… at least according to the Rosetta Probe:
The Rosetta space probe has spotted a square-kilometre field of solid ice in the neck region of comet 67P/Churyumov-Gerasimenko. The comet’s day-night cycle drives its small weather system using the ice field, sublimating the ice into vapour when the sun rises.
The ice was spotted in data gathered last August using Rosetta’s VIRTIS instrument – a spectrometer designed to map the comet’s chemical composition. The water signal was stronger when the neck was in shadow and weaker during the comet’s day.
(NewScientist 26 September 2015, paywall)
