making it the only other planetary body besides Earth believed to harbor liquid on its surface. While data from Cassini have not indicated any vast seas, they have revealed large lakes near Titan’s north and south poles.
In 2008, Cassini scientists using infrared data confirmed the presence of liquid in Ontario Lacus, the largest lake in Titan’s southern hemisphere. But they were still looking for the smoking gun to confirm liquid in the northern hemisphere, where lakes are also larger.
Katrin Stephan, of the German Aerospace Center (DLR) in Berlin, an associate member of the Cassini visual and infrared mapping spectrometer team, was processing the initial image and was the first to see the glint on July 10th.
“I was instantly excited because the glint reminded me of an image of our own planet taken from orbit around Earth, showing a reflection of sunlight on an ocean,” Stephan said. “But we also had to do more work to make sure the glint we were seeing wasn’t lightning or an erupting volcano.”
Team members at the University of Arizona, Tucson, processed the image further, and scientists were able to compare the new image to radar and near-infrared-light images acquired from 2006 to 2008.
They were able to correlate the reflection to the southern shoreline of a lake called Kraken Mare. The sprawling Kraken Mare covers about 400,000 square kilometers (150,000 square miles), an area larger than the Caspian Sea, the largest lake on Earth. It is located around 71 degrees north latitude and 337 degrees west latitude.
The finding shows that the shoreline of Kraken Mare has been stable over the last three years and that Titan has an ongoing hydrological cycle that brings liquids to the surface, said Ralf Jaumann, a visual and infrared mapping spectrometer team member who leads the scientists at the DLR who work on Cassini. Of course, in this case, the liquid in the hydrological cycle is methane rather than water, as it is on Earth.
“These results remind us how unique Titan is in the solar system,” Jaumann said. “But they also show us that liquid has a universal power to shape geological surfaces in the same way, no matter what the liquid is.”
This mosaic of Cassini, SAR, ISS, and VIS images data shows that there are many more lakes in the northern regions of Titan than in the south. The eccentric orbit of Saturn is thought to have caused this imbalance. Image Credit: NASA/JPL/Caltech/University of Arizona/Cassini Imaging Team
If you’ve wanted to take a swim in a lake on Titan, don’t: they’re not lakes like we have here on Earth, composed of methane and ethane instead of water. If you have somehow evolved lungs to breathe and swim in these chemicals, you should take your beach vacation in the northern hemisphere of Titan, where you’ll find many more lakes. Data taken by the Cassini mission has shown that there are more of these methane lakes concentrated in the northern hemisphere of Saturn’s moon than in the southern hemisphere. A recent analysis of the Cassini findings by a team at Caltech has shown that the cause of this asymmetry of lakes is due to the orbit of Saturn.
Because of the eccentricity of Saturn’s orbit around the Sun, there is a constant transfer of methane in Titan’s atmosphere from the south to the north. This effect is called astronomical climate forcing, or the Milankovitch cycle, and is thought to be the cause of ice ages here on Earth. We wrote about the Milankovitch cycles and their influence on climate change just earlier today.
Scientists originally thought that the northern hemisphere was somehow differently structured than the south. Imaging data from Cassini showed that ethane and methane lakes cover 20 times more area in the northern hemisphere than lakes in the south. There also are more half-filled and dried-up lake beds in the north. For example, if the composition of the surface of Titan somehow allowed for more methane and ethane to permeate the ground more in the north, this could have explained the difference. But further data from Cassini has confirmed that there is no great difference in topography between the two hemispheres of Titan.
The seasonal differences on Titan only partially explain the asymmetry of lake formation. One year on Titan is 29.5 Earth years, so about every 15 years the seasons of Titan reverse. In other words, the winter and summer seasons could have caused the evaporation and transfer of gas to the north, where it is cooled and is currently in the form of lakes until the seasons change again.
A team led by Oded Aharonson, associate professor of planetary science at Caltech found that there was much more to the story, though. The seasonal effect could only account for changes in lake depth for each hemisphere to vary by about one meter. Titan’s lakes are hundreds of meters deep on average, and this process is too slow to explain the depth changes we see today. It became apparent that the seasonal differences were only partly contributing to this difference.
“On Titan, there are long-term climate cycles in the global movement of methane that make lakes and carve lake basins. In both cases we find a record of the process embedded in the geology,” Aharonson said in a press release.
The Milankovitch cycle on Titan is likely the cause of the lake imbalance. Summers in the north are long and relatively mild, while those in the south are shorter, but warmer. Over thousands of years, this leads to a net movement of gas towards the north, which then condenses and stays there in liquid form. During southern summer Titan is close to the sun, and during northern summer it is approximately 12% further from the Sun.
Their results appear in the advance online version of Nature Geoscience for November 29th. Animations detailing the transfer are available on Oded Aharonson’s home page.
If Cassini would have been sent to Titan 32,000 years ago, the picture would have been reversed: the south pole would have many more lakes than the north. Conversely, any Titanian deep-lake divers in a few thousand years will fare much better in the lakes of the south.
Stereographic projection of Synthetic Aperture Radar (SAR) imagery of Titan’s south polar region obtained between Sep. 2005 and July 2009. The Cassini radar has observed 60% of this area and 9% has repeat coverage. Areas where changes have been detected are outlined in red. Credit: Alex Hayes and Jonathan Lunine
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New images of Titan’s surface from the Cassini spacecraft show changes which are evidence of seasonal change. Objects identified earlier as liquid hydrocarbon lakes are shrinking and disappearing over the course of one to several Earth years. Scientists say seasonal temperature variations causing evaporation is the most likely cause for the changes observed. Cassini’s Synthetic Aperture Radar (SAR) repeatedly peered through Titan’s thick atmosphere, and data show that the lakes exhibit more than an order of magnitude increase in radar return and have disappearing borders between observations, suggesting surface change. These changes cannot be explained without invoking temporal variability, scientists reported at the American Astronomical Society’s Division for Planetary Sciences meeting now under way in Fajardo, Puerto Rico.
Alex Hayes, of the California Institute of Technology, and Dr. Jonathan Lunine, of the University of Rome Tor Vergata shared images of several regions on Titan’s south pole. Ontario Lacus is the largest and best characterized lake on Titan. Between July 2004 and July 2009, the shorelines of Ontario Lacus have receded, consistent with liquid evaporation and/or infiltration. In June and July 2009, the Cassini radar acquired its first high-resolution SAR images of the lake. Together with closest approach altimetry acquired in December 2008, these observations provide a unique opportunity to study Ontario. Areas where the Cassini radar has observed transient surface liquid in Titan’s south polar region. The top two images are located near (60S, 210W) and were obtained in December 2007 and May 2009. Empty lake features are outlined in red and filled lakes, observed in the 2007 image, are outlined in cyan. The lake features disappear between observations. The bottom row consists of images near (69S, 90W) obtained in Oct. 2007 and Dec. 2008. Empty lake features observed in Dec. 2008 are outlined in red. The empty lake features in the bottom-left section of the image are dark in Oct. 2007, consistent with liquid-filled lakes. In the Dec. 2008 image the brightness of these features are indistinguishable from the empty lakes in the upper-right section of the image (which are bright in both observations), suggesting surface change.
Evaporation is the most likely scenario for observed changes on Titan’s surface. Alternative explanations include freezing, cryovolcanism, and subsurface infiltration. Freezing is unlikely due to thermodynamic reasons during the summer season in Titan’s south pole, and there are no clearly observable cryovolcanic features in the study areas. However, liquids evaporating and becoming part of a static hydrologic system is inconsistent with the observations. But, the scientists said, infiltration into a dynamic hydrologic system with a regionally varying methane/ethane table is possible.
“If evaporation is responsible, model results suggest rates are about 1m/yr, similar to current GCM estimates of methane evaporation rates for the latitudes and season in question,” Hayes and Lunine wrote in their press release. “An analysis of the receding shorelines observed in Ontario Lacus also yield evaporation rates of about 1 m/yr and support the results of the two- layer model for the smaller lakes. These observations constrain volatile fluxes and hence, the evolution of Titan’s hydrologic system.”
Crucial building blocks in the organic haze layers of Titan and possibly of early Earth come from chemical reactions. Image credits courtesy of NASA-JPL, Dr. Xibin Gu, and Reaction Dynamics Group, University of Hawaii.
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Titan appears to be more like Earth all the time, and a new understanding of Titan’s hazy atmosphere could provide clues to the evolution of Earth’s early atmospheric environment and the development of life on our home planet. Researchers have discovered a series of chemical reactions on Saturn’s largest moon that may shield the moon’s surface from ultraviolet radiation, similar to how Earth’s ozone layer works. The reactions may also be responsible for forming the large organic molecules that compose the moon’s thick and hazy orange atmosphere.
Scientists have long understood that high in Titan’s atmosphere, sunlight breaks apart methane into carbon and hydrogen. These elements react with nitrogen and other ingredients to form a thick haze of complex hydrocarbons which completely enshrouds the moon.
But recently, the role of polyynes in the chemical evolution of Titan’s atmosphere has been vigorously researched and debated. Polyynes are a group of organic compounds with alternating single and triple bonds, such as diacetylene (HCCCCH) and triacetylene (HCCCCCCH). These polyynes are thought to serve as an UV radiation shield in planetary environments, and could act as prebiotic ozone. This would be important for any life attempting to form on Titan.
“Even if you form biologically important molecules (via other reactions) and there is no ozone or ozone like-layer, these molecules will not always survive the harsh radiation environment,” said Ralf Kaiser, lead scientist of the study.
However, the underlying chemical processes that initiate the formation and control the growth of polyynes have not been understood.
Kaiser and his colleagues studied the formation of triacetylene and larger organic molecules in the lab and in computer simulations. They found that triacetylene can be formed by collisions between two small molecules in a reaction that can be easily initiated under the cold conditions found in Titan’s atmosphere.
The authors suggest that triacetylene, an organic molecule that could act as a shield for ultraviolet radiation, may serve as the building block for creating complex molecules in Titan’s atmosphere.
“The present experiments are conducted with molecules containing carbon and hydrogen atoms only,” Kaiser told Universe Today. “To investigate the formation of astrobiologically important molecules on Titan, we have to ‘add’ oxygen and nitrogen, too.” Kaiser said they plan to do those type of experiments later this year.
The team said they hope their combined experimental,theoretical, and modeling study will act as a template, and trigger much needed, successive investigation of the chemistry of surrounding Titan so that a more complete picture of the processes involved in the chemical processing of moon’s atmosphere will emerge.
Lead image caption: Crucial building blocks in the organic haze layers of Titan and possibly of early Earth come from chemical reactions. Image credits courtesy of NASA-JPL, Dr. Xibin Gu, and Reaction Dynamics Group, University of Hawaii
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Titan is the only place in the solar system other than the earth that appears to have large quantities of liquid sitting on the surface. Granted, conditions on Titan are quite different than on Earth. For one thing, it’s a lot colder on Titan and the liquids there are various types of hydrocarbons. “Methane is to Titan what water is to the earth,” says astronomer Mike Brown (yes, that guy, of Pluto, Eris and Makemake fame.) But now Brown and his colleagues have discovered another similarity. Titan has fog. “All of those bright sparkly reddish white patches (shown in the image here) are fog banks hanging out at the surface in Titan’s late southern summer,” Brown wrote in his blog.
Wow.
But how does this happen? Fog only usually appears when 1.) there is liquid in the atmosphere (i.e., that means it must be “humid” on Titan) and 2.) the air temperature cools drastically. But Titan’s atmosphere is extremely thick, so it cools slowly. Plus the atmosphere is already really cold and making it colder would be difficult.
“If you were to turn the sun totally off,” said Brown, “Titan’s atmosphere would still take something like 100 years to cool down. And even the coldest parts of the surface are much too warm to ever cause fog to condense.”
So what is going on there?
To get the humidity in Titan’s atmosphere, Brown said the liquid methane must be evaporating.
“Evaporating methane means it must have rained,” he wrote. “Rain means streams and pools and erosion and geology. Fog means that Titan has a currently active methane hydrological cycle doing who knows what on Titan.”
Plus, the only one way to make the fog stick around on the ground for any amount of time is have both humidity and cool air. And the only way to cool the air on Titan is have it in contact with something cold: like a pool of evaporating liquid methane.
Brown said the fog doesn’t appear to be around the just the dark areas near the south pole that likely are hydrocarbon lakes. “It looks like it might be more or less everywhere at the south pole. My guess is that the southern summer polar rainy season that we have witnessed over the past few years has deposited small pools of liquid methane all over the pole. It’s slowly evaporating back into the atmosphere where it will eventually drift to the northern pole where, I think, we can expect another stormy summer season. Stay tuned. Northern summer solstice is in 2016.”
And here comes the fun part (as if fog on Titan wasn’t fun enough!) Brown is looking for a little citizen science help. You can read the paper on this by Brown and his colleagues here. Most peer review is done by one person, and brown would like a few more eyes to see this paper to look for any flaws, and to see if their arguments make sense and are convincing.
Brown says: “I thought I would try an experiment of my own here. It goes like this: feel free to provide a review of my paper! I know this is not for everyone. Send it directly to me or comment here (at his blog). I will take serious comments as seriously as those of the official reviewer and will incorporate changes into the final version of the paper before it is published.
CREDIT: Gemini Observatory/AURA/Henry Roe, Lowell Observatory/Emily Schaller, Insitute for Astronomy, University of Hawai‘i
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Titan is just fun. Seems like every other week, another fascinating tidbit emerges about how interesting Saturn’s famous moon really is — and how compellingly similar to Earth.
A United States team of astronomers is releasing this image today in Nature. It’s an adaptive optics peek at a storm over the wild object’s parched, dry desert.
The new research, to be published in the August 13 issue of the journal, announces the discovery of significant cloud formation (about three million square kilometers, or 1.16 million square miles) within the moon’s tropical zone near its equator. Prior to this event (in April 2008) it was not known whether significant cloud formation was possible in Titan’s tropical regions. This activity in Titan’s tropics and mid-latitudes also seems to have triggered subsequent cloud development at the moon’s south pole where it was considered improbable due to the Sun’s seasonal angle relative to Titan.
The evidence comes from astronomers using the Gemini North telescope and NASA’s Infrared Telescope Facility (IRTF), both on Hawaii’s Mauna Kea.
“We obtain frequent observations with IRTF giving us a ‘weather report’ of sorts for Titan. When the IRTF observations indicate that cloud activity has increased, we are able to trigger the next night on the Gemini telescope to determine where on Titan the clouds are located,” said team member Emily Schaller, who was at the University of Hawai‘i Institute for Astronomy when this work was done.
Saturn and Titan (six o'clock). CREDIT: Gemini Observatory/AURA/Henry Roe, Lowell Observatory/Emily Schaller, Insitute for Astronomy, University of Hawai‘i
Titan, the solar system’s second largest moon, has received considerable attention by scientists since NASA’s Cassini mission deployed the Huygens probe that descended through the moon’s atmosphere in January 2005. During its descent, the probe’s cameras revealed small-scale channels and what appear to be stream beds in the equatorial regions that seemed to contradict atmospheric models predicting extremely dry desert-like conditions near the equator. Until now these erosional (fluvial) features have been explained by the possibility of liquid methane seeping out of the ground.
“In April 2008 we observed what was a global event that shows how storm activity in one region can trigger clouds, and probably rainfall, over arid regions, such as the tropics where Huygens landed,” said team member Henry Roe, an astronomer at Lowell Observatory. “Of course these rain showers are not liquid water like here on Earth, but are instead made of liquid methane. Just like the streambeds and channels that are carved by liquid water on Earth, we see features on Titan that have been created by flowing liquid methane.”
Unlike the Earth, on Titan, where the temperature is hundreds of degrees below freezing, methane (or natural gas) is a liquid and it the dominant driver of the moon’s weather and surface erosion. Any water on Titan is frozen on or below the moon’s surface and resemble rocks or boulders on Titan’s surface.
Mid-latitude and polar cloud formations have been bserved for many years (by this team and others) but the combination of extensive monitoring at the IRTF with rapid follow-up using Gemini allowed the team to capture the process as it unfolded near the equator. The team monitored Titan on 138 nights over 2.2 years and during that time cloud cover was well under one percent. Then, mid-April of 2008, just after team member and Ph.D. candidate Schaller had handed in her doctoral dissertation focusing on Titan’s minimal cloud cover she noticed the dramatic increase in cloud cover.
During this three-week episode clouds forming at about 30 degrees south latitude were observed, followed several days later by clouds closer to the equator and at the moon’s south pole. The apparent connection between the cloud formations leads to the possibility that cloud formation in one area of the moon can instigate clouds in other areas by a process known as atmospheric teleconnections. This same phenomena occurs in the Earth’s atmosphere and is caused by what are called planetary Rossby waves which are well understood.
The high-resolution Gemini images of Titan were all obtained with adaptive optics technology which uses a deformable mirror to remove distortions to light caused by the Earth’s atmosphere and produce images showing remarkable detail in the tiny disk of the moon.
“Without this technology this discovery would be impossible from the surface of the Earth,” said Schaller. Currently the Cassini spacecraft is orbiting Saturn but only flies by Titan once every 6 weeks or so. This makes continuous ground-based monitoring important for studying features like these with shorter periods on the order of 3-weeks like this storm.
Further detail about the lead image: Gemini North adaptive optics image of Titan showing storm feature (bright area). Titan is about 0.8 arcsecond across in this 2.12 micron near-infrared image obtained on April 14, 2008 (UTC). CREDIT: Gemini Observatory/AURA/Henry Roe, Lowell Observatory/Emily Schaller, Insitute for Astronomy, University of Hawai‘i
An artist's imagination of hydrocarbon pools, icy and rocky terrain on the surface of Saturn's largest moon Titan. Image credit: Steven Hobbs (Brisbane, Queensland, Australia)
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It’s more than a billion kilometers (759 million miles) away, but the more astronomers learn about Titan, the more it looks like Earth.
That’s the theme of two talks happening this week at the International Astronomical Union meeting in Rio de Janeiro, Brazil. Two NASA researchers, Rosaly Lopes and Robert M. Nelson of the Jet Propulsion Laboratory in Pasadena, California, are reporting that weather and geology have very similar actions on Earth and Titan — even though Saturn’s moon is, on average, 100 degrees C (212 degrees F) colder than Antarctica (and certainly much more frigid than either California or Brazil; lucky astronomers).
The researchers are also reporting a tantalizing clue in the search for life: Titan hosts chemistry much like pre-biotic conditions on Earth.
Wind, rain, volcanoes, tectonics and other Earth-like processes all sculpt features on Titan’s complex and varied surface — except, according to additional research being presented at the meeting, scientists think the “cryovolcanoes” on Titan eject cold slurries of water-ice and ammonia instead of scorching hot magma.
“It is really surprising how closely Titan’s surface resembles Earth’s,” Lopes said. “In fact, Titan looks more like the Earth than any other body in the Solar System, despite the huge differences in temperature and other environmental conditions.”
The joint NASA/ESA/ASI Cassini-Huygens mission has revealed details of Titan’s geologically young surface, showing few impact craters, and featuring mountain chains, dunes and even “lakes.” The RADAR instrument on the Cassini orbiter has now allowed scientists to image a third of Titan’s surface using radar beams that pierce the giant moon’s thick, smoggy atmosphere. There is still much terrain to cover, as the aptly named Titan is one of the biggest moons in the Solar System, larger than the planet Mercury and approaching Mars in size.
New Cassini mosaic showing a dried-out lake at Titan's south pole.
Titan has long fascinated astronomers as the only moon known to possess a thick atmosphere, and as the only celestial body other than Earth to have stable pools of liquid on its surface. The many lakes that pepper the northern polar latitudes, with a scattering appearing in the south as well, are thought to be filled with liquid hydrocarbons, such as methane and ethane.
On Titan, methane takes water’s place in the hydrological cycle of evaporation and precipitation (rain or snow) and can appear as a gas, a liquid and a solid. Methane rain cuts channels and forms lakes on the surface and causes erosion, helping to erase the meteorite impact craters that pockmark most other rocky worlds, such as our own Moon and the planet Mercury.
Another Cassini instrument called the Visual and Infrared Mapping Spectrometer (VIMS) had previously detected an area, called Hotei Regio, with a varying infrared signature, suggesting the temporary presence of ammonia frosts that subsequently dissipated or were covered over. Although the ammonia does not stay exposed for long, models show that it exists in Titan’s interior, indicating that a process is at work delivering ammonia to the surface. RADAR imaging has indeed found structures that resemble terrestrial volcanoes near the site of suspected ammonia deposition.
Nelson said new infrared images of the region, also presented at the IAU, “provide further evidence suggesting that cryovolcanism has deposited ammonia onto Titan’s surface. It has not escaped our attention that ammonia, in association with methane and nitrogen, the principal species of Titan’s atmosphere, closely replicates the environment at the time that life first emerged on Earth. One exciting question is whether Titan’s chemical processes today support a prebiotic chemistry similar to that under which life evolved on Earth?”
Many Titan researchers hope to observe Titan with Cassini for long enough to follow a change in seasons. Lopes thinks that the hydrocarbons there likely evaporated because this hemisphere is experiencing summer. When the seasons change in several years and summer returns to the northern latitudes, the lakes so common there may evaporate and end up pooling in the south.
Lead image caption: Artist’s impression of hydrocarbon pools, icy and rocky terrain on the surface of Saturn’s largest moon Titan. Image credit: Steven Hobbs (Brisbane, Queensland, Australia)
