Space weathering

The constant flux of high energy particles and micrometeorites, along with larger meteorites, act to comminute, melt, sputter and vaporize components of the lunar soil.

These are created when micrometeorites melt a small amount of material, which incorporates surrounding glass and mineral fragments into a glass-welded aggregate ranging in size from a few micrometers to a few millimeters.

Space weathering also produces surface-correlated products on individual soil grains, such as glass splashes; implanted hydrogen, helium and other gases; solar flare tracks; and accreted components, including nanophase iron.

On the Moon, the spectral effects of space weathering are threefold: as the lunar surface matures it becomes darker (the albedo is reduced), redder (reflectance increases with increasing wavelength), and the depth of its diagnostic absorption bands are reduced[4] These effects are largely due to the presence of nanophase iron in both the agglutinates and in the accreted rims on individual grains.

Evidence from NEAR Shoemaker's x-ray measurements of Eros indicate an ordinary chondrite composition despite a red-sloped, S-type spectrum, again suggesting that some process has altered the optical properties of the surface.

Because Itokawa is so small (550 m diameter), it was thought that the low gravity would not allow for the development of a mature regolith, however, preliminary examination of the returned samples reveals the presence of nanophase iron and other space weathering effects on several grains.

[8] There is evidence to suggest most of the color change due to weathering occurs rapidly, in the first hundred thousands years, limiting the usefulness of spectral measurement for determining the age of asteroids.

For one thing, it is significantly hotter in the day (diurnal surface temperature ~100 °C for the Moon, ~425 °C on Mercury) and colder at night, which may alter the products of space weathering.

In addition, because of its location in the Solar System, Mercury is subjected to a slightly larger flux of micrometeorites that impact at much higher velocities than the Moon.