New photos of the comet 67P/Churyumov-Gerasimenko have revealed sinkholes hundreds of metres deep that scientists say can't have been created by impacts.
The European Space Agency's Rosetta probe is currently orbiting 67P, while its lander Philae is on the irregularly shaped comet's surface.
What's causing them remains a mystery, but according to an article in today's issue of journal Nature, experiments and computer modelling have shown they can't be the result of impacts from smaller objects floating through space.
"Alternative mechanisms like explosive activity have been suggested, but the driving process remains unknown," scientists from the Max-Planck Institute for Solar System Research wrote.
Jets of material have been detected coming out of the pits in a number of explosive outbursts, but the amount coming out are "too small to create the observed pits" themselves.
Instead, it's theorised the holes are formed when the ceiling of a subsurface cavity becomes too weak to hold the material above it and collapses inwards. The pits then slowly get bigger as the walls sublimate – turn from solid directly into a gas.
"Because the size of sinkholes depends on the material strength of the top layers, sinkholes in a given terrain are all of similar size. They are characterised by circular depressions aligned with the local gravity vector."
This suggests the comet's surface is constantly evolving, and its constituent materials are diverse and heterogeneous.
"The crust should be relatively new where the surface is ragged with many pits, in comparison to where the surface is smoother and the pits are larger.
"The size and spatial distribution of the pits implies large differences in the physical, structural, or compositional properties of the first few hundred metres below the current surface, they conclude."
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source: newshub archive
