Clay minerals on Mars could have formed during the creation of the Martian crust itself, long before any water flowed on the planet, suggests new research that could rewrite the early history of the Red Planet.
"One of the complications that comes up in Mars evolution is that we can't create a scenario where surface weathering had the capacity to produce the extent of mineral alteration that we see," said Jack Mustard, Professor at Brown University in the US and study co-author.
Scientists have found evidence of ancient phyllosilicates, or clays, on the Martian surface.
Phyllosilicates are generally formed by the interaction of water with volcanic rock, leading many scientists to conclude that there must have been sustained surface water, groundwater or active hydrothermal systems at some point in Martian history.
But the new scenario, presented in the journal Nature, offers a means of creating widespread clay deposits that does not require a warm and wet climate or a sustained hydrothermal system on early Mars.
Backed by lab experiments and computer models, the researchers laid out how the scenario would have worked.
In the very early solar system, Mars and other rocky planets are thought to have been covered by oceans of molten magma.
As the Mars magma ocean began to cool and solidify, water and other dissolved volatiles would be outgassed to the surface, forming a thick, steamy atmosphere surrounding the planet.
The moisture and heat from that high-pressure steam bath would have converted vast swathes of the newly solidified surface to clay.
As the planet then evolved over billions of years, volcanic activity and asteroid bombardments would have covered the clays in some places and excavated them in others, leading to the widespread but patchy distribution seen on the surface today.
To demonstrate that the mechanism they propose is plausible, the researchers synthesized rock samples matching the composition of Martian basalt.
They then used a high-pressure device to recreate temperature and pressure conditions that may have been present amid the steam atmosphere created by a magma ocean.
After cooking samples for two weeks, the team checked to see if they had been altered and to what extent.
"It was really remarkable how quickly and extensively this basalt was altered," said lead researcher Kevin Cannon, a postdoctoral researcher at the University of Central Florida.
The steam atmosphere associated with a magma ocean could have survived for as long as 10 million years or more, the researchers said.
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