That sinking feeling

Cometary physical chemistry could be to blame for the presence of sinkholes on the surface of the comet 67P/Churyumov-Gerasimenko. The European Space Agency's Rosetta spacecraft first went into orbit around the comet almost one year ago (in August 2014). Scientists got a first close-up view of surprisingly deep, almost perfectly circular pits on the comet's surface. Now, a new study based on close-up photographs sent back to Earth by Rosetta suggests that these pits are sinkholes, formed through physical chemistry as the ices, comprising primarily water, carbon monoxide and carbon dioxide, beneath the comet's surface sublimate.