Titan shows surprising seasonal changes

Detailed observations of Saturn’s moon Titan have now spanned 30 years, covering an entire solar orbit for this distant world. Dr Athena Coustenis from the Paris-Meudon Observatory in France has analysed data gathered over this time and has found that the changing seasons of Titan affect it more than previously thought. Dr Coustenis will present these results at the European Planetary Science Congress in Madrid on Friday 28th September.

Explains Dr Coustenis, “As with Earth, conditions on Titan change with its seasons. We can see differences in atmospheric temperatures, chemical composition and circulation patterns, especially at the poles. For example, hydrocarbon lakes form around the north polar region during winter due to colder temperatures and condensation. Also, a haze layer surrounding Titan at the northern pole is significantly reduced during the equinox because of the atmospheric circulation patterns. This is all very surprising because we didn’t expect to find any such rapid changes, especially in the deeper layers of the atmosphere.”

The main cause of these cycles is solar radiation. This is the dominant energy source for Titan’s atmosphere, breaking up the nitrogen and methane present to create more complex molecules, such as ethane, and acting as the driving force for chemical changes. Titan is inclined at around 27 degrees, similar to the Earth, meaning that the cause of seasons – sunlight reaching different areas with varying intensity due to the tilt – is the same for both worlds. Says Dr Coustenis, “It’s amazing to think that the Sun still dominates over other energy sources even as far out as Titan, over 1.5 billion kilometres from us.”

To draw these conclusions data was analysed from several different missions, including Voyager 1 (1980), the Infrared Space Observatory (1997), and Cassini (2004 onwards), complemented by ground-based observations. Each season on Titan spans around 7.5 years, while it takes 29.5 years for Saturn to orbit the Sun, so data has now been gathered for an entire Titan year, encapsulating all seasons.

Dr Coustenis explains why it is important to investigate this distant moon: “Titan is the best opportunity we have to study conditions very similar to our own planet in terms of climate, meteorology and astrobiology and at the same time a unique world on its own, a paradise for exploring new geological, atmospheric and internal processes.”