Category: Titan

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Recent pictures from the Cassini spacecraft of Titan’s south polar region reveal new lake features not seen in images of the same region taken a year earlier. Extensive cloud systems seen in images covering the area during past year suggest that the new lakes could be the result of a large rainstorm and that lakes on Titan owe their presence, size and distribution to the moon’s weather and changing seasons. But there must also be large underground reservoirs as well of the liquids on Titan. Those liquids aren’t water, of course, but super-cold hydrocarbons like methane.

For several years, Cassini scientists have suspected that dark areas near the north and south poles of Saturn’s largest satellite might be liquid-filled lakes. Cassini’s Imaging Science Subsystem (ISS) have now surveyed nearly all of Titan’s surface, helping to create an updated global map.

Observations have documented greater stores of liquid methane in the northern hemisphere than in the southern hemisphere. And, as the northern hemisphere moves toward summer, Cassini scientists predict large convective cloud systems will form there and precipitation greater than that inferred in the south could further fill the northern lakes with hydrocarbons.

Some of the north polar lakes are large. If full, Kraken Mare — at 400,000 square kilometers — would be almost five times the size of North America’s Lake Superior. All the north polar dark ‘lake’ areas observed by ISS total more than 510,000 square kilometers — almost 40 percent larger than Earth’s largest “lake,” the Caspian Sea.

However, evaporation from these large surface reservoirs is not great enough to replenish the methane lost from the atmosphere by rainfall and by the formation and eventual deposition on the surface of methane-derived haze particles.

“A recent study suggested that there’s not enough liquid methane on Titan’s surface to resupply the atmosphere over long geologic timescales,” said Dr. Elizabeth Turtle, Cassini imaging team associate at the Johns Hopkins University Applied Physics Lab in Laurel, Md., and lead author of a paper published today in the journal Geophysical Research Letters. “Our new map provides more coverage of Titan’s poles, but even if all of the features we see there were filled with liquid methane, there’s still not enough to sustain the atmosphere for more than 10 million years.”

Combined with previous analyses, the new observations suggest that underground methane reservoirs must exist.

Titan is the only satellite in the solar system with a thick atmosphere in which a complex organic chemistry occurs. “It’s unique,” Turtle said. “How long Titan’s atmosphere has existed or can continue to exist is still an open question.”

That question and others related to the moon’s meteorology and its seasonal cycles may be better explained by the distribution of liquids on the surface. Scientists also are investigating why liquids collect at the poles rather than low latitudes, where dunes are common instead.

“Titan’s tropics may be fairly dry because they only experience brief episodes of rainfall in the spring and fall as peak sunlight shifts between the hemispheres,” said Dr. Tony DelGenio of NASA’s Goddard Institute for Space Studies in New York, a co-author and a member of the Cassini imaging team. “It will be interesting to find out whether or not clouds and temporary lakes form near the equator in the next few years.”

Titan and the transformations on its surface brought about by the changing seasons will continue to be a major target of investigation throughout Cassini’s Equinox mission.

Source: CICLOPS

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While browsing through Cassini images of Saturn’s moon Titan, astronomer Mike Brown and some colleagues noticed a recurring pattern of clouds appearing over the frigid moon’s north pole. While a large, stable cloud has been visible in every image of Titan’s north pole obtained since its discovery, Brown noticed bright “knots or streaks” in the cloud that appeared on some images but not others, or changed in images taken hours apart. Brown thought these bright features looked similar to cumulus clouds – or even like thunderheads. But how could tropical-like thunderheads be present on a moon where surface temperatures hover around -178°C (-289°F)? Brown believes these clouds are similar to winter-time lake-effect clouds found on Earth, and are due to convection and condensation occurring in the methane and ethane lakes on Titan.

“On the Earth, lake-effect clouds occur in the winter when cold air goes over warm water (like the Great Lakes) and picks up heat and moisture and then, often, deposits it all in the form of snow on the eastern shores,” Brown told Universe Today. “On Titan the winters are so long (the north pole has been in the dark for the past ~10 years!) that the lakes retain almost no heat. But as the spring sunlight starts to hit the lakes they begin to heat up just a tiny amount and this is enough to cause little blips of evaporation and clouds.”

So, while lake-effect clouds on Earth are predominantly a winter event, on Titan, lake-effect clouds occur as spring is approaching. The clouds appear only in images taken since February 2005, as the increasing amount of sunlight has heated the liquid hydrocarbon lakes slightly and evaporation takes place. “Every time the lakes warm up just a bit, a huge dollop of evaporation occurs, which re-cools the lake, and we see a cumulus cloud pop up. The lake then has to wait for some more sunlight before it happens again,” Brown wrote in his blog.

Brown, a professor of planetary astronomy at Caltech, is known primarily for his discoveries of trans-Neptunian objects like Eris and Sedna. But he enjoys dipping his toes in the water, so to speak, in other areas as well. That includes studying the meteorology of a moon that’s over 1,200 million kilometers away. “I think it’s pretty fun,” Brown admitted.

Since spring is approaching on Titan (equinox occurs in August 2009), the cloud activity is likely to increase. Fortuitously, Cassini is scheduled to fly by Titan frequently the next few years, and Brown and his team will be keeping an eye on these lake-effect-like clouds that may have a great influence on Titan’s weather.

“When Cassini was first conceived no one even knew that clouds existed on Titan!” said Brown. “But the trick is to put a spacecraft up that has highly versatile and flexible instruments and then you’ll be able to see things even if you hadn’t anticipated them.”

Brown and his team examined the north polar clouds of Titan using data from VIMS (Visible and Infrared Mapping Spectrometer) and ISS (Imaging Science Subsystems) instruments on board the Cassini spacecraft and from adaptive optics observations from the Gemini observatory and full-disk spectroscopy of Titan from the NASA Infrared Telescope Facility (IRTF).

Titan continues to surprise planetary scientists like Brown. “I love the similarities and differences with the Earth,” he said. “Titan is the only other place that we know of that has both liquids on its surface and a thick atmosphere, so we get a chance to watch something sort of Earth-like but with some very non-terrestrial behavior.”

Source: arXiv

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NASA’s Cassini mission has detected liquid hydrocarbons on Saturn’s moon Titan, in a large, glassy lake near the moon’s south pole. Before the Cassini mission began, scientists thought Titan would have global oceans of methane, ethane and other light hydrocarbons. But after more than 40 close flybys of Titan by Cassini, data showed no global oceans exist. However hundreds of dark, lake-like features are present. Until now, it was not known whether these features were liquid or simply dark, solid material. Using Cassini’s Visual and Infrared Mapping Spectrometer (VIMS), which identifies the chemical composition of objects by the way matter reflects light, a liquid ethane lake 235 kilometers (150 miles) long was detected. This makes Titan the only body in our solar system beyond Earth known to have liquid on its surface.

“This is the first observation that really pins down that Titan has a surface lake filled with liquid,” said Bob Brown of the University of Arizona, Tucson, leader of the VIMS instrument.

Scientists had deduced through earlier observations that there was likely liquid on Titan, but this is the first incontrovertible evidence. (Emily Lakdawalla at the Planetary Society explains this excellently.)

“Detection of liquid ethane confirms a long-held idea that lakes and seas filled with methane and ethane exist on Titan,” said Larry Soderblom, a Cassini interdisciplinary scientist with the U.S. Geological Survey. “The fact we could detect the ethane spectral signatures of the lake even when it was so dimly illuminated, and at a slanted viewing path through Titan’s atmosphere, raises expectations for exciting future lake discoveries by our instrument.”

Titan’s hazy, nitrogen and methane atmosphere makes it difficult to study the moon’s surface. The liquid ethane was identified using a technique that removed the interference from the atmospheric hydrocarbons.

The VIMS instrument observed a lake, called Ontario Lacus, in Titan’s south polar region during a close Cassini flyby in December 2007. The lake is roughly 20,000 square miles (7,800 square miles) in area, slightly larger than North America’s Lake Ontario.

The ethane is in a liquid solution with methane, other hydrocarbons and nitrogen. At Titan’s surface temperatures, approximately 300 degrees Fahrenheit below zero, these substances can exist as both liquid and gas. Titan shows overwhelming evidence of evaporation, rain, and fluid-carved channels draining into what, in this case, is a liquid hydrocarbon lake.

Earth has a hydrological cycle based on water and Titan has a cycle based on methane. Scientists ruled out the presence of water ice, ammonia, ammonia hydrate and carbon dioxide in Ontario Lacus. The observations also suggest the lake is evaporating. It is ringed by a dark beach, where the black lake merges with the bright shoreline. Cassini also observed a shelf and beach being exposed as the lake evaporates.

“During the next few years, the vast array of lakes and seas on Titan’s north pole mapped with Cassini’s radar instrument will emerge from polar darkness into sunlight, giving the infrared instrument rich opportunities to watch for seasonal changes of Titan’s lakes,” Soderblom said.

More information is available at NASA’s Cassini site, JPL’s Cassini site, and the Univeristy of Arizona’s VIMS site.

Even before the Cassini spacecraft entered the Saturn system, scientists were predicting that Saturn’s moon Titan would be quite Earth-like. And every image that’s been returned of Titan’s clouds, lakes, rivers, and other landforms is proving them right. In 2005 Cassini’s imaging radar discovered a massive area of sand dunes around Titan’s equatorial region. Although these dark, windblown dunes look much like sand dunes on Earth (they’ve been compared to mountainous drifts of coffee grounds), scientists are finding that the dunes are likely made of organic molecules that are not anything at all like sand.

Titan is known to have massive amounts of hydrocarbons. New observations of Titan’s sand dunes raise the possibility that much of the sand grows from hydrocarbon particulates fallen from Titan’s thick atmosphere. Once on the ground, the particulates join together and become sand grain-size particles.

This process is called sintering – where the particles are heated enough to melt together. Scientist Jason W. Barnes of NASA’s Ames Research Center says that this sintering may produce particles that are about the same size as sand grains – between 0.18-0.25 millimeters, which are perfect for blowing in the wind and drifting into dunes.

So, this process is quite the opposite of what happens to sand on Earth, which comes from silicates, gypsum, or rock that have broken down to finer grains. But on Titan, the small hydrocarbon particulates grow together into larger grains. Barnes says the process is extremely slow, but Titan has been around long enough for this to have occurred.

Based on measurements from Cassini, the dunes are 100-200 meters high and are between 1 and 79 kilometers long. Not all over Titan’s surface has been imaged, but scientists believe up to 20 % of Titan’s surface could be covered by these hydrocarbon dunes.

Original News Source: JPL

If you’re planning a visit to Saturn’s moon Titan, make sure you bring an umbrella. You’ll need it. Not to protect you from water raining down; on frigid Titan, where temperatures dip below 180-degrees Celsius, all the water is completely frozen. No, according to scientists, there’s a steady drizzle of liquid methane coming down in the mornings.

New infrared images gathered by Hawaii’s W.M. Keck Observatory and Chile’s Very Large Telescope show that Titan’s Xanadu region experiences a steady drizzle of methane during its lengthy morning. The concept of morning is a little misleading, since Titan takes about 16 Earth days to complete one rotation. So, the “morning” drizzle actually lasts around 3 Earth days, dissipating around 10:30 a.m. local time.

Astronomers aren’t actually sure if this is a moon-wide phenomenon, or just localized around the Xanadu region of Titan. Even though large lakes and seas have been discovered around the moon’s poles, no process had been discovered that fills them with liquid… until now.

Reporting their findings in the latest issue of the online journal Science Express, researchers from UC Berkeley note that, “widespread and persistent drizzle may be the dominant mechanism for returning methane to the surface from the atmosphere and closing the methane cycle.”

The new Keck/VLT images show a widespread cloud cover of frozen methane at a height of 25 to 35 kilometres. And then there are liquid methane clouds below 20 kilometres, and finally rain falling at the lowest elevations.

The droplets of liquid methane in the rain clouds are 1,000 times larger than water vapour here on Earth, and this surprisingly makes them harder to detect. Since the droplets are larger, but still carry the same amount of moisture, they’re much more spread out, making the clouds extremely diffuse, and nearly invisible.

How much liquid is trapped in the clouds? If you squeezed them all out and spread the liquid across the surface of Titan, it would coat the entire moon to a depth of about 1.5 cm. And that’s actually the same amount as we’d get if you did the same thing with the Earth’s clouds.

Original Source: UC Berkeley News Release

Take a look at the image attached to this story. If you didn’t know any better, you’d think you were looking at a rugged coastline somewhere on Earth. Maybe some island in the Mediterranean, or Norwegian fjord. Nope, you’re looking at a completely alien world: Titan.

NASA’s Cassini spacecraft took this image on May 12, 2007 during its most recent flyby of Saturn’s largest moon. During the flyby, its radar instrument captured this image using its radar instrument. Smooth surfaces, like liquid are seen as black, while the textured regions are land.

While other bodies of liquid such as lakes have been seen on Titan before, nothing has had these kinds of features: channels, islands, bays, and other terrain you’d see on Earth. But instead of water, this liquid is probably a mixture of ethane and methane. Since there are no brighter regions in the liquid regions of the image, scientists are assuming the ocean exceeds tens of metres deep.

The image is about 160 kilometers (100 miles) by 270 kilometers (170 miles) across.

Original Source: NASA/JPL/SSI/ESA News Release