TLALOC · Titan’s Lakes and Lower Clouds: investigation of the enigmatic methane cycle with a new advanced model.

Titan’s Lakes and Lower Clouds: investigation of the enigmatic methane cycle with a new advanced model.

Titan, Saturn’s largest moon, is the only place beyond Earth that hosts a hydrological cycle. At Titan’s surface at -180ºC, the flowing element is methane. The Cassini-Huygens mission brought unprecedented insights on this methane cycle, with radar cartography of many methane lakes at the poles, images of clouds and riverbeds, and proofs of rain. However, this cycle is not completely understood. Open questions remain on the presence of methane reservoirs and on why global climate models do not fairly reproduce clouds and rain. The goal of TLALOC was to develop a competitive Titan system model in collaboration with the U.S. (SwRI) and two E.U. laboratories (UPV/EHU and LMD/Sorbonne University) in order to close key scientific knowledge gaps about Titan’s methane cycle. To better understand the methane cycle, we investigated key physical process (evaporation, cloud condensation, precipitation) with a mesoscale climate model. We started from an Earth atmospheric model (the Weather Research Forecast model, WRF) and modify it to feature Titan’s extreme conditions. This work also improves our knowledge on the climate models used for the Earth their limits. The NASA Dragonfly mission will explore Titan’s surface by the mid 2030s with a large instrumented drone. Having an advanced mesoscale model of Titan will be fundamental to drive the mission operations and understand many of the atmospheric measurements. The TLALOC project aimed to: (1) quantify the effect of lakes and wetlands on the local atmospheric moisture; (2) characterize the effect of solar insolation on the methane cycle at the local scale; (3) understand the formation mechanism and dynamical evolution of storm systems; and (4) confront local and global atmospheric conditions predicted by the models to Cassini and Earth-based observations. The main conclusion from this project is that lakes strongly affect their environment. Methane evaporation cools down the lake surface by 2°C compared to the shore, creating continual winds from the lake to the land with diurnal and seasonal variations. The cold humid marine above the lake enables the formation of fog as observed from Cassini data. The marine layer slows down the evaporation of the lake and decreases the formation of clouds and precipitations in Global Climate Models to values closer to observations.

Data: CORDIS, © European Union