The oldest craters on Mars are much more eroded and filled by younger deposits than are craters on the airless moon and Mercury. In some cases, wind has eroded the flat floor deposits in these Martian craters, exposing older layers beneath the surface. By determining what kinds of sediments or lavas fill these crater floors, we can learn more about what kinds of geologic processes shaped the surface of Mars.
To answer this question, we study the geologic context, stratigraphy, and composition of the crater-filling layered rocks. Context includes whether the crater formed on an older ridge in the landscape, where no water flowed into it from outside, or along a valley bottom, where a river drained into it and deposited sediments. Studying stratigraphy is like reading pages in a history book, with the oldest pages on the bottom, and the youngest on top. Changes from one layer to the next record changes in the environment and sediment sources through time. Using orbital instruments like the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the robotic Mars Reconnaissance Orbiter, we can interpret the composition of the layers, including whether they contain volcanic, clay, or sulfur-bearing minerals. This project is a collaboration between the Smithsonian, the Planetary Science Institute, and Georgia Tech.
Figure: (a) A 52-km crater in Noachis Terra, Mars, with bright- and dark-toned outcrops exposed on its floor. (b) Enlargement of an area on the southern side of the crater, showing dark-toned inverted paleochannels with lighter-toned outcrops beneath them.