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A gaseous envelope for many planets: the different planetary atmospheres

Because of the strong relation with the atmosphere of our planet, the study of other planetary atmospheres in our solar system is well developed at IPSL. These atmospheric systems are those of Mars and Venus of course, the dense atmosphere of Titan, satellite of Saturn, but also more tenous atmospheres such as Mercury, Triton or Pluto. These researches may also extend in the future to the study of such atmospheres on exoplanets.

As in other fields, the research is organized in three combining methodologies :

  1. Observations, with in situ measurements from orbiters, atmospheric probes or landers, ground-based observations, as well as space observatories in orbit around the Earth. These observations yields reference datasets that help understand the atmospheric systems under study. IPSL teams are involved in planetary missions: Mars-Express , Vénus-Express , Cassini-Huygens for Titan, and Bepi-Colombo for Mercury. We have also strong collaborations with observatories, especially the LESIA , in Meudon.

  2. Numerical modeling. The goal of this method is to retrieve the overall atmospheric properties of an atmosphere from basic physical and chemical laws. Therefore, we develop (in a close partnership between LMD and LATMOS) General Circulation Models, that are powerful numerical simulators used for Earth meteorological predictions as well as for studies of Earth climate. Based on an initial state (winds, pressures, temperatures) and on well known physical laws (mass, energy and momentum conservations, radiative heating and cooling, etc...), the GCM computes the global evolution of the atmosphere. The Earth GCM developed at IPSL is not based on observational results, but on physical laws. Therefore, it was possible to adapt this tool to the study of other planetary atmospheres (Mars, Venus, Titan), in order to understand these different climates, to use comparative planetology to improve our understanding of general meteorology, and to give the necessary informations for in situ exploration of these atmospheres (aerobraking, aerocapture, atmospheric entry, and so on...).

  3. Experimental simulations. For the study of planetary atmospheres, the PAMPRE (Production d'Aérosols en Microgravité par Plasma REactif) experiment is developed at LATMOS. Photochemistry in the Titan atmosphere is globally producing organic aerosols. These aerosols have a significant rôle in the climate of Titan, but very few direct data have been obtained on the physical and chemical properties of these aerosols. The PAMPRE experiment has been developed to study the formation process and the properties of these aerosols, through the production of laboratory analogs (called tholins), produced in conditions close to the ones in Titan's atmosphere. These analogs are also used as reference material in order to analyse the data obtained for the atmosphere of Titan with the experiments on board the Cassini and Huygens probes.

Titan's atmosphere

Haze (top) and clouds (bottom) opacities in Titan's atmosphere, modeled with our Titan GCM during northern winter. In the top figure, contours show the meridional circulation, while in the bottom figure, they indicate the limits of the methane clouds.
Author : Sébastien Lebonnois
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