The US space agency is celebrating as its robot rovers Spirit and Opportunity reach their second year of science operations on the surface of Mars.
First to land was Spirit, which touched down in the rocky basin of Gusev Crater at 0435 GMT on 4 January 2004. pportunity landed on 25 January, rolling into a small crater punched in the dark plains of Meridiani Planum, on the other side of the Red Planet. The golf cart-sized vehicles were only supposed to survive for three months. The missions are amongst Nasa's biggest successes of recent years. Both rovers succeeded in their main assignments: finding geological evidence that water once flowed on Mars.
