Cassini Probe Spots Methane Ice Crystals In Titan’s Atmosphere

Monday, November 3, 2014

Cassini Probe Spots Methane Ice Crystals In Titan’s Atmosphere

Cassini Probe Spots Methane Ice Crystals In Titan’s Atmosphere:

This cloud in the stratosphere over Titan’s north pole (left) is similar to Earth’s polar stratospheric clouds (right). NASA scientists found that Titan’s cloud contains methane ice, which was not previously thought to form in that part of the atmosphere. Cassini first spotted the cloud in 2006. Credit:
L. NASA/JPL/U. of Ariz./LPGNantes; R. NASA/GSFC/M. Schoeberl

During its 2006 flyby of Titan, the Cassini Space Probe captured some of the most detailed images of Saturn’s largest moon. Amongst them was one showing the lofty cloud formations over Titan’s north pole (shown above). Interestingly enough, these cloud formations bear a strong resemblance to those that are seen in Earth’s own polar stratosphere.

However, unlike Earth’s, these clouds are composed entirely of liquid methane and ethane. Given Titan’s incredibly low temperatures – minus 185 °C (-300 °F) – it’s not surprising that such a dense atmosphere of liquid hydrocarbons exists, or that seas of methane cover the planet.

What is surprising, however, is the fact that methane crystals also exist in this atmosphere. Eight years after the photos of Titan’s north pole were taken, astronomers have concluded that this region also contains trace amounts of methane ice.

“The idea that methane clouds could form this high on Titan is completely new,” said Carrie Anderson, a Cassini participating scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study. “Nobody considered that possible before.”

Other stratospheric clouds had been identified on Titan already, including clouds of ethane – a chemical formed after methane breaks down. Delicate clouds of cyanoacetylene and hydrogen cyanide, which form from reactions of methane byproducts with nitrogen molecules, have also been found there.

But clouds of frozen methane were thought unlikely in Titan’s stratosphere. Because the troposphere traps most of the moisture, stratospheric clouds require extreme cold. Even the stratosphere temperature of minus 203 °C (-333 °F), observed by Cassini just south of the equator, was not cold enough to allow the scant methane in this region of the atmosphere to condense into ice.

A composite image of Titan’s atmosphere, created using blue, green and red spectral filters to create an enhanced-color view. Image Credit: NASA/JPL/Space Science Institute

What Anderson and her Goddard co-author, Robert Samuelson, noted is that temperatures in Titan’s lower stratosphere are not the same at all latitudes. This was based on data taken from Cassini’s Composite Infrared Spectrometer and the spacecraft’s radio science instrument, which showed that the high-altitude temperature near the north pole was much colder than that just south of the equator.

It turns out that this temperature difference – as much as 6 °C (11 °F) – is more than enough to yield methane ice.

Other observations made of Titan’s cloud system support this conclusion, such as how certain regions appear denser than others, and the larger particles detected are the right size for methane ice. They also confirmed that the expected amount of methane – 1.5%, which is enough to form ice particles – is present in the lower polar stratosphere.

What’s more, the observation confirms certain models of how Titan’s atmosphere is thought to work.

According to this model, Titan has a global circulation pattern in which warm air in the summer hemisphere wells up from the surface and enters the stratosphere, slowly making its way to the winter pole. There, the air mass sinks back down, cooling as it descends, which allows the stratospheric methane clouds to form.

“Cassini has been steadily gathering evidence of this global circulation pattern, and the identification of this new methane cloud is another strong indicator that the process works the way we think it does,” said Michael Flasar, Goddard scientist and principal investigator for Cassini’s Composite Infrared Spectrometer (CIRS).

Like Earth’s stratospheric clouds, Titan’s methane cloud was located near the winter pole, above 65 degrees north latitude. Anderson and Samuelson estimate that this type of cloud system – which they call subsidence-induced methane clouds (or SIMCs for short) – could develop between 30,000 to 50,000 meters (98,000 to 164,000 feet) in altitude above Titan’s surface.

“Titan continues to amaze with natural processes similar to those on the Earth, yet involving materials different from our familiar water,” said Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “As we approach southern winter solstice on Titan, we will further explore how these cloud formation processes might vary with season.”

The results of this study are available online in the November issue of Icarus.

Further Reading: NASA/GSC

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The National Aeronautics and Space Administration (NASA) is the United States government agency responsible for the civilian space program as well as aeronautics and aerospace research. President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA's predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

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The Oxford English Dictionary defines a UFO as "An unidentified flying object; a 'flying saucer'." The first published book to use the word was authored by Donald E. Keyhoe. The acronym "UFO" was coined by Captain Edward J. Ruppelt, who headed Project Blue Book, then the USAF's official investigation of UFOs. He wrote, "Obviously the term 'flying saucer' is misleading when applied to objects of every conceivable shape and performance. For this reason the military prefers the more general, if less colorful, name: unidentified flying objects. UFO (pronounced Yoo-foe) for short." Other phrases that were used officially and that predate the UFO acronym include "flying flapjack", "flying disc", "unexplained flying discs", "unidentifiable object", and "flying saucer". The phrase "flying saucer" had gained widespread attention after the summer of 1947. On June 24, a civilian pilot named Kenneth Arnold reported seeing nine objects flying in formation near Mount Rainier. Arnold timed the sighting and estimated the speed of discs to be over 1,200 mph (1,931 km/h). At the time, he described the objects' shape as being somewhat disc-like or saucer-like, leading to newspaper accounts of "flying saucers" and "flying discs". In popular usage the term UFO came to be used to refer to claims of alien spacecraft. and because of the public and media ridicule associated with the topic, some investigators prefer to use such terms as unidentified aerial phenomenon (or UAP) or anomalous phenomena, as in the title of the National Aviation Reporting Center on Anomalous Phenomena (NARCAP).

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UFO - Unidentified Flying Object An unidentified flying object, or UFO, in its most general definition, is any apparent anomaly in the sky that is not identifiable as a known object or phenomenon. Culturally, UFOs are associated with claims of visitation by extraterrestrial life or government-related conspiracy theories, and have become popular subjects in fiction. While UFOs are often later identified, sometimes identification may not be possible owing to the usually low quality of evidence related to UFO sightings (generally anecdotal evidence and eyewitness accounts). Stories of fantastical celestial apparitions have been told since antiquity, but the term "UFO" (or "UFOB") was officially created in 1953 by the United States Air Force (USAF) to serve as a catch-all for all such reports. In its initial definition, the USAF stated that a "UFOB" was "any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type, or which cannot be positively identified as a familiar object." Accordingly, the term was initially restricted to that fraction of cases which remained unidentified after investigation, as the USAF was interested in potential national security reasons and/or "technical aspects" (see Air Force Regulation 200-2). During the late 1940s and through the 1950s, UFOs were often referred to popularly as "flying saucers" or "flying discs". The term UFO became more widespread during the 1950s, at first in technical literature, but later in popular use. UFOs garnered considerable interest during the Cold War, an era associated with a heightened concern for national security. Various studies have concluded that the phenomenon does not represent a threat to national security nor does it contain anything worthy of scientific pursuit (e.g., 1951 Flying Saucer Working Party, 1953 CIA Robertson Panel, USAF Project Blue Book, Condon Committee).

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Photos of Nature | Nature Photography What is The Universe

Monday, November 3, 2014