The surprising discovery of a mineral volcanic mineral on Mars forces scientists to rethink the volcanic history of the Red Planet, researchers from NASA’s Johnson Space Center and their colleagues report in a new study.
Writing in the latest edition of the journal Proceedings of the National Academy of Sciences, a group of astronomers led by Richard Morris, a planetary scientist at the Astromaterials Research and Exploration Science (ARES) division of the US space agency, said that they discovered the mineral tridymite in a rock sample collected by the Curiosity Rover at Gale Crater.
That sample, which was collected in July 2015 from a location called “Buckskin,” came as a shock to the scientists, as tridymite is generally linked to silicic volcanism, a type of activity known about on Earth but not believed to have been important or even present on the Red Planet.
By finding it, the NASA-led group (which also included scientists from the Planetary Science Institute in Arizona, the Jet Propulsion Laboratory (JPL) in California and elsewhere) has evidence suggesting Mars could have been home to explosive volcanoes capable of leaving behind the silica mineral.
Credit: NASA
Searching for alternative explanations for tridymite’s presence
“On Earth, tridymite is formed at high temperatures in an explosive process called silicic volcanism,” Morris said in a statement, adding that Mount St. Helens in Washington and the Satsuma-Iwojima volcano in Japan are two such volcanoes. “The combination of high silica content and extremely high temperatures in the volcanoes creates tridymite.”
On Mars, however, the tridymite “was incorporated into ‘Lake Gale’ mudstone at Buckskin as sediment from erosion of silicic volcanic rocks,” he added. “Significant amounts” of the mineral was detected in a sample collected by Curiosity on Sol 1060 (1,060 Martian days since the rover initially landed) by its X-ray diffraction instrument, the US space agency noted.
According to the authors, tridymite tends to crystallize at low pressures and high temperatures, and while it most likely formed as a result of silicic volcanism, there is at least one potential but less likely alternative: a series of processes including the high-temperature alteration of silica-rich residues of acid sulfate leaching could have resulted in tridymite formation.
The researchers examined Earth-based evidence to see whether or not the mineral could actually form at lower temperatures from geologically reasonable processes other than silicic volcanism, but found that this was unlikely. Nonetheless, they said that they are planning to continue to look for alternative methods to explain how tridymite could have formed without extreme heat.
“I always tell fellow planetary scientists to expect the unexpected on Mars,” said Doug Ming, ARES chief scientist at Johnson and co-author of the new study. “The discovery of tridymite was completely unexpected. This discovery now begs the question of whether Mars experienced a much more violent and explosive volcanic history during the early evolution of the planet than previously thought.”
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Image credit: NASA/JPL-Caltech/MSSS
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