THE APSIS EXPERIMENT: SIMULATING TITAN'S UPPER ATMOSPHERE AND ITS PHOTOCHEMISTRY IN THE VACUUM ULTRA-VIOLET (VUV)

International audienceTitan, the largest moon of Saturn, has a dense atmosphere whose upper layers are mainly composed of methane (CH4) and molecular nitrogen (N2). The Cassini mission revealed that the interaction between those molecules and the solar VUV photons, as well as the electrons from Saturn’s magnetosphere, leads to a complex chemistry.Moreover, this naturally ionized environment contains heavy organic molecules like benzene (C6H6) even at altitudes higher than 900 km.The presence of those molecules makes Titan a natural laboratory to witness and understand prebiotic-like chemistry but despite all the data collected, all the possible chemical processes in such a hydrocarbon-nitrogen-rich environment are not precisely understood. This is why Titan’s atmosphere simulation experiments are of high interest. We designed a gas reactor named APSIS for Atmospheric Photochemistry SImulated by Synchrotron which is to be coupled with a VUV photon source as N2 needs wavelengths shorter than 100 nm in order to be dissociated. The aim is to understand the key processes in the formation of those heavy compounds. We will present here our first experimental results obtained with APSIS coupled with this surfatron and then discuss them regarding the Cassini data, previous laboratory experiments and numerical models