Vesta, the protoplanet Dawn has been studying for the past year or so, is full of surprises, one being how it manages to look so young despite its venerable age.
Scientists looking at data retrieved by the Dawn probe found that their expectations of what Vesta was supposed to be like were wrong, as is so often the case in this fast-changing field.
Astronomers have known that solar system bodies, like moons or asteroids undergo a weathering process.
This space weathering, as it's called, is the result of micrometeorites constantly pounding the surface as well as the unrelenting solar wind.
This is what happens on the Moon, meteorite impacts stir the lunar soil and spread it around. This fresh soil is always brighter than its surroundings and most of the Moon's surface.
Scientists have found that the top layer of soil darkens over time, partly due to material from meteorites that vaporize as they hit or as they're about to hit the surface, partly due to the effects of energetic, charged particles from the sun. In time, a dark, metallic layer of iron is formed.
Astronomers believed they would see the same thing on Vesta. And indeed, Vesta is affected by space weathering, but in an entirely different way. Two papers describing this have been published in Nature.
Recent meteorite impacts aren't surrounded by material brighter than the rest, rather, these bright spots are covered up very fast.
Scientists have a few theories to explain this, they believe that Vesta's steep topography generates constant landslides that cover up impacts and stir the top soil, mixing it.
But they also found that overall, the soil is not as dark as they expected, the metalling layer never forms. While there are a few dark patches, these are seemingly randomly distributed and seem to be the carbonized leftovers of meteorites.
As for why the soil doesn't darken, two explanations could be that meteorites don't vaporize as much when hitting the protoplanet and that the solar wind is too weak that far out for the phenomenon to occur.