A $\sim$32-70 K formation temperature range for the ice grains agglomerated by comet 67P/Churyumov-Gerasimenko

TL;DR

This study uses simulations to estimate the formation temperature of ice grains in comet 67P/Churyumov-Gerasimenko, suggesting they formed between 32 and 70 K in the protosolar nebula, explaining observed N$_2$/CO ratios.

Contribution

It introduces a simulation-based method to determine the formation temperature range of cometary ice grains from clathrates, linking observed gas ratios to formation conditions.

Findings

Formation temperature range: 31.8 to 69.9 K.

N$_2$/CO ratio matches observations at these temperatures.

Clathrates could explain N$_2$ depletion in the comet.

Abstract

Grand Canonical Monte Carlo simulations are used to reproduce the N$_2$/CO ratio ranging between 1.7 $\times$ 10$^{-3}$ and 1.6 $\times$ 10$^{-2}$ observed {\it in situ} in the Jupiter family comet 67P/Churyumov-Gerasimenko by the ROSINA mass spectrometer aboard the Rosetta spacecraft, assuming that this body has been agglomerated from clathrates in the protosolar nebula. Simulations are done using an elaborated interatomic potentials for investigating the temperature dependence of the trapping within a multiple guest clathrate formed from a gas mixture of CO and N$_2$ in proportions corresponding to those expected for the protosolar nebula. By assuming that 67P/Churyumov-Gerasimenko agglomerated from clathrates, our calculations suggest the cometary grains must have been formed at temperatures ranging between $\sim$31.8 and 69.9 K in the protosolar nebula to match the N$_2$/CO ratio measured by the ROSINA mass spectrometer. The presence of clathrates in Jupiter family comets could then explain the potential N$_2$ depletion (factor up to $\sim$87 compared to the protosolar value) measured in 67P/Churyumov-Gerasimenko.