After a seven-month epic voyage across interplanetary space, NASA’s two exploration rovers are on final approach to Mars. Spirit takes the first plunge into the Martian atmosphere tonight while its twin, Opportunity, begins its perilous decent Jan. 25. With any luck, things will go more smoothly for NASA than they have for the troubled British Mars probe, the Beagle 2. For readers inspired to make their own, armchair journeys to the Red Planet, here’s a guide to essential titles, most published within the past year: