The Cassini spacecraft detected a massive storm developing on Titan, Saturn’s largest moon. Carrie Anderson, the lead researcher, will be presenting the discovery at the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society at National Harbor in Maryland today.

What Cassini detected was a large ice cloud in the stratosphere over Titan’s south pole, which is currently on its winter phase. There was a first sighting of an enormous ice cloud on the moon’s stratosphere with an altitude of approximately 300km, but the spacecraft later spotted a larger cloud floating under the former one, this time with around 200km of altitude. According to Anderson, the latter ice cloud presents about 5 degrees in latitude and it may have a lower density than the first one.

According to NASA, as winter sets in at Titan’s south pole, a cloud system called the south polar vortex (small, bright “button”) has been forming. Credit: NASA

The probe managed to spot the clouds thanks to its Composite Infrared Spectrometer (CIRS), which is able to detect infrared wavelengths that the human eye can’t.

This large ice cloud resembles the Earth’s fog, however, it appears to be flat on top.

Differently than the clouds on Earth, which form the evaporation of water into the air, Titan’s clouds form from warm gasses (located at the warm pole) traveling to the cold pole, where those gasses freeze and consequently create ice clouds. The clouds begin freezing at different temperatures as they move from one pole to another, which is the way different layers of these clouds are formed.

Cassini has been on Titan since the mission started back in 2004. Ever since then, the spacecraft has witnessed spring and summer at the moon’s north pole, along with fall and the current winter at its south pole. Each season on Saturn’s largest moon lasts close to 7 and a half years for Earth’s standards, so its south pole will still be on winter by the time the Cassini mission ends in a few years.

“Titan’s seasonal changes continue to excite and surprise. Cassini, with its very capable suite of instruments, will continue to periodically study how changes occur on Titan until its Solstice mission ends in 2017,” said Scott Edgington, a scientist taking part on the Cassini deputy project  at NASA’s Jet Propulsion Laboratory.

Robert Samuelson, a researcher from the Goddard Space Flight Center working with Anderson, pointed out that findings so far indicate that the early stages of Titan’s southern winter make it seem way more severe than those of the moon’s northern winter.

Currently, there are more clouds developing at the satellite’s south pole, which might forecast a shift on Titan’s global circulation.

Source: NASA