NASA's Spirit rover rolled 59 feet (17.7 meters) around the rim of a crater to begin inspecting firsthand a drift of windblown material that puzzles scientists.
Scientists sent the six-wheeled robot geologist to the dune, nicknamed "Serpent," to analyze its composition. They are unsure whether it is a pile of sand or dust.
NASA planned for Spirit to analyze the material Wednesday before driving over the dune to a site from which it can take panoramic pictures of the surrounding terrain.
Halfway around Mars, Spirit's twin rover, Opportunity, began to wrap up analysis of a rock outcrop at its landing site.
Opportunity was expected to scuff up the outcrop with one of its wheels Wednesday, allowing scientists to assess the rock's hardness. This week the rover should move out of the crater where it landed to study the plains of Meridiani Planum.
The space agency sent the two rovers to Mars on a $820 million mission to search for evidence the planet once was a wetter world. Opportunity already has found geologic clues that was the case.
