Lake-Effect Clouds Discovered on Titan


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

Electrical Activity on Titan Confirmed: The Spark for Life?

Titan not only has an atmosphere it has hydrocarbon lakes, oceans, sand dunes and now research has just been published proving Saturn’s moon is sparkling with electrical activity. Scientists are in general agreement that organic molecules, the precursors to life on Earth, are a consequence of lightning in the atmosphere. Now, using data from the Huygens probe that descended through Titan’s atmosphere in 2005 and continued transmitting for 90 minutes after touchdown, Spanish scientists have “unequivocally” proven that Titan has electrical storms too. The presence of electrical activity in the atmosphere is causing much excitement as this could mean that organic compounds may be found in abundance on the Titan surface.

The fruits from the Cassini-Huygens mission are coming thick and fast. Only yesterday, Nancy reviewed the discovery of liquid hydrocarbon lakes by Cassini’s Visual and Infrared Mapping Spectrometer (VIMS). Although possible lakes have been theorized, it is only now that there is observational proof of the existence of such features. Now, three years after the Huygens probe dropped through Titan’s atmosphere, scientists have made another crucial discovery: Titan experiences electrical activity in its atmosphere. Now Titan has all the necessary components for life; it has an atmosphere with electrical activity, increasing the opportunity for prebiotic organic compounds to form, thus increasing the possibility for life to evolve.

According to Juan Antonio Morente from the University of Granada, Titan is already considered a “unique world in the solar system” since the early 20th Century when Spanish astronomer José Comas y Solá made the discovery that the Saturn moon had an atmosphere. This is what makes Titan special, it has a thick atmosphere, something that is not observed on any other natural satellite in the Solar System.

On this moon clouds with convective movements are formed and, therefore, static electrical fields and stormy conditions can be produced. This also considerably increases the possibility of organic and prebiotic molecules being formed, according to the theory of the Russian biochemist Alexander I. Oparín and the experiment of Stanley L. Miller [who managed to synthesise organic compounds from inorganic compounds through electrical discharges] That is why Titan has been one of the main objectives of the Cassini-Huygens joint mission of NASA and the European Space Agency” – Juan Antonio Morente.

Morente and his team analysed data from Huygens’ Mutual Impedance Probe (MIP) that measured the atmospheric electrical field. The MIP instrument was primarily used to measure the atmosphere’s electrical conductivity but it also acted as a dipolar antenna, detecting the natural electric field. The MIP was therefore able to detect a set of spectral peaks of extremely low frequency (ELF) radio signals (known as “Schumann resonances”). These ELF peaks are formed between the moon’s ionosphere and a huge resonant cavity in which electromagnetic fields are confined.

The detection of these signals have led the Spanish researchers to state that it is “irrefutable” evidence of electrical activity on Titan, not dissimilar to static charge that builds up in the terrestrial atmosphere, leading to electrical storms.

Source: Scientific Blogging

Liquid Lake on Titan Confirmed


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.”

The dark area near the top is Ontario Lacus.  Credit: NASA / JPL / Space Science Institute
The dark area near the top is Ontario Lacus. Credit: NASA / JPL / Space Science Institute

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.

Titan’s Hydrocarbon ‘Sand’ Dunes

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

Underground Oceans Discovered on Titan


With each flyby, NASA’s Cassini spacecraft has been building up the case that there are lakes and seas of liquid hydrocarbons on the surface of Saturn’s moon Titan. But now we get the stunning news that the planet might have vast oceans of water and ammonia underneath its surface as well.

Over the course of 19 separate Cassini Titan flybys, members on the mission science team carefully established the position of 50 unique landmarks on the surface of the moon. After each flyby, they located the landmarks again, and marked their positions.

During nearly 2 years of flybys, from October 2005 to May 2007, surface features had moved from their original positions by up to 30 km (19 miles). The only way the surface could be shifting like this is if the moon’s icy crust is floating atop an internal ocean.

“We believe that about 62 miles beneath the ice and organic-rich surface is an internal ocean of liquid water mixed with ammonia,” said Bryan Stiles of NASA’s Jet Propulsion Laboratory (JPL) in, Pasadena, Calif.

Since Titan has an incredibly thick atmosphere, 1.5 times more dense than the Earth, it’s possible that powerful winds are rocking the moon back and forth around its axis. It might be speeding the rotation up at one point in the year, and then slowing it back down again. But this would only be possible if there’s an ocean underneath the surface that the entire crust floats on top of.

“The combination of an organic-rich environment and liquid water is very appealing to astrobiologists,” said Ralph Lorenz, lead author of the paper and Cassini radar scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Md. “Further study of Titan’s rotation will let us understand the watery interior better, and because the spin of the crust and the winds in the atmosphere are linked, we might see seasonal variation in the spin in the next few years.”

Researchers will get another chance to test their theories shortly. Cassini is due to make another Titan flyby on March 25th, at an altitude of only 1,000 km (620 miles).

The research will be published in the March 21st issue of the journal Science.

Original Source: NASA News Release

Titan has “Hundreds of Times More” Liquid Hydrocarbons Than Earth


According to new Cassini data, Saturns largest moon, Titan, has “hundreds” times more liquid hydrocarbons than all the liquid fossil fuel deposits on Earth. This is impressive as Titan’s 5150 km diameter is only about 50% larger than Earth’s Moon and only a little larger than the planet Mercury. Titan’s hydrocarbons cycle into the atmosphere, fall as rain and collect in lakes creating massive lakes and dunes.

Titan is a planet-sized hydrocarbon factory. Instead of water, vast quantities of organic chemicals rain down on the moon’s surface, pooling in huge reservoirs of liquid methane and ethane. Solid carbon-based molecules are also present in the dune region around the equator, dwarfing Earth’s total coal supplies. Carl Sagan coined the term “tholins” to describe prebiotic chemicals, and the dunes of Titan are expected to be teeming with them. Tholins are essential for the beginning of carbon-based organisms, so these new observations by Cassini will stir massive amounts of excitement for planetary physicists and biologists alike.

The cold -179°C (-290°F) landscape of Titan is currently being mapped by the Cassini probe as it orbits the ringed gas giant, Saturn. Some 20% of the moons surface has been catalogued and so far several hundred hydrocarbon seas and lakes have been discovered. These lakes, individually, have enough methane/ethane energy to fuel the whole of the US for 300 years.

These new findings have been published in the January 29th issue of the Geophysical Research Letters by Ralph Lorenz from the Cassini radar team (Johns Hopkins University Applied Physics Laboratory, USA). Lorenz said on reviewing the Cassini data that, “we know that some lakes are more than 10 m or so deep because they appear literally pitch-black to the radar. If they were shallow we’d see the bottom, and we don’t.” He also steps into the life-beyond-Earth debate by pointing out: “We are carbon-based life, and understanding how far along the chain of complexity towards life that chemistry can go in an environment like Titan will be important in understanding the origins of life throughout the universe.”

The ESA Huygens probe separated from Cassini and dropped slowly through the Titan atmosphere in January 2005 analyzing the atmospheric composition and taking some breathtaking images of the surrounding landscape. To complement the huge amount of data assembled from Huygens decent, Cassini will flyby the moon again on February 22nd to take radar data of the Huygens landing site.


Titan has Drizzling Methane Rain


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

Coastal Scene on Titan


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

Organic Chemicals Discovered in Titan’s High Atmosphere


Since the twin Voyager spacecraft flew past Saturn’s moon Titan, Scientists have been excited about what its hazy atmosphere can tell us about the earliest days of our own planet. The Voyagers discovered that Titan’s atmosphere is swirling with hydrocarbons and other complex organic molecules that could be the building blocks of life. The latest findings from NASA’s Cassini spacecraft have uncovered these organic molecules floating higher in Titan’s atmosphere than scientists originally thought possible.

This latest research has been published in the May 11, 2007 edition of the Journal Science. It shows that these organic aerosols, called tholins, have been found in altitudes higher than 1,000 kilometres (620 miles) above the surface of Titan. And these molecules are formed differently than how scientists originally believed.

This inquiry is important because the Titan’s environment is thought to be very similar to the Earth’s early history, before the first life formed. A similar process could have happened here.

Original Source: SwRI News Release

Massive Mountain Range Seen on Titan

Mountain range on Titan. Image credit: NASA/JPL/SSINew images of Titan sent back by NASA’s Cassini spacecraft show a large mountain range, extending about 150 km (93 miles) long. The mountains were seen on Cassini’s most recently flyby on October 25, 2006, where the spacecraft captured the highest resolution infrared views of Saturn’s largest moon. They reach about 1.5 km (almost 1 mile) high, and they’re probably made of icy material, and coated with many layers of organic material.
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