It is the largest impact crater on the planet Mars. Located in the planet's southern hemisphere, the Hellas Basin is a gargantuan depression some 1,240 miles wide (2,000 km) and 4.4 miles (7 km) deep. In telescope views, like this Hubble Space Telescope image, it appears as a circular feature (lower right). Its floor is covered with frost in the martian winter and the entire basin is so large and contained that it sometimes contains more air inside it than the surrounding Mars terrain.