Somewhat depends on what they find, and if they're able to usefully exploit it. But for ambition, I'd say at least a 3. Of course, you could argue that anyone

Somewhat depends on what they find, and if they're able to usefully exploit it. But for ambition, I'd say at least a 3. Of course, you could argue that anyone who can return non-negligible amounts of mass to earth makes it to 4...