Ludovic Vettier

Water formation in the upper atmosphere of the early Earth

The water concentration and distribution in the early Earths atmosphere are important parameters that contribute to the chemistry and the radiative budget of the atmosphere. If the atmosphere above the troposphere is generally considered as dry, photochemistry is known to be responsible for the production of numerous minor species. Here we used an experimental setup to study the production of water in conditions simulating the chemistry above the troposphere of the early Earth with an atmospheric composition based on three major molecules: N2, CO2, and H2. The formation of gaseous products was monitored using infrared spectroscopy. Water was found as the major product, with approximately 10% of the gas products detected. This important water formation is discussed in the context of the early Earth.

In situ investigation of neutrals involved in the formation of Titan tholins

The Cassini Mission has greatly improved our understanding of the dynamics and chemical processes occurring in Titans atmosphere. It has also provided us with more insight into the formation of the aerosols in the upper atmospheric layers. However, the chemical composition and mechanisms leading to their formation were out of reach for the instruments onboard Cassini. In this context, it is deemed necessary to apply and exploit laboratory simulations to better understand the chemical reactivity occurring in the gas phase of Titan-like conditions. In the present work, we report gas phase results obtained from a plasma discharge simulating the chemical processes in Titans ionosphere. We use the PAMPRE cold dusty plasma experiment with an N2-CH4 gaseous mixture under controlled pressure and gas influx. An internal cryogenic trap has been developed to accumulate the gas products during their production and facilitate their detection. The cryogenic trap condenses the gas-phase precursors while they are forming, so that aerosols are no longer observed during the 2h plasma discharge. We focus mainly on neutral products NH3, HCN, C2H2 and C2H4. The latter are identified and quantified by in situ mass spectrometry and infrared spectroscopy. We present here results from this experiment with mixing ratios of 90-10% and 99-1% N2-CH4, covering the range of methane concentrations encountered in Titans ionosphere. We also detect in situ heavy molecules (C7). In particular, we show the role of ethylene and other volatiles as key solid-phase precursors.

Organic chemistry in a CO 2 rich early Earth atmosphere

Abstract The emergence of life on the Earth has required a prior organic chemistry leading to the formation of prebiotic molecules. The origin and the evolution of the organic matter on the early Earth is not yet firmly understood. Several hypothesis, possibly complementary, are considered. They can be divided in two categories: endogenous and exogenous sources. In this work we investigate the contribution of a specific endogenous source: the organic chemistry occurring in the ionosphere of the early Earth where the significant VUV contribution of the young Sun involved an efficient formation of reactive species. We address the issue whether this chemistry can lead to the formation of complex organic compounds with CO2 as only source of carbon in an early atmosphere made of N2, CO2 and H2, by mimicking experimentally this type of chemistry using a low pressure plasma reactor. By analyzing the gaseous phase composition, we strictly identified the formation of H2O, NH3, N2O and C2N2. The formation of a solid organic phase is also observed, confirming the possibility to trigger organic chemistry in the upper atmosphere of the early Earth. The identification of Nitrogen-bearing chemical functions in the solid highlights the possibility for an efficient ionospheric chemistry to provide prebiotic material on the early Earth.