Mars is known as the Red Planet. It is the fourth planet from the Sun and the only planet where humans have landed rovers. From the biggest volcano in the solar system to ancient riverbeds, learn why scientists are so interested in the Red Planet. Dr. Bruce Betts is Chief Scientist and LightSail Program Manager for The Planetary Society, the world's largest space interest group. Dr. Betts is a planetary scientist who earned a B.S. in physics and math and an M.S. in Applied Physics from Stanford and a Ph.D. in Planetary Science with a minor in Geology from Caltech. He spent several years with San Juan Institute/Planetary Science Institute as a Research Scientist, and later Senior Research Scientist. Dr. Betts is the author of Astronomy for Kids: How to Explore Outer Space with Binoculars, a Telescope, or Just Your Eyes! He regularly writes for The Planetary Society member magazine The Planetary Report , and on his blog on planetary.org.