Imagine orbiting this one (Image: NASA/JPL) Which space rock?

DECIDING to send astronauts to an asteroid is all very well, but now NASA will have to find the few space rocks that are suitable to visit, and work out how to rendezvous safely.

Last month, US president Barack Obama announced the next destination for NASA astronauts would be an asteroid, as early as 2025. The goal would be to gain experience of safely sending humans far from Earth, as a stepping stone towards longer journeys to Mars. Studying the interior of an asteroid up close could also prove important if …