Mars today is cold and dry and liquid water is not stable at the surface. There are several landforms that suggest the climate on Mars was once warmer and wetter - similar to Earth. Scientists have been intrigued by the discovery of layered deposits on Mars since they were recognized by Mariner 9 and Viking orbiters in the 1970s. Many of the layered deposits on Mars are light-toned, occur in crater interiors, and are characterized by thick, laterally continuous, repetitive sequences. There are many ways in which layered deposits can form on Mars, including volcanic, wind or water-related processes. The physical and chemical nature of the light-toned layered deposits in Terby crater and other craters around the great Hellas impact basin are consistent with deposition of material in a large, standing body of water much earlier in Mars' history.