The launch of the next Martian rover is nine months away and counting. Astrobiologists, atmospheric scientists and geologists already are rehearsing their parts. Many Mars explorers attended a 10-day summer camp last month to prepare them for working on the Red Planet. Three spacecraft head to Mars next year. A common element of all three missions is the search for water, which would indicate Mars could support life. Scientists through the ages have wondered whether anything ever lived on Mars or ever could. In May, the first of NASA’s Mars Exploration Rovers is scheduled to launch from Cape Canaveral Air Force Station. A month later, a twin rover will follow. If successful, the missions will be the first to land safely on the surface since the Jet Propulsion Laboratory’s 1997 triumph, Pathfinder.