Substantial quantities of liquid water must have been stably present in the early history of Mars. The findings of OMEGA, on board ESA’s Mars Express, have implications on the climatic history of the planet and the question of its ‘habitability’ at some point in its history. These conclusions were drawn thanks to data on Martian surface minerals obtained by OMEGA (Observatoire pour la Mineralogy, l’Eau, les Glaces et l’Activit