The BepiColombo spacecraft is a joint project of the Japanese and European space agencies. It swung by Mercury in the early hours of Oct. 2 and passed within a mere 200 kilometers (about 124 miles) in the early hours of October 2 2021. As designed, it took spectacular photographs of the surface at that time.
A Lobate Scarp:
BepiColombo captured the sun rising over “Astrolabe Rupes,” a striking lobate scarp on the surface.
A “lobate scarp” is a long, curved structure created when one part of a planet’s crust is pushed over another, as happens if a cooling planet contracts.
There are smaller lobate scarps on the Moon, but they occur on Mercury on a much larger scale, and the Astrolabe Rupes in particular is 250 kilometers long (155 miles).
Strange New Worlds:
One theory about the history of Mercury is that it may have begun as a larger body that was then stripped of most of its rock by a giant impact. This left it with a relatively large iron core, where its magnetic field is generated, and only a thin rocky outer shell. But that outer shell seems to have been the site of a lot of geological activity, not only the overlapping that might create lobate scarps but volcanic activity too.
Some questions for planetary astronomers now are: What are the volatile substances that turn violently into gas to power the volcanic explosions? How did Mercury retain these volatiles if most of its rock had been stripped away? How long did volcanic activity persist?