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Professor Caitlin Griffith of the Lunar and Planetary Laboratory will discuss "Investigations of Titan's Methane Cycle."

On Titan, methane exists as a gas, liquid and solid, and cycles between the atmosphere and surface. Similar to Earth’s hydrological cycle, Titan sports clouds, rain and lakes. Yet, Titan’s cycle differs dramatically from its terrestrial counterpart, and reveals the workings of weather in an atmosphere that is 10 times thicker than Earth’s atmosphere, two orders of magnitude less illuminated, and that involves a different condensable.

Cassini/Huygens measurements of Titan's troposphere, where the methane cycle plays out, are limited to spectral images of Titan's clouds, several temperature profiles and one vertical profile of Titan's methane abundance, measured on a summer afternoon in Titan's tropical atmosphere.

Griffith will discuss thermodynamic and radiative transfer analyses of these data sets along with recent ground-based Keck spectra. These observations, albeit few, suggest that Titan's weather, climate and surface-to-atmosphere exchange of volatiles differs from the manifestation of these processes on Earth, largely as a result of different basic characteristics of these planetary bodies.

The talk ends with a comparison of Titan's and Earth's tropospheres, their fundamental properties and the energetics of their condensable cycles.