Billions of years ago, Mars had flowing water, but the amount of water and how quickly it disappeared is a great source of debate among scientists. Proponents of a drier Mars will now have to consider that one of their key pieces of evidence might actually suggest the opposite.
In a new study, published in Nature Communications, researchers have uncovered evidence that a common water-free Martian meteorite mineral, merrillite, can form from the dehydration of another mineral, whitlockite, after an intense shock, such as the one that ripped these rocks from the Red Planet.
Both whitlockite and merrillite are rare on Earth, but their relationship with H2O is crucial in order to investigate how much water was present on ancient Mars and if the water was from Mars itself or brought forth by comets and asteroids.
The researchers shocked whitlockite with the same intensity of a real meteorite impact, although for only about 100-billionths of a second, between one-tenth and one-hundredth of an actual meteor impact. Under these conditions, 36 percent of whitlockite was turned into merrillite.
“If even a part of merrillite had been whitlockite before, it changes the water budget of Mars dramatically,” co-lead author Professor Oliver Tschauner, from University of Nevada, Las Vegas, said in a statement.
The study is one of the first to research shock effects on synthetic whitlockite, although what's dehydrating the mineral is probably the heat from the shock rather than the pressure. The team had to shoot the whitlockite at about 750 meters per seconds (1,678 mph), which created a pressure 363,000 times greater than the air in a basketball.
“You need a very severe impact to accelerate material fast enough to escape the gravitational pull of Mars,” Tschauner added.
While the research certainly challenges the idea that merrillite is clear evidence that Mars was on the dry side, it doesn't mean that Mars was a water world.
“The only missing link now is to prove that (merrillite) had, in fact, really been Martian whitlockite before,” Tschauner continued. “We have to go back to the real meteorites and see if there had been traces of water.”
The team is planning to investigate in greater detail Martian meteorites in light of the recent findings. Of course, as they state, the best approach would be the direct analysis of rocks from Mars itself.