re: In situ
It makes a lot of sense to study rocks on the spot:
1) it remains in its original environment
2) it doesn't go through space for months (if not years) to get to Earth.
3) it doesn't get contaminated by Earth's environment if the laboratory itself is clean.
4) it's a lot less expensive and takes much less time.
5) technological progress makes this concept a lot more credible (see the difference between the Surveyors on the Moon and the Vikings on Mars).
Raoul