Few features on any planet loom as large — in telescopes or in the minds of scientists — as the huge scar on Mars known as Valles Marineris. To call the apparent drainage system a series of valleys is like calling the Grand Canyon a gully. And to claim you know just how it came to exist is a recipe for much scientific wrangling. We simply don’t know a lot about Mars’ past. Nor its present. Even after many spacecraft landings on Mars and hundreds of thousands of satellite pictures, there is no good ground-level snapshot showing what Valles Marineris looks like today. Now an artist has offered several views of the region, its deep canyons and towering cliffs, all based on topographical data obtained by the Mars Orbiter Laser Altimeter (MOLA) instrument on NASA’s Mars Global Surveyor spacecraft.