The 3 boulders are found in the Aker region of Comet 67P, on the comet's large lobe (boxed). Image via ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Researchers who continue to monitor the surface of Comet 67P with the Rosetta spacecraft have been left mystified as to the origins of a formation of three boulders on the comet’s surface.
The discovery was made by the OSIRIS team from the European Space Agency (ESA), which is continuing its mission to detail the comet’s topography in as much detail as possible and came across the three large rocks in images taken last year.
Similar to Earthly formations
Image of the boulders taken by OSIRIS on 16 September 2014 from a distance of 29 km. Image via ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
According to the ESA, the team does agree that it looks similar to formations that appear on Earth known as ‘balancing rocks’, which are effectively standing with minimal surface area on the ground having moved there through geological and atmospheric changes on our planet such as through wind or glaciers.
This, however, doesn’t explain how it could have happened on a planet that has no atmosphere or weather patterns.
“How this apparent balancing rock on Comet 67P/C-G was formed is not clear at this point,” said OSIRIS’ principal investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany.
Image of the boulders taken by OSIRIS on 16 August 2014 from a distance of 105 kilometres. Image via ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Imaging hard due to many variables
In terms of size, the largest of the three boulders, ‘3’, has a diameter of around 30m and appears to be perched on the rim of a small depression on Comet 67P’s surface.
Much of the comet’s surface is covered by boulders of a similar size – the largest being dubbed Cheops at 45m across – but none has formed in a formation even remotely close to this formation.
One of the major issues with identifying possible causes for the formation is that interpreting images on the comet surface is difficult and can vary depending on the viewing angle, illumination and the spatial resolution of the imagery.
The team will now hope to take more images using Rosetta to get a better look at the three rocks.
