Drivers of Titan's Seasonal Change

Titan is Saturn's largest moon and has an atmosphere which is unique in the solar system. Titan's atmosphere is mainly nitrogen, with around 2% methane, which leads to a methane cycle analogous to Earth's water cycle and a very complex atmospheric chemistry. Photochemical dissociation of molecular nitrogen and methane in Titan's upper atmosphere form radicals, which form the basis of a photochemical network leading to production of a vast array of minor hydrocarbon and nitrile species. These species are extremely useful as tracers of atmospheric dynamics. In this proposal will will use observations of these minor species by Cassini, James Webb Space Telescope, and the Atacama Large Millimeter Array to investigate three key science questions about Titan's atmosphere:

1) What role to atmospheric waves play in the breakup of Titan's winter polar vortex?

2) How cold does Titan's winter polar vortex get and what drives this?

3) Are seasons symmetrical on Titan or does the eccentricity of Saturn's orbit cause hemisphere specific effects?

These questions are motivated by recent unexplained features of Titan's polar vortices, which include: anomalously cold temperatures in the winter polar vortex that are too cold to measure with existing methods; the puzzling presence of waves in the polar region, which appear to be at odds with the long-lived nature of Titan's vortices; and the suggestion of seasonal symmetry in the stratosphere which cannot be confirmed due to data gaps.

For the first time we will be able to perform a detailed analysis of the highest spatial resolution Cassini observations, which has not been possible until now as it requires an accurate knowledge of the climatology to use as a starting point for analysis. This climatology is now available from our extensive recent studies on medium resolution observations for the whole Cassini mission. We will also implement a novel inversion methodology in order to measure the cold polar temperatures accurately for the first time. The Cassini data is unparalleled in spatial resolution and coverage of the vortex, but will be extended in time to search for seasonal asymmetries using new observations from ALMA and JWST. The project will result in new insights into Titan's atmosphere in addition to revealing the fundamental physics at work in planetary atmospheres in general. This will have implications for terrestrial planet atmospheres in our own solar system and beyond.