Mercury is getting bombarded by meteorites, much more so than our own Moon. 

Scientists used images taken by the Messenger spacecraft to examine the surface to try and understand why there are so few large boulders. Here’s the funny part of the story: they wanted to compare the images from Messenger with images taken of the Moon by the Lunar Reconnaissance Orbiter (LRO). Now, Messenger’s images can resolve boulders at about five meters in diameter or larger. The LRO, on the other hand, has a way higher resolution, so the team had to “deteriorate” the LRO images to match the quality of the Messenger images. 

Not surprisingly, Mercury receives over fifty times the micrometeoroid flow that the Moon gets, as a result of being closer to the Sun, whose gravity pulls everything in and hits Mercury. The particles are even coming in at a faster rate thanks to the Sun’s immense gravity, and those particles are beating up the boulders on the surface like sandpaper on wood, wearing them down far more quickly than the rocks on the Moon are worn down. Plus, the huge amount of particle flow has also led to a thicker regolith layer on Mercury, which means larger meteors are not displacing rocks and creating big boulders to start with. So Mercury has fewer boulders compared to the Moon because it starts with fewer and they’re worn down more quickly. This work is published in the journal Icarus.

More Information

Ural Federal University press release

“Boulders on Mercury,” Mikhail A. Kreslavsky, Anastasia Yu. Zharkova, James W. Head, and Maria I. Gritsevich, 2021 July 20, Icarus