Clays found in the southern hemisphere of Mars are often considered to be proof of liquid water on the red planet 4.5 to 4 billion years ago. But the work of a Franco-American team, led by researchers at the Université de Poitiers, questions this interpretation. In an article published online in the journal Nature Geoscience, they show that these clays are likely to be of magmatic origin. This work could have implications for the search for life signs on Mars.

The clays, rich in iron and magnesium, were thought to be the remnants of rocks warn down liquid water. This left scientists believing that water was present on the Martian surface during this early period. However, researchers have recently shown that magma probably formed these clays. To support their hypothesis, the researchers examined the basalts of the Mururoa Atoll (French Polynesia). These basalts contain ferro-magnesian clays similar to those found on Mars.

The researchers showed that these clays were formed from residual magmatic liquids rich in water. The formation of these clays does not require the presence of liquid water. In addition, scientists have also shown that the infrared spectra of Martian clays — measured by the orbiter Mars Express and Mars Reconnaissance Orbiter — are identical to that of clays Mururoa.

If there were a presence of liquid water around 3 billion years ago, proven by traces of rivers, lakes and alluvial fans, nothing suggests that there may have been water 4.5 or 4.0 billion years ago, as previously believed. The time period for the emergence of life on Mars could have been much shorter than expected. The Curiosity mission that will explore Mars Gale Crater — part of the sedimentary formations which indicate the presence of liquid water at a much later period — is expected to raise a number of questions.