The fact that experiments showed even partial conversion to merrillite in these lab-created conditions, a longer duration impact would likely have produced “almost full conversion” to merrillite, Tschauner said.
He added that this latest study appears to be one of the first of its kind to detail the shock effects on synthetic whitlockite, which is rare on Earth.
Researchers blasted the synthetic whitlockite samples with metal plates fired from a gas-pressurized gun at speeds of up to about half a mile per second, or about 1,678 miles per hour, and at pressures of up to about 363,000 times greater than the air pressure in a basketball.
“You need a very severe impact to accelerate material fast enough to escape the gravitational pull of Mars,” Tschauner said.
At Berkeley Lab’s ALS, researchers used an X-ray beam to study the microscopic structure of shocked whitlockite samples in a technique known as X-ray diffraction. The technique allowed researchers to differentiate between merrillite and whitlockite in the shocked samples.
Separate X-ray experiments carried out at Argonne Lab’s APS showed that up to 36 percent of whitlockite was transformed to merrillite at the site of the metal plate’s impact with the mineral, and that shock-generated heating rather than compression may play the biggest role in whitlockite’s transformation into merrillite.
There is also evidence that liquid water flows on Mars today, though there has not yet been scientific proof that life has ever existed on Mars. In 2013, planetary scientists reported that darkish streaks that appear on Martian slopes are likely related to periodic flows of water resulting from changing temperatures. They based their analysis on data from NASA’s Mars Reconnaissance Orbiter.[xyz-ihs snippet=”Adsense-responsive”]And in November 2016, NASA scientists reported that a large underground body of water ice in one region of Mars contains the equivalent of all of the water in Lake Superior, the largest of the Great Lakes. Rover explorations have also found evidence of the former abundance of water based on analysis of surface rocks.
“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.”
Adcock and Tschauner are pursuing another round of studies using infrared light at the ALS to study actual Martian meteorite samples, and are also planning X-ray studies of these actual samples this year.
Many Martian meteorites found on Earth seem to come from a period of about 150 million to 586 million years ago, and most are likely from the same region of Mars. These meteorites are essentially excavated from a depth of about a kilometer below the surface by the initial impact that sent them out into space, so they aren’t representative of the more recent geology at the surface of Mars, Tschauner explained.
“Most of them are very similar in the rock composition as well as the minerals that are occurring, and have a similar impact age,” he said. Mars is likely to have formed about 4.6 billion years ago, about the same time as Earth and the rest of our solar system.
Even with more detailed studies of Martian meteorites coupled with thermal imaging of Mars taken from orbiters, and rock samples analyzed by rovers traversing the planet’s surface, the best evidence of Mars’ water history would be an actual Martian rock taken from the planet and transported back to Earth, intact, for detailed studies, researchers noted.[xyz-ihs snippet=”Adsense-responsive”]“It’s really important to get a rock that hasn’t been ‘kicked’” like the Martian meteorites have, said Kunz, in order to learn more about the planet’s water history.
The Advanced Light Source and Advanced Photon Source are DOE Office of Science User Facilities.
Researchers from the University of Chicago and the Carnegie Institution of Washington also participated in this study. The work was supported the DOE National Nuclear Security Administration; NASA; and the National Science Foundation.
Source: Berkeley Lab — Lawrence Berkeley National Laboratory
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