The mysterious discovery of a concentrated piece of rare mineral quartz near the Gale crater on Mars by the Curiosity rover in 2016 has finally been explained.
A team of planetary scientists from Rice University, NASA’s Johnson Space Center and the California Institute of Technology (CalTech) believe that a concentrated piece of tridymite was ejected into Gale Crater by a volcano when it was still filled with water until 1 billion years ago.
The new scenario suggests that the Red Planet has a more interesting and complex volcanic history than previously thought.
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Tridymite, extremely rare on Earth, is a type of quartz – a form of silica – formed at extreme temperatures and low pressure, and how it got to the bottom of an ancient lake has baffled researchers for years.
“The discovery of tridymite in mudstone in Gale Crater is one of the most amazing observations made by the Curiosity rover in 10 years of Mars exploration,” said Rice University professor and team member Kirsten Siebach. (will open in a new tab). “Tridymite is usually associated with quartz-forming, explosive, evolved volcanic systems on Earth, but we found it at the bottom of an ancient lake on Mars, where most of the volcanoes are very primitive.”
To unravel this mystery, Siebach and her colleagues studied data on the formation of tridymite on Earth. They also looked at patterns of volcanism on the Red Planet, its volcanic materials, as well as sedimentary materials collected in Gale Crater, where the Curiosity rover landed in August 2012.
This allowed them to justify a new scenario, suggesting that the Martian magma was longer than usual in a chamber under the volcano. This allowed it to at least partially cool down, a process called fractional crystallization. (will open in a new tab) — and increased the concentration of silicon in the magma.
A massive eruption then threw ash containing this extra silicon in the form of tridymite into the lake that eventually became Gale Crater, as well as into the rivers surrounding it. This volcanic ash was then dissolved into the water of the ancient lake, which also helped to sort out the minerals contained in the ash.
(Image credit: NASA/JPL-Caltech/ASU/UA)
This would allow for the concentration of tridymite production in line with Curiosity’s 2016 discovery. The scenario proposed by the researchers would also help explain other aspects of the sample, such as its opal silicates and reduced alumina concentration.
“This is actually a direct evolution of other volcanic rocks that we found in the crater,” Zibach said. “We argue that since we only saw this mineral once and it was highly concentrated in one layer, the volcano probably erupted at the same time that the lake was there. Although the particular sample we analyzed was not exclusively volcanic ash, it was ash that had been weathered and sorted by water.”
The findings also have broader implications for the geological history of Mars. This means that the Red Planet must have experienced extreme and explosive volcanism over 3 billion years ago. This must have happened at a time when Mars was transforming from the wet and warm world into the dry and barren planet we are familiar with today.
“There is ample evidence of basaltic volcanic eruptions on Mars, but this is more advanced chemistry,” Siebach concluded. “This work suggests that Mars may have a more complex and intriguing volcanic history than we could have imagined before Curiosity.”
The team’s findings were published in the journal Earth and Planetary Science Letters. (will open in a new tab)