Mawrth Vallis is an ancient Mars river channel (~15km wide) located along the crustal dichotomy boundary that exposes abundant light-toned layers of clay-rich rocks. Indicative of aqueous alteration, these clays may have been deposited during massive flooding events or in a shallow lake environment, but also could have been caused by in-place weathering of preexisting layered material like volcanic ash or crater ejecta. Clay minerals (or phyllosilicates) are good at preserving evidence of past life and habitable conditions, and so this area has been intensely studied as a candidate landing site for several robotic missions. The colors in the image above show the presence of aluminum phyllosilicates in blue-purple tones, Fe/Mg phyllosilicates in green-yellow, and hydrated minerals red tones.
The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is one of six science instruments on NASA's Mars Reconnaissance Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory, the CRISM team includes expertise from universities, government agencies and small businesses in the United States and abroad.
CRISM's mission: Find the spectral fingerprints of aqueous and hydrothermal deposits and map the geology, composition and stratigraphy of surface features. The instrument also tracks seasonal variations in dust and ice aerosols in the Martian atmosphere, and water content in surface materials — leading to new understanding of the climate.