Mars Clay May Have Formed Far More Recently Than Once Thought

It turns out that there may be evidence for more recent clay formation on Mars, which may tell researchers a bit more about the Red Planet and show a bit more about the conditions that may have once been hospitable to Martian life.

Recent orbital and rover missions to Mars have turned up ample evidence of clays and other hydrated minerals formed when rocks are altered by the presence of water. Most of that alteration is thought to have happened during the earliest part of Martian history, more than 3.7 billion years ago. This latest study, though, shows that later alteration may be more common than once thought.

Most clay deposits on Mars have turned up in terrains that date back to the earliest Martian epoch, known as the Noachian period. Clays also tend to be found in and around large impact craters, where material from deep below the surface has been excavated. Scientists have generally assumed that the clays found at impact sites probably formed in the ancient Noachian, became buried over time, and then were brought back to the surface by the impact.

"Because central peaks contain rocks uplifted from depth, some previous studies have assumed the clays found within central peak regions are uplifted too," said Ralph Milliken, one of the researchers, in a news release. "What we wanted to do was look at lots of these craters in detail to see if that's actually correct."

The scientists performed a survey of 633 crater central peaks across Mars. Of these peaks, the researchers found that 265 of them had evidence of hydrated minerals, the majority of which were consistent with clays. In the end, they found that in about 65 percent of cases the clay minerals were associated with uplifted bedrock. This means that 35 percent were not associated with uplift.

Instead, they found the clays in impact melt, which are deposits of rock that had been melted by the heat of an impact and then re-solidified. This means that the clay minerals probably formed sometime after impact. In one case, the researchers found clays in fairly young craters, one just formed in the last 2 billion years.

"What this tells us is that the formation of clays isn't restricted to the most ancient time period on Mars," said Milliken. "You do apparently have a lot of local environments in these crater settings where you can still form clays, and it may have occurred more often than many people had thought."

The findings are published in the Journal of Geophysical Research: Planets.

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