From orbit, pictures have shown ancient gullies that were likely worn down by water flow, although other explanations, such as lava, have been proposed as well. In 2015, NASA announced, based on examinations by the Mars Reconnaissance Orbiter, that briny water may even flow today. Features called recurring slope lineae on Mars, which tend to appear in warmer weather, appear consistent with water flow.
Whitlockite contains phosphorous - a needed element for life on Earth - and can also dissolve in water. Since merrillite is found in so many Martian meteorites, the study suggests that habitable conditions for life on Mars were common, at least in the region from where the meteorites came.
"The only missing link now is to prove that (merrillite) had, in fact, really been Martian whitlockite before," Tschauner said. "We have to go back to the real meteorites and see if there had been traces of water."
A key limitation of the study is the origins of Martian meteorites. Many collected on Earth likely came from one region of Mars, and only during a narrow time period: 150-586 million years ago. These meteorites represent samples below the surface that were excavated when an impact on Mars sent them flying off the planet. Because these samples were buried, they are believed to indicate the Martian environment in the more ancient past.
The researchers plan follow-up studies with actual Martian meteorite samples later this year. Independent studies are ongoing to learn more about the past habitability of Mars. NASA plans to send another rover there in 2020 to collect samples and possibly cache them for a future sample-return mission. Such a sample could then be examined on Earth with sophisticated laboratory instruments that are impossible to send to Mars due to their size, among other factors.
The research was published in Nature Communications.
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