What are we hoping to learn from the abrasion patches?

A great deal.

• What is the overall elemental chemistry of the rock/target? (identifying iron, carbon, sulfur, magnesium, oxygen etc. etc.)
• How are the elements in the rock put together? (in other words, the minerals formed by those elements)
• Are there organic molecules present? (If so, not necessarily signs of biology, but are always worth learning more about)
• The “texture” of the rock (is it made of loosely bound material like pebbles and sand, or large close-packed solid mineral grains, or something else entirely?)
• What is the rock like inside? (Sometimes different from the outside! Percy has found dissolved salts and mineral veins in some rock interiors, which were not even hinted at from analysis of the outer surface)

The above is not a complete list. The dust and weathering rinds Paul Hammond mentions (the undisturbed outer surface of the rock), in general, prevent you from answering these questions in the same detail, or at all. By answering the first two questions above, you get a good idea of how the rock formed and what it contains (e.g. is this volcanic rock - like from a lava flow - or something laid down in calm water, or something else entirely)?

Generally speaking, if the mission decides to abrade a hole in some rock, it’s a sign that the geologists find the stuff interesting, or at least need to identify what’s at that spot to make sense of the immediately surrounding landscape.

I’m still working on a series of posts explaining all this in more detail - with neat pictures - but it’s going to take a while yet (we’ve made more than 30 of these holes, and they’ve shown us quite a few different things from start to finish!) Questions are welcome!