On the chemical origin of volatile species in comets
Intervenant : Vianney Taquet
The Rosetta spacecraft analysed the Jupiter-family comet 67P/Churyumov-Gerasimenko (67P/C-G) in 2014 and 2015. The ROSINA mass spectrometer on board the Rosetta orbiter carried out a chemical census with unprecedented sensitivity of the coma of 67P/C-G and detected a “zoo” of molecules from simple di-atomic species to complex pre-biotic organics, such as glycine. The precise abundances and the signal correlations among species measured by Rosetta/ROSINA now give us invaluable constraints to infer the chemical origin of comet 67P/C-G, and possibly of our Solar System. In this talk, I will take the examples of molecular oxygen and deuterated organic molecules, such as methanol, whose signal correlations and abundance ratios with water ice can be used as powerful chemical tracers. We compared the ROSINA measurements with state-of-the-art astrochemical models applied to dynamical models by considering several scenarios, and with sub-mm interferometric observations of nearby low-mass protostars using the ALMA and NOEMA sub-mm interferometers. The comparison between comet measurements, model predictions and protostar observations would favour a dark cloud (or “primordial”) grain surface chemistry origin for molecular oxygen and methanol in comets, albeit for slightly warmer and denser dark clouds than those usually considered as solar system progenitors.