Mars Exploration Rover on the surface of Mars, artwork. The first of two identical NASA rovers, Spirit, landed on Mars on 4 January 2004. The second, Opportunity, landed on the other side of the planet on 24 January 2004. The rovers are powered by solar panels (flat, across centre) and are mobile. Cameras mounted on the mast give scientists panoramic views of the Martian surface. This enables them to instruct the rovers which rocks to analyse and where to look for water. Tools on board the golf buggy-sized rovers include spectrometers for analysing rock samples, a microscope and an abrasion tool. Each rover has a 90-day mission on the surface of Mars.