A view of Mars as it might have appeared more than 2 billion years ago, with a low-latitude ocean filling the lowland basin that now occupies the north polar region. Topographic deformation of features that ring the basin, which are hypothesized to be shorelines formed by an ancient ocean, suggests that Mars experienced significant true polar wander--reorientation of the planet relative to its rotation axis--that brought the planet into its present rotational state. The margins of the ocean shown here account for the topographic deformation that would have resulted from this reorientation. Sinuous features near the top of the image are valleys carved by large floods that may have supplied the ocean water. The image was generated using Viking Orbiter images and topographic data from the Mars Orbiter Laser Altimeter on board the Mars Global Surveyor spacecraft. (Taylor Perron/UC Berkeley