Comet 67p sinkholes throw origin of comets into question

2 Jul 2015

Much like Earth, the surface of Comet 67p appears to experience the phenomenon of sinkholes, with new photos taken by the Rosetta spacecraft throwing the origin of comets into question.

Using Rosetta’s OSIRIS camera, the monitoring team from the European Space Agency (ESA) were able to determine that these holes, once thought of as the aftermath of a small meteorite collision, are actually sinkholes created in exactly the same way as here on Earth.

In a study published to Nature, the team has found 18 quasi-circular pits just in the northern hemisphere of the comet, all measuring from a few tens to a few hundreds of metres in depth (up to 210m) to a smooth, dust-covered sinkhole floor.

While their appearance is similar to Earth’s sinkholes, which are created by a weakening of the ceiling of a subsurface cavity becoming too thin to support its own weight and collapses, their formation is still yet to be determined, with three most-likely options determined by ESA’s researchers.

The first being that these sinkholes have existed since its formation with slow-speed collisions un-evenly forming chunks into one large comet.

The evolution of sinkholes on Comet 67p

From left to right, we see the active sinkhole, compared with the inactive sinkhole on the far-right. Image via ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The two other possible theories suggest that sublimation of pockets of carbon dioxide and carbon monoxide occurred when exposed to sunlight or equally could be driven by the energy liberated by water ice changing its physical state from amorphous to crystalline then sublimating the more volatile surrounding carbon dioxide and carbon monoxide ices.

The researchers are particularly interested in observing the active holes whose sides are much steeper compared with older sinkholes, which are now filled with dust.

By analysing the sinkholes, they believe they will be able to determine the age of the comet’s surface.

“We think that we might be able to use the pits to characterise the relative ages of the comet’s surface: the more pits there are in a region, the younger and less processed the surface there is,” said Jean-Baptiste Vincent from the Max Planck Institute for Solar System Research and lead author of the study.

Colm Gorey was a senior journalist with Silicon Republic