At one point in its history, conditions on Mars allowed liquid water—and potentially life—to exist on its surface. Today, however, the temperature and atmospheric conditions on Mars make liquid water unstable. Martian meteorites, formed and altered in the presence of crustal fluids, can tell us something about the composition, origins, and history of sedimentary materials on Mars. A recent study led by Jessica Barnes from the University of Arizona and colleagues analyzed the hydrogen isotopic composition of the Martian meteorites Northwest Africa 7034 (also known as Black Beauty) and Allan Hills 84001. Hydrogen isotopes can inform us of different sources of water due to the fractionation between the lighter isotope (1H, hydrogen) and the heavier isotope (2H or D, deuterium). Their results show that when Mars supported liquid water, this water was derived from at least two distinct sources in the Martian mantle. This heterogeneity implies that the Martian mantle did not experience large-scale mixing during accretion and differentiation, which calls into question the “canonical” model of differentiation of Mars via a global magma ocean. READ MORE