NASA's Cassini Shows Noticeable Climatic Changes on Titan

With the help of NASA's Cassini spacecraft, scientists have observed a noticeable climatic change in the southern hemisphere of Saturn's giant moon 'Titan'.

Since 2004 NASA's Cassini spacecraft has been orbiting Saturn. But for the first time scientists have been able to observe the seasonal atmospheric circulation direction change on Titan. This sort of an event occurs once every 15 years and is never observable from Earth. 

Since the Titan's rotation axis is tilted at a similar angle  to that of Earth, it witnesses similar seasons but at a much more relaxed pace as Saturn takes 29.5 Earth years to orbit the Sun.

With the help of infrared spectra measured by Cassini's Composite InfraRed Spectrometer (CIRS), Dr Nick Teanby of the University of Bristol along with his colleagues determined the atmospheric temperature and global distributions of chemical tracers. Doing so helped them to chart the seasonal changes that are occurring on Titan in a more detailed manner.

A major increase in Titan's exotic trace gases over the south pole  was observed by the team. This occurred in a relatively short time. These trace gases are produced high in Titan's atmosphere, where sunlight and highly energetic particles break down nitrogen and methane and recombine to form a vast array of more complex molecules like benzene and hydrogen cyanide.

Co-author, Dr Remco de Kok of SRON Netherlands Institute for Space Research said: "We were waiting for signs that the trace gas abundances would change together with the new season, but we did not expect such a large and rapid change: some gas concentrations increased more than a thousand times within only a few months. Also surprising was that this was happening at altitudes above 450 km, much higher than initially anticipated."

Lead author, Dr Nick Teanby of Bristol's School of Earth Sciences said: "Using measurements of temperature and chemical tracers by Cassini, we were able to observe changes in the subtle vertical winds and reveal the pole-to-pole circulation cell. For the first time ever, we observed the circulation cell direction reverse over the South Pole around the time of the 2009 southern autumnal equinox. The resulting distribution of gases shows that the circulation must extend much further than previously thought to 600 km or even higher. This calls into question our current understanding of how Titan's atmosphere works and suggests new avenues to explore."

"Our results provide a powerful new constraint for atmospheric models of Titan. Titan provides a natural laboratory for an Earth-like atmosphere in the cold outer solar system. So, these results could eventually lead to a more complete understanding of atmospheric processes on Earth, other Solar System planets, and the many exoplanetary systems now being discovered."

 In the coming years, Cassini will continue to observe how the seasons develop. Dr Conor Nixon at NASA Goddard Space Flight Centre said: "These results are giving us the first detailed look at changes occurring in Titan's atmosphere around the time of equinox, a season which has not been viewed up close by a spacecraft previously. This shows the really great science that is coming out of the Cassini extended mission phases since 2008, and we look forward to seeing the further changes that will occur over the next five years until the end of mission in 2017."

Their findings are published in Nature.