Cameras on the Rosetta spacecraft have spotted a series of enormous pits on comet 67P/Churyumov-Gerasimenko that plunge hundreds of metres down into the body’s cold interior.
Scientists on the mission believe the pits formed in the same way as sinkholes on Earth, which appear out of the blue when the natural ceilings above underground caverns suddenly collapse under their own weight.
The comet pits are typically 200 metres across and reach down about the same distance into the comet’s body. Some of the holes may have formed in the distant past, but the walls of others are jagged and show no signs of erosion, suggesting they formed very recently.
The discovery of sinkholes shows that comets have substantial variations in their internal structure, a finding that rules out some theories of how the bodies form in the first place, from rubble left over from the birth of the solar system.
“Many comet formation models predict that under the surface they should be homogenous, the same throughout, but we show that this cannot be the case,” said Jean-Baptiste Vincent at the Max Planck Institute for Solar System Research in Göttingen.