Making tracks

DESPITE being Earth's nearest neighbour, the Moon has been a lonely place for the past three decades. Space probes have voyaged to the outer solar system, rovers have landed on Mars and orbiting telescopes have discovered thousands of worlds around other stars. But until this decade nothing, robot or human, had landed on the Moon since August 9th 1976, when Luna 24, a probe belonging to the Soviet Union, set itself down in Mare Crisium, just north of the lunar equator. That changed on December 1...