They may not look like it, but each of these photos from Rosetta is of the same site on Comet 67P/ Churyumov-Gerasimenko, within just six short weeks. Something big is happening up there—but what is it?

This particular comet site has been steadily monitored by the ESA since August of 2014, and nothing has been happening. Literally. Viewed in detail of up to 1/10 of a meter, the site had stayed exactly the same. Until late May, when suddenly everything started changing again and again and again.


Some land features disappeared, others were added. Some were temporary, some stayed. What’s happening there and why? Scientists still aren’t sure, but they’ve come up with a few theories:

A simple possibility is that the surface material is very weak, allowing for more rapid erosion, but it is also possible that the crystallisation of amorphous ice or the destabilisation of so-called ‘clathrates’ (a lattice of one kind of molecule containing other molecules) could liberate energy and thus drive the expansion of the features at faster speeds.

A settled explanation for the rapid changes, though—and when or if they will stop—remains to be seen.

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