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Surface changes on comet 67P/Churyumov-Gerasimenko suggest a more active past

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Science  31 Mar 2017:
Vol. 355, Issue 6332, pp. 1392-1395
DOI: 10.1126/science.aak9384

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The changing surface of a comet

From 2014 to 2016, the Rosetta spacecraft investigated comet 67P/Churyumov-Gerasimenko as it passed through the inner solar system. El-Maarry et al. compared images of the surface taken before and after the comet's closest approach to the Sun. Numerous geological changes were evident, including cliff collapses, large boulders that moved, and cracks that opened up. These seem to have been triggered by seasonal factors, such as the amount of sunlight falling on each area. Understanding such changes should help elucidate comet formation and evolution.

Science, this issue p. 1392

Abstract

The Rosetta spacecraft spent ~2 years orbiting comet 67P/Churyumov-Gerasimenko, most of it at distances that allowed surface characterization and monitoring at submeter scales. From December 2014 to June 2016, numerous localized changes were observed, which we attribute to cometary-specific weathering, erosion, and transient events driven by exposure to sunlight and other processes. While the localized changes suggest compositional or physical heterogeneity, their scale has not resulted in substantial alterations to the comet’s landscape. This suggests that most of the major landforms were created early in the comet’s current orbital configuration. They may even date from earlier if the comet had a larger volatile inventory, particularly of CO or CO2 ices, or contained amorphous ice, which could have triggered activity at greater distances from the Sun.

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