ABSTRACT
We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of the mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively 'well-behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit to orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends-in this paper, we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies.This article is part of the themed issue 'Cometary science after Rosetta'.
ABSTRACT
A reliable model for the composition and evolution of interstellar ices in regions of active star formation is fundamental to our quest to determine the organic inventory of planetesimals in the early Solar System. This has become a realistic goal since the launch of the Infrared Space Observatory, which provides a facility for infrared spectroscopy unhindered by telluric absorption over the entire spectral range of vibrational modes in solids of exobiological interest. Interstellar molecules detected in the solid phase to date include H2O, NH3, CO, CO2, CH3OH, CH4, H2CO, OCS and HCOOH, together with a C identical to N-bonded absorber generically termed 'XCN'. In this article, we focus on cosmic synthesis of CN-bearing species, as this important class of prebiotic molecules may not have formed endogenously in significant quantities on early Earth if conditions were not highly reducing. Experiments in which interstellar ice analogs are subject to UV photolysis or energetic ion bombardment yield CN-rich residues with a spectral signature that matches a corresponding feature observed in young protostars enshrouded in dust and gas. CN-bearing species are also present in cometary ices, with a combined abundance comparable to the lower end of the range observed in protostars. Energetic processing of interstellar ices is thus a viable and potentially significant source of CN compounds in protoplanetary disks.
