This picture, taken recently by America's Mars rover Opportunity, shows its tracks on the planet's surface. The objects in the foreground are not signs of Martian agriculture, but parts of the rover itself. Opportunity is one of two rovers that landed in 2004. Its sister vehicle, Spirit, gave up the ghost in 2010, but Opportunity rolls on. It passed 3,000 Martian days of service (each 37 minutes longer than a terrestrial one) on July 2nd. On August 6th, if all goes to plan, a third rover, Curiosity, will arrive on Mars as well.