Question: How do you find out where rocks come from? And doesn't cutting the rocks in half damage them or affect you results?

Thomas Barrett answered on 18 Mar 2015:

Well for most meteorites we don’t know where they come from. We can group them based on what they are made up of. In particular the isotopes of oxygen (16O 17O 18O) are really useful for showing us things that are linked to each other.

For the Moon and Mars we have a good idea of what the meteorite needs to be made up of, so if it has these things and a similar oxygen isotope signature then we know where it is from.

There is only one group of metoerites other than the martian and lunar samples that we know where they come from. They are called HEDs (HED stands for Howardite-Eucrite-Diogenite) and these are the things I look at in particular. We know these come from a large asteroid called Vesta in the main asteroid belt. We know this because telescope observations of Vesta have show a particular feature which we also saw in the lab for the HEDs. We then sent the Dawn spacecraft to check out Vesta and that has given us strong evidence they are from there.

Cutting a rock in half does damage it (you’re cutting it in two after all 😛 ) but it wont affect the chemisty of the rock. If you cut pencil in half its still a pencil 😛