High D/H ratios in water and alkanes in comet 67P/Churyumov-Gerasimenko measured with Rosetta/ROSINA DFMS

Vol. 662
10. Planets and planetary systems

High D/H ratios in water and alkanes in comet 67P/Churyumov-Gerasimenko measured with Rosetta/ROSINA DFMS

by D. R. Müller, K. Altwegg, J.J. Berthelier, et al. 2022, A&A, 662, A69 alt

Measurements of isotopic abundances in comets bear key information regarding the early Solar System’s composition and physical conditions. Thanks to its sensitivity and mass resolution, the mass spectrometer ROSINA/DFMS onboard Rosetta had the capability to detect tens of new atomic and molecular species in comet 67P/Churyumov-Gerasimenko and to measure isotopic ratios in many of them. Here, Müller et al. present two sets of new results. First, they show that the D/H ratio in water, which is enhanced by a factor 3.2 over the terrestrial value, is independent of heliocentric distance, the level of cometary activity, and the distance to the nucleus; the same is true for the 16O/17O ratio. More remarkably, they also measured for the first time in comets the D/H ratios in a suite of alkanes (CH4, C2H6, C3H8, and C4H10). The inferred values are 4-5 times enhanced over the D/H ratio in water, but comparable to its value in several other carriers, the most noteworthy one being in the organic refractory component of 67P dust. This suggests that these organic molecules may be inherited from the presolar molecular cloud, where ionized radiation in cold environments favored D/H fractionation, both in water and (differentially) in organics. In contrast, the 13C/12C ratio in 67P's alkanes is found to be consistent with the 13C/12C ratio on Earth and other planets, adding further evidence for a "universal" Solar System 13C/12C value.