sublimation at the surface is a plausible explanation. They also raised the question
about whether these features were being exhumed or whether they were being
created by current activity. El-Maarry et al. (2017b) showed that some of these
features appeared on the nucleus of 67P at some time during the perihelion passage.
The surface changes that occurred are seen in the pre- and post-perihelion images in
Fig. 2.94. Boulders near the features marked with the yellow arrows appear to have
been exhumed during the perihelion passage suggesting that material surrounding
Fig. 2.92 Quasi-circular depressions in Anubis (top; N20160614T010041718ID10F22) and Hapi
(bottom; N20150122T223400384ID10F22)
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2 The Nucleus