Springtime on Titan
Together with Saturn in its 30-years orbit around the Sun, Titan has seasons that last for 7 terrestrial years. The team has observed significant atmospheric changes between July 2004 (early summer in the southern hemisphere) and April 2010, the very start of northern spring. The images showed that cloud activity has recently decreased near both of Titan’s poles. These regions had been heavily overcast during the late southern summer until 2008, a few months before the equinox.
The team has used results from the Global Climate Models (GCMs) developed by Pascal Rannou (Institut Pierre Simon Laplace) to interpret the evolution of the observed cloud patterns over time. Northern polar clouds of ethane form in Titan’s troposphere during the winter at altitudes of 30-50 km by a constant influx of ethane and aerosols from the stratosphere. In the other hemisphere, mid- and high-latitudes clouds are produced by the upwelling from the surface of air enriched in methane. Observations of the location and activity of Titan’s clouds over long periods are vital in developing a global understanding of Titan’s climate and meteorological cycle.
Since Cassini reached Saturn, VIMS has acquired more than 20,000 images of Titan. The VIMS instrument consists of two detectors, one that maps in visible wavelengths and the other that maps in infrared, which also gather spectral information about the composition of observed targets.
“Even having eliminated 90% of the images, we were still left with several million spectra to analyze. We developed a computer program that picked out the cloudy pixels and we then went back and visually checked the detections to make sure that they were relevant,” said Dr. Rodriguez.
In February 2010, the Cassini mission was extended to a few months past Saturn’s northern summer solstice in May 2017. This means that Rodriguez and his team will be able to observe seasonal changes right the way through from mid-winter to mid-summer in the northern hemisphere.
“We have learned a lot about Titan’s climate since Cassini arrived in at Saturn, but there is still a great deal to learn. With the new mission extension, we will have the opportunity to answer some of the key questions about the meteorology of this fascinating moon,” said Rodriguez.
Studying the dynamic environment of Titan is of interest to astrobiologists because some scientists have put forward theories for the potential habitability of the Saturnian moon. Titan is the only body in the Solar System aside from Earth that is known to have liquid lakes and seas on its surface. However, Titan is brutally cold, and these lakes are formed from liquid methane and ethane instead of liquid water. If life does exist on Titan, it would likely be dramatically different than the types of organisms we see on planet Earth.