The colorful walls of an exposed impact crater on Mars

Impact craters have been called the "poor geologists' drill," since they allow scientists to look beneath to the subsurface of a planet without actually digging down. It's estimated that Mars has over 600,000 craters, so there's plenty of opportunity to peer into the red planet's strata--especially with the incredible HiRISE (High Resolution Imaging Science Experiment) camera aboard the Mars Reconnaissance Orbiter, which has been orbiting and studying Mars from above since 2006.