A study of clays suggests they might have been formed in hot magma rich in water — too hot to support microbial life. A Caltech planetary geologist is coauthor.
A standing theory about water on Mars is linked to blueberry-shaped formations in the Martian soil, such as this one in an image captured by the rover Opportunity and released in 2004. An alternate theory published Sunday in the journal Nature Geoscience argues, however, that Martian water's source water would have been far too hot to support microbial life. (NASA/JPL/U.S. Geological Survey/AFP/Getty Images)
In 2008, NASA's Phoenix Mars lander landed in the Martian arctic region and uncovered evidence for water ice.
A new study presents an alternative explanation for the prevalence of Mars' ancient clay minerals, which on Earth most often result from water chemically reacting with rock over long periods of time. The process is believed to be a starting point for life.
The clays, also known as phyllosilocates, are among the strongest pieces of evidence for a Mars that once was warmer, wetter and much more like Earth than the cold, dry, acidic desert which appears today.
Data collected by orbiting spacecraft show Mars' clay minerals may instead trace their origin to water-rich volcanic magma, similar to how clays formed on the Mururoa atoll in French Polynesia and in the Parana basin in Brazil. That process doesn't need standing bodies of liquid water.
Alain Meunier of France's Universite de Poitiers and a team studied clay minerals at Mururoa atoll in French Polynesia that seem similar to martian examples, and showed they were formed from precipitation of lava.
The same process has also occurred at other locations on Earth, including the Parana basin in Brazil, said the study in Nature Geoscience.
"To crystallise, clays need water but not necessarily liquid water. In other words, clays are not exclusively typical of soils or altered rocks; they may crystallise also directly from magmas," Meunier told AFP by email.
"Magmatic clays have no climatic significance. Consequently, they cannot be used to prove that the planet was habitable or not during its early history."
If the theory is correct, it "would imply that early Mars may not have been as habitable as previously thought at the time when Earth's life was taking hold," University of Colorado geologist Brian Hynek wrote in a comment.
Hynek said only on-the-spot examination of Mars' clay minerals can provide conclusive proof of their origin.
Two rovers that humans have placed on Mars, Opportunity which landed in 2004 and Curiosity earlier this year, may contribute such evidence.
The team says cooling lava can account for the most geographically abundant Noachian clay minerals. But that doesn’t mean water didn’t flow on the surface during brief episodes, as evidenced by the planet’s ancient river valleys, says coauthor Alain Meunier of the University of Poitiers in France.
Ehlmann says scientists need to find a spot on Mars where Nochian-aged clay is found so that all three proposed clay-forming mechanisms can be tested. Unfortunately, NASA’s Curiosity is not a good test location because the clays there are slightly younger and are clearly part of a sedimentary rather than volcanic deposit.