The localised dots in the map show individual sites where hydrated minerals formed only in the presence of water were detected. More than ten different hydrous minerals have been found on Mars, with many occurrences found in the same site. In total, several thousand individual mineral exposures have been detected on Mars. The detections were made by combining observations made by ESA’s Mars Express OMEGA instrument and NASA’s Mars Reconnaissance Orbiter CRISM instrument.
The hydrated sites are found in various geological landscapes. Over 50% are associated with an impact structure – exposed in their crater walls, floors or central peaks – that have excavated older material from below. Sedimentary deposits and crustal outcrops account for a little under the remaining half of the occurrences, with ancient river deltas accommodating 5% of the sites.
They are primarily seen in the most ancient terrain dating back to over four billion years ago, suggesting that Mars may have sustained surface and subsurface liquid water for the first few hundred million years of its life, providing conditions favourable to life.