The Evolution of Activity and Chemical Composition in Rosetta’s Comet Targets Across Multiple Apparitions: Evidence for Additional CS Parents in Comet Nuclei

Jupiter family comets (JFCs) are ephemeral small bodies injected into the inner solar system from the Kuiper Belt, doomed to either sublimate all their volatiles and become inert or violently shatter from the activity. We investigate two target candidates of the ESA Rosetta mission, comets 46P/Wirtanen and 67P/Churyumov-Gerasimenko, which had favorable apparitions for Earth-based observations in 20 2018-2019 and 2021, respectively. Using the Hubble Space Telescope STIS and COS instruments we characterized the H2O and the CS2 ( assumed to be the sole parent of CS) production rates, established Afρ values, and placed upper limits on the production rate of the C2 parent. We find CS2/H2O relative abundances that are consistent with previous remote measurements of 46P and 67P. However, we find that for 67P the remote derivations of CS2/H2O ratios are substantially (∼50×) higher than the values measured by the ROSINA mass spectrometer on board the Rosetta spacecraft. We provide several hypotheses to explain this discrepancy and detail future investigations to address them.