Comet 67P/Churyumov–Gerasimenko (67P) is better known as the Rosetta comet, after the orbiting spacecraft that continues to make unprecedented discoveries.
Using the Visible Infrared and Thermal Imaging Spectrometer (VIRTIS) on board the spacecraft, Maria Cristina De Sanctis et al. have found a cyclic condensation of water on the surface of 67P, which follows solar illumination. Comparison with a thermo–physical model can explain the diurnal cycle: gas sublimates from below the surface and condenses directly onto the surface. Such a process can lead to differential erosion and may keep water ice near the surface.
This is consistent with results from the Microwave Instrument onboard the Rosetta Orbiter (MIRO) on the dark side of 67P, which had been in the dark for about five years. Thermal inertia measurements analysed by Mathieu Choukroun's team suggest ice on the surface or within tens of centimetres of the surface.
And finally, Andre Bieler et al. have reported Rosetta Orbiter Spectrometer for Ion and Neutral Analysis Double Focusing Mass Spectrometer (ROSINA DFMS) results that show levels of molecular oxygen in the coma to be too high for current models of Solar System formation. Moreover, the correlation between O2 and H2O suggests a common primordial origin.