Seasons On Titan Have A Dramatic Effect On Its Atmosphere

Titan’s south polar vortex. NASA/JPL-Caltech/Space Science Institute.

Saturn’s largest moon Titan is an incredible environment with lakes of liquid hydrocarbons, methane clouds, and a nitrogen atmosphere. It’s the only satellite to have a dense atmosphere and, according to the latest research, it experiences dramatic changes every season.

The study, published in the journal Icarus, found that winter takes hold more quickly, generating a large stratospheric vortex around the pole and kick-starting the production of complex hydrocarbons. All the data was obtained by the Cassini spacecraft, a joint ESA-NASA mission, which has been studying the Saturnian system since 2004.  

“Cassini’s long mission and frequent visits to Titan have allowed us to observe the pattern of seasonal changes on Titan, in exquisite detail, for the first time,” said team leader Dr Athena Coustenis, of the Paris Observatory, in a statement.

“We arrived at the northern mid-winter and have now had the opportunity to monitor Titan’s atmospheric response through two full seasons. Since the equinox, where both hemispheres received equal heating from the Sun, we have seen rapid changes.”

The researchers have observed a pole-to-pole circulation cycle. Warm gases rise from the summer pole while falling at the winter pole, with a large-scale inversion witnessed by the probe during the equinox in 2009.

Although the seasonality of Titan depends on global factors, the scientists have noticed that the two hemispheres react differently to the different seasons. The onset of winter caused a quick and dramatic temperature drop of 40°C (72°F) in the southern hemisphere, while the temperatures in the northern hemisphere (which was then experiencing spring) stay unchanged for the first five years.

Months after the equinox, the polar vortex started and within this atmospheric phenomenon, safe from ultraviolet light from the Sun, complex molecules can form.

Titan gets about 1 percent of the light our planet receives from the Sun, but the thick atmosphere generates a greenhouse effect, making the moon warmer than expected, although it is still significantly below freezing.

“As we count down to the end of the Cassini mission in September 2017, a consistent picture of Titan’s middle and upper atmospheres is emerging,” said Coustenis. “The 13-year total mission duration will, in the end, provide us with coverage of almost half a Titan year and provide an even deeper understanding of Titan’s seasonal variability.”

These findings were presented at the joint 48th meeting of the American Astronomical Society’s Division for Planetary Sciences and 11th European Planetary Science Congress.


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