Highly unexpected Methane clouds sighted in Titan's stratosphere

NASA scientists have recently identified an unexpected high-altitude methane ice cloud on Saturn's moon Titan, that was similar to exotic clouds found far above Earth's poles.

Carrie Anderson, a Cassini participating scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study has said that the idea that methane clouds could form this high on Titan was completely new and nobody had considered that possible before.

The mysterious bit of atmospheric fluff, researchers have determined contained methane ice, which produced a much denser cloud than the ethane ice previously identified there.

The cloud in the stratosphere over Titan's north pole was similar to Earth's polar stratospheric clouds. Cassini had first spotted the cloud in 2006.

Methane clouds were already known to exist in Titan's troposphere, the lowest layer of the atmosphere. But methane clouds were thought unlikely in Titan's stratosphere.

As the troposphere would trapp most of the moisture, stratospheric clouds required in extreme cold even the stratosphere temperature of minus 333 degrees Fahrenheit (minus 203 degrees Celsius), observed by Cassini just south of the equator, had not been anticipated as frigid enough to allow the scant methane in this region of the atmosphere to condense into ice.

What Anderson and her Goddard co-author, Robert Samuelson, had noted was that temperatures in Titan's lower stratosphere were not the same at all latitudes.

Data from Cassini's Composite Infrared Spectrometer and the spacecraft's radio science instrument had shown that the high-altitude temperature near the North Pole was much colder than that just south of the equator.

It turned out that this temperature difference as much as 11 degrees Fahrenheit (minus 12 degrees Celsius) was more than enough to yield methane ice.

The mechanism for forming these high-altitude clouds appeared to be different from what happened in the troposphere earlier.

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

Scott Edgington, Cassini deputy project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Californi has added that Titan has continued to amaze with natural processes similar to those on the Earth, yet involving materials different from our familiar water and as scientists approached southern winter solstice on Titan, they would further explore how these cloud formation processes might vary with season.

The results of this study published online in the journal Icarus.