Martian rock 'White Boat'. This rock (centre) was examined by the Mars Exploration Rover Spirit on 9 February 2004. Spirit drove here after leaving the Adirondack rock. White Boat was examined because its light colour and more tabular shape made it stand out from the surrounding rocks. The next day, Spirit continued its exploration of the rocks in the Gusev Crater, where it landed on 4 January 2004. Spirit, and an identical rover called Opportunity, are exploring the Martian surface and looking for evidence of water on Mars.