Mars being once coated with life - now that’s a theme already long ago turned into a sci-fi cliché. And now, it looks like it’s less and less a matter of fiction, as science recently took another step closer to proving that Mars was another Earth, a long time ago (but not in a galaxy far, far away).

If life had indeed existed on the Red Planet, then scientists should have found traces of carbonate on its surface. Which they hadn’t, until now. NASA’s Mars Reconnaissance Orbiter made us one hell of a Christmas present: images clearly showing pretty large (10 sq. km) Martian patches of terrain covered with magnesium carbonate. According to National Geographic, these areas are located in the Nili Fossae region, where the surface has been exposed to a more or less life-friendly atmosphere for no less than 3.6 billion years.

Why is this finding so important? Because carbonate minerals can’t form without water. No wonder our planet has lots of the stuff lying around (limestone and chalk are some of the more non-exotic examples). But Mars had seemed devoid of any major concentrations of this type of mineral; only small percentages had been previously found by the Mars Phoenix Lander in arctic soils.

The presence of water on Mars had already been largely agreed upon; but the general belief was that Martian water was too acidic for even the most resilient or stubborn of life forms. “So the fact that … carbonate is still present means that the waters flowing through [Nili Fossae] must not have been acid,” said professor Bethany Ehlmann from the Brown University, who led the research.