Martian clays may have formed from water-rich lava flows, reports a study published online this week in Nature Geoscience. The findings challenge the suggestion that these clays provide evidence for a warm, wet climate on early Mars.

Alain Meunier and colleagues analysed the spectral characteristics of clay minerals formed directly from water-rich lavas in French Polynesia. They show that the spectral characteristics of the clays are similar to those of martian clays, as measured by the Mars Reconnaissance Orbiter. The findings suggest that the martian clays may have formed from water-rich volcanic lavas, rather than from the weathering of surface rocks by liquid water, as previously assumed. Further evidence for a magmatic origin comes from the association of martian clays with lava flows on the surface of Mars, and the chemical composition of clay minerals in martian meteorites found on Earth.

In an accompanying News and Views article, Brian Hynek writes that “such a result would imply that early Mars may not have been as habitable as previously thought at the time when Earth’s life was taking hold.”