I'm personally interested in the biological implications of different isotope variations on biology. This can be tested on earth by separating them and just observing, but determining the isotope variations on other planets is what I'm not sure about.
I know the Curiosity rover can do a range of experiments and chemical analyses, but I'm not super familiar with them.
Can Curiosity test for isotope variations in martian soil?
If not, is there any other known way of testing for isotope variations, maybe through observation through a telescope (I really don't know), or possibly knowledge about the historical formation of the universe and solar system (I'm not an astronomer)?