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Birkbeck scientists record major comet cliff collapse

A 230-tonne boulder gives new insight into the processes that drive change on a comet’s surface.

The 'bouncing boulder' on Comet 67P/Churyumov-Gerasimenko
The 'bouncing boulder' on Comet 67P/Churyumov-Gerasimenko. Credit: European Space Agency

Research by Birkbeck scientist Dr Ramy El-Maarry and undergraduate student Graham Driver has resulted in the discovery of what may be the largest cliff collapse on Comet 67P/Churyumov–Gerasimenk, which was investigated by the European Space Agency’s Rosetta mission.

El-Maarry and Driver had been busy analysing images of the comet, examining how its surface at its closest approach to the Sun - a point known as perihelion - compares with its surface after this most active phase.

Dr El-Maarry, who recently collaborated on NASA’s New Horizons flyby of the Kuiper Belt Object nicknamed Ultima Thule, the most distant object ever explored, explained the significance of the findings at the EPSC-DPS conference in Geneva, Switzerland.

He said: “This seems to be one of the largest cliff collapses we’ve seen on the comet during Rosetta’s lifetime, with an area of about 2000 square metres collapsing.”

During perihelion passage the southern hemisphere of the comet was subjected to high solar input, resulting in increased levels of activity and more intensive erosion than elsewhere on the comet.

“Inspection of before and after images allow us to ascertain that the cliff was intact until at least May 2015, for when we still have high enough resolution images in that region to see it,” added Mr Driver, who is working with Dr El-Maarry to investigate Rosetta’s vast image archive.

Looking in detail at the debris around the collapsed region suggests that other large erosion events have happened here in the past. El-Maarry and Driver found that the debris includes blocks of variable size ranging up to tens of metres.

“This variability in the size distribution of the fallen debris suggests either differences in the strength of the comet’s layered materials, and/or varying mechanisms of cliff collapse,” added Dr El-Maarry.

Studying comet changes like these not only gives insight into the dynamic nature of these small bodies on short timescales, but the larger scale cliff collapses provide unique views into the internal structure of the comet, helping to piece together the comet’s evolution over longer timescales.

“Rosetta’s datasets continue to surprise us, and it’s wonderful the next generation of students are already making exciting discoveries,” added Matt Taylor, ESA’s Rosetta project scientist.

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