Seasonal exposure of carbon dioxide ice on the nucleus of comet 67P/Churyumov-Gerasimenko

Abstract

Carbon dioxide (CO₂) is one of the most abundant species in cometary nuclei, but because of its high volatility, CO₂ ice is generally only found beneath the surface. We report the infrared spectroscopic identification of a CO₂ ice-rich surface area located in the Anhur region of comet 67P/Churyumov-Gerasimenko. Spectral modeling shows that about 0.1% of the 80- by 60-meter area is CO₂ ice. This exposed ice was observed a short time after the comet exited local winter; following the increased illumination, the CO₂ ice completely disappeared over about 3 weeks. We estimate the mass of the sublimated CO₂ ice and the depth of the eroded surface layer. We interpret the presence of CO₂ ice as the result of the extreme seasonal changes induced by the rotation and orbit of the comet.