A year after the landing of Mars Pathfinder, mission scientists say that data from the spacecraft paint two strikingly different pictures of the role of water on the red planet, and yield surprising conclusions about the composition of rocks at the landing site. Pathfinder data suggest that the planet may have been awash in water three billion to 4.5 billion years ago. The immediate vicinty of the Pathfinder landing site, however, appears to have been dry and unchanged for the past two billion years.