ARES VALLIS, Mars: Great truth often is found in the tiniest and most ordinary of details. If so, a blizzard of revelations may be raining down now that the Sojourner rover has rolled carefully down the Pathfinder ramp and begun poking around the Martian surface. On Monday, the rover, which looks more like a post-modern plant stand than a space vehicle, spent ten hours studying a nondescript rock dubbed "Barnacle Bill" by scientists, in order to determine its composition. A neighboring rock nicknamed "Yogi" is next. Once Sojourner receives the steering signals broadcast by NASA late Monday, the scrappy little craft will amble over to the new rock at a speedy clip of one centimeter per second, studying soil characteristics along the way. NASA has yet to release any detailed information from Sojourner's chemical analyses, beyond a few hints about indications of past life on the Red Planet. But the agency is releasing a stream of striking panoramic shots taken by the rover and Pathfinder that provide convincing evidence that the planet was inundated by ancient floods, some the size of the massive deluge that filled the Mediterranean basin. Today's Martian forecast: dry, with a temperature at dawn of minus 76 degrees Fahrenheit.