Re: get those rocks back to our home world.
The trouble is in order to get (eg) 1kg of samples back to Earth, you need a craft capable of returning to Earth from Mars (never been done). It'll probably also have to carry enough fuel to brake into Earth orbit, rather than parachute down and potentially break quarantine. Plus you need something that can take the samples from the surface of Mars and into orbit, probably to somehow automatically dock with the return craft in Mars orbit (again, never been done that far from Earth).
The biggest issue though is that both of these craft have to be carried all the way to Mars, and the orbital rocket has to be safely landed, and all of this takes a massive amount of fuel.
Then you add on the fun little problems, like building a rocket engine that can survive the months long trip to Mars, the landing, and also survive several days on Mars, and can still ignite successfully and reach orbit. Exactly what kind of fuel do you use that doesn't need heating or cooling or compressing for that long, whilst still being as efficient as possible?
All in all it's a tricky set of problems, and will probably cost a lot of money to do.
For more info, here's a look at a NASA plan for sample return from thirty years ago, which goes through some of the problems (eg taking a parachute all the way from Earth, to Mars and back again was too much mass, so they designed the return capsule to just crash).
Biting the hand that feeds IT
