⛈️ Weather on Titan as seen by James Webb and Keck

The James Webb Space Telescope (JWST), in collaboration with the ground-based Keck II telescope, has for the first time observed cloud convection in the northern hemisphere of Titan, Saturn's largest moon.

This study, which involved researchers from IPGP, provides new insights into the atmospheric dynamics and organic chemistry of this astrobiologically significant celestial body. Conducted as part of JWST's guaranteed time observation program, it was published in the journal Nature Astronomy.

Unprecedented data to visualize Titan's atmosphere

Data collected in November 2022 and July 2023 by JWST and the W.M. Keck observatories reveal the presence of methane clouds evolving at different altitudes in Titan's northern hemisphere. Using specific infrared filters (from 1.4 to 2.17 microns), researchers were able to probe several atmospheric layers, from the lower troposphere to the stratosphere, and observe vertical cloud movement, indicating sustained convective activity.

The images notably show cloud formations rising between July 11 and 14, 2023, confirming for the first time a convection phenomenon at high northern latitudes. This type of observation represents a major contribution to understanding Titan's methane cycle and complex meteorology.

Titan: weather driven by methane

On Titan, methane plays a meteorological role analogous to water on Earth. It evaporates from lakes and seas, condenses in the atmosphere and forms clouds, occasionally falling back as rain on an icy surface.

Observations show clouds located in Titan's northern hemisphere - a region where the main methane lakes are concentrated, covering an area comparable to that of North America's Great Lakes. It is currently summer in this hemisphere. The ascent of clouds to altitudes reaching 28 miles (45 km) (compared to 7.5 miles (12 km) on Earth) illustrates the vertical dynamics of an extended atmosphere, made possible by the moon's low gravity.

A breakthrough in cryogenic organic chemistry

Alongside these meteorological observations, the study has led to a major advance in the study of Titan's organic chemistry: the detection of the methyl radical (CH₃), an unstable compound formed during methane dissociation. This molecule, previously undetected in Titan's atmosphere, is a fundamental intermediate in reaction chains producing complex hydrocarbons.

Its presence attests to Titan's chemical richness, whose atmospheric processes could shed light on conditions favorable to the emergence of life. The ability to track these reactions "in progress", rather than just their end products, represents a decisive step forward in understanding extraterrestrial organic environments.

A fragile atmospheric cycle

The study also highlights the vulnerability of Titan's methane cycle. Some methane transforms into heavier compounds that fall back to the surface; another portion is lost when hydrogen escapes into space. Without deep sources capable of reinjecting methane into the atmosphere, it could become depleted over time - a phenomenon comparable to the water loss experienced by Mars in its past.

Towards the Dragonfly mission

The results of this study are part of a scientific continuum ranging from the Cassini-Huygens mission (1997-2017) to the Dragonfly mission, planned for 2034. This NASA octocopter drone will perform successive flights on Titan's surface to explore various sites and analyze their composition.

Combined with data from major observatories (JWST, Hubble, Keck), the Dragonfly mission will significantly enhance our understanding of Titan and illuminate the physico-chemical conditions that may exist on other celestial bodies.