Mars may be as close to Earth as it’s been in 60,000 years, but for space exploration advocates who’ve been pining to follow up the Apollo moon missions with a human expedition to Mars, the Red Planet has never been more distant. “Right now, a Mars mission is on no one’s radar scope,” said Karl Leib, a political scientist at Wabash College, Ind., and co-author of a book on space policy. “What matters now is just getting the shuttle back into service and getting NASA back to the point where it can trust itself.”