Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2002 October 1 Rectangular Ridges on Mars Credit: Malin Space Science Systems, MGS, JPL, NASA Explanation: What could cause rectangular ridges on Mars? As data flows in from the two spacecraft currently orbiting Mars, surface structures are seen that are not immediately understood. These structures pose puzzles that planetary geologists are eager to solve, as they might provide clues to past processes that have shaped Mars over billions...