22 March 2017
Comet 67P: a large landslide on another world
In a paper published in the journal Nature Astronomy (Pajola et al. 2017), Maurizio Pajola and a cost of dozens have recorded a large rockfall event occurring on Comet 67P / Churyumov-Gerasimenko. This event was recorded by the European Space Agency’s Rosetta mission over the period between 2014 and 2015.
The event started when, in September 2014, the team spotted a large (70 m long) fracture at the top of a cliff now known as Aswan:-
Pajola et al. (2017) report that on 10th July 2015 Rosetta captured a large plume of dust emanating from this area; and on 15th July 2015 a new image of Comet 67P showed that the rock slope had collapsed.
The volume of the rockfall is estimated to have been about 22,000 cubic metres, from a cliff that is 134 metres high. Before and after images of the rockfall site reveal an arcuate scar and a boulder field below:
Pajola et al. (2017) suggest that that collapse was driven by thermal changes in the rock mass, which is considered to be deeply fractured, as Comet 67P moved closer to the sun. However, the actual failure occurred at night, when the calculated thermal gradients were low. I wonder therefore if this is the first time that progressive failure has been observed on another body in the solar system?
In astronomical terms, the main interest here is that the rockfall mechanism provides an explanation for the outbursts of dust that have been observed to issue from the surface of Comet 67P.
Pajola, M. et al. 2017. The pristine interior of comet 67P revealed by the combined Aswan outburst and cliff collapse. Nature Astrononmy 1, 0092 (2017).