Low CO/CO₂ ratios of comet 67P measured at the Abydos landing site by the Ptolemy mass spectrometer

Abstract

Comets are generally considered to contain the best-preserved material from the beginning of our planetary system, although the mechanism of their formation and subsequent evolution are still poorly understood. Here we report the direct in situ measurement of H₂O, CO, and CO₂ by the Ptolemy mass spectrometer onboard the Philae lander, part of the European Space Agency's Rosetta mission, at the Abydos site of the Jupiter-family comet 67P/Churyumov-Gerasimenko. A CO/CO₂ ratio of around 0.07 ± 0.04 is found at the surface of the comet, a value substantially lower than the one measured by ROSINA in the coma. Such a major difference is a potential indication of heterogeneity of the nucleus and not of changes in the CO/CO₂ ratio of the coma with radial distance.