Argon Measurement Capabilities at Comet 67P with ROSINA/DFMS

Little is known about the noble gas abundances in comets. These highly volatile gases are possible tracers of the history of cometary matter. They can help quantify the contribution of cometary impacts to terrestrial oceans and help elucidate the role of comets in the formation and evolution of planetary atmospheres. This paper focuses on argon and the capabilities to measure this noble gas with in situ measurements at comet 67P/Churyumov-Gerasimenko, the target of the European Space Agency’s spacecraft Rosetta. Argon may have been detected by remote sensing in a single Oort cloud comet and nothing is known about the isotopic abundances of argon in comets. Furthermore, no detection of argon in a Jupiter family comet has been reported to date. Comet 67P/Churyumov-Gerasimenko belongs to the group of Jupiter family comets and originates most likely in the Kuiper belt. Onboard Rosetta is ROSINA/DFMS (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis / Double Focusing Mass Spectrometer). DFMS has unprecedented mass resolution and high sensitivity and is designed to measure isotopic ratios including argon. Argon measurements using the DFMS lab model (identical to the flight model) demonstrate this capability. Most likely, DFMS will provide the first detection of argon in a Jupiter family comet and the first determination of the 36Ar/38Ar ratio at a comet.