Trapping mechanism of O2in water ice as first measured by Rosetta spacecraft

Abstract

One of the most surprising measurements of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument on the comet 67P/Churyumov-Gerasimenko was the detection of O2 along with N2 and noble gases which were measured for the first time in comets, along with the major constituents, water, CO, and CO2. The O2 high abundance of 1-10 per cent relative to H2O was calculated, with an average value of 3.80 ± 0.85 per cent (Bieler et al. 2015). The strong correlation of molecular oxygen abundance with water, suggests the formation of O2 by radiolysis or photolysis of water molecules and the trapping of O2 in the amorphous ice, together with the other gases while the comet was formed. In this study, we present new experimental results for trapping O2 with N2 and Ar in amorphous ice in order to understand the direct measurements of the Rosetta spacecraft. The discovery of O2 in comets challenges our understanding of the composition of the volatiles in the outskirts of the young solar system and their delivery to the Earth's atmosphere.