Martian Meteorites Could Reveal That the Red Planet Was Wetter Than We Thought
Researchers simulated conditions that occur when a piece of the planet is ejected into space, and their findings could alter assumptions about the water budget of Mars.
In a twist for Martian meteorite studies, it turns out their mineral composition may show that the Red Planet was wet and possibly habitable in the past. It's the opposite of what researchers thought based on past examinations of meteorites, which hinted at a dry and dusty history.
The findings come from studying a synthetic version of whitlockite, a rare mineral on Earth. The research team ran shock-compression experiments to simulate the conditions that happen when a Martian sample is ejected from Mars into space; a fraction of these meteorites then make their way to Earth, where they fall on the surface and are collected.
Scientists studied the sample using X-ray experiments at Berkeley Lab's Advanced Light Source and at Argonne National Laboratory's Advanced Photon Source. Results show that the whitlockite becomes dehydrated and creates a mineral called merrillite, which has been found many times in Martian meteorites.
"If even a part of merrillite had been whitlockite before, it changes the water budget of Mars dramatically," Oliver Tschauner, co-leader of the study and a research professor in the Department of Geoscience at the University of Nevada, Las Vegas, said in a statement.
If the study proves true of actual Martian meteorites, this would help resolve a discrepancy between meteorite studies and examinations on the planet itself. While meteorite studies showed that Mars was dry, examinations by Martian rovers show abundant evidence of water. Certain minerals (such as hematite) formed in the presence of water. The Curiosity rover has also seen rounded pebbles and other evidence of ancient streambeds.
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.