What lies beneath the Opportunity rover? Much of the plains of Meridiani Planum as seen by the Opportunity rover are flat, featureless, and covered by sand dunes.  In May 2005, while the Mars Express spacecraft orbited high above, the Opportunity rover on route to Endurance crater and driving through “Purgatoy Dune” got stuck in the deep sand for more than a month. The MARSIS radar sounder has probed deep below the surface of Meridiani Planum revealing deposits of windblown sand are as much as 1,000 meters (about 3,280 feet) thick in some areas.