David Blewett

The hollows are remarkable because they have a crisp, fresh appearance, they are probably younger than a few tens of millions of years, but some hollows are probably forming today. It is amazing to find ongoing geological activity modifying the surface of Mercury.

MESSENGER has been a fantastic mission that has given humans our first global look at one of Earth's closest relatives, mercury turned out to be stranger than anyone would have guessed. It looks roughly like the moon, but MESSENGER has shown that Mercury is vastly different from the moon in just about every way.

I am very lucky to have been part of the MESSENGER science team since before the first Mercury flyby, i was among the first humans to see the stark beauty of what was once 'Mercury incognito.' I have been working with a super team of scientists and engineers, and made good friends. It will be sad when the radio tracking tells us that the spacecraft made its final orbit, knowing that a tiny new impact crater has appeared on the surface.

Hollows are one of the surprises in terms of the geological processes that shape the surface at small scales.

It appears that there is something in the rocks that can't stand up to the punishing environment on Mercury's surface and, as a result, is lost in a sublimationlike process.

Based on the abundances that were measured, it seems likely that it is a sulfur compound that is being destroyed and lost to space in the locations where hollows are forming.