The Ice Composition Close to the Surface of Comet 67P/Churyumov-Gerasimenko

Abstract

The relation between ice composition in the nucleus of comet 67P/Churyumov-Gerasimenko on the one hand and relative abundances of volatiles in the coma on the other hand is important for the interpretation of density measurements in the environment of the cometary nucleus. For the 2015 apparition, in situ measurements from the two ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) sensors COPS (COmet Pressure Sensor) and DFMS (Double Focusing Mass Spectrometer) determined gas densities at the spacecraft position for the 14 gas species H2O, CO2, CO, H2S, O2, C2H6, CH3OH, H2CO, CH4, NH3, HCN, C2H5OH, OCS, and CS2. We derive the spatial distribution of the gas emissions on the complex shape of the nucleus separately for 50 subintervals of the 2 year mission time. The most active patches of gas emission are identified on the surface. We retrieve the relation between solar irradiation and observed emissions from these patches. The emission rates are compared to a minimal thermophysical model to infer the surface active fraction of H2O and CO2. We obtain characteristic differences in the ice composition close to the surface between the two hemispheres with a reduced abundance of CO2 ice on the northern hemisphere (locations with positive latitude). We do not see significant differences for the ice composition on the two lobes of 67P/C-G.

The Return of the Rosetta Target: Keck Near-infrared Observations of Comet 67P/Churyumov–Gerasimenko in 2021

“…The distributions on both dates are consistent with a fan-shaped coma, approximately oriented toward the Sun, as observed by Rosetta (Biver et al 2019;Cheng et al 2022). This suggests similar outgassing patterns in 2015 and 2021 during equivalent R h (postperihelion) and season, when outgassing occurred mainly from regions in the cometʼs southern hemisphere, while preferentially exposed to the Sun (Läuter et al 2022).…”

“…For such species we justify the assumptions for their GF. We adopt the same GF for H 2 O and CH 3 OH, assuming that the outgassing of these volatiles near perihelion is sourced in similar regions of the nucleus (Biver et al 2019;Läuter et al 2022). We assume the same ratio between the growth factors of C 2 H 6 and H 2 O in the KL1 setting (where both are measured) applies to the KL2 setting (where a GF could be measured only for H 2 O), thereby allowing us to calculate the GF for C 2 H 6 in KL2.…”

Nitrile regio-synthesis by Ni centers on a siliceous surface: implications in prebiotic chemistry

“…Here, we have hypothesized an environment relatively rich in H, CN, CO and unsaturated organic substrates as observed in patches on 67P/Churyumov-Gerasimenko and other comets. [47][48][49] In the 2 nd reaction step, H addition, one propene molecule must be replaced by an atomic H resulting in a 1e À change. The total reaction is energetically favored by DG = À39.6 kcal mol À1 with a barrierless addition of H to the Ni center (see ESI †).…”