The mysterious discovery of a concentrated chunk of rare mineral quartz in the Gale Crater region of Mars by the Curiosity rover in 2016 has finally been explained by researchers.
A team of planetary scientists from Rice University, NASA’s Johnson Space Center and the California Institute of Technology (CalTech) believe the concentrated chunk of tridymite was spewed into Gale Crater by a volcano while it was still filled with water as long as 1 billion years ago.
The new scenario suggests that the Red Planet has a more interesting and complex volcanic history than previously believed.
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Tridymite, which is extremely rare on Earth, is a type of quartz – a form of silica – generated at extreme temperatures and low pressures, and how it arrived in an ancient lake bed has troubled researchers for years.
“The discovery of tridymite in a mudstone at Gale Crater is one of the most startling observations the Curiosity rover has made in 10 years of Mars exploration,” said Kirsten Siebach, a Rice University professor and member of the team. statement (opens in a new tab). “Tridymite is usually associated with evolved quartz-forming volcanic systems on Earth, but we found it at the bottom of an ancient lake on Mars, where most volcanoes are very primitive.”
To solve this mystery, Siebach and his colleagues looked at data regarding the formation of tridymite on Earth. They also examined patterns of volcanism on the Red Planet, its volcanic materials, as well as sedimentary evidence collected from Gale Crater where the Curiosity rover touched down in August 2012.
This allowed them to devise a new scenario suggesting that Martian magma had been sitting longer than usual in a chamber beneath a volcano. This allowed it to cool at least partially – a process called fractional crystallization (opens in a new tab) – and increased the silicon concentration of the magma.
A massive eruption then spewed ash containing this extra silicon in the form of tridymite into the lake that would become Gale Crater, as well as its surrounding rivers. This volcanic ash was then decomposed by the water of the old lake which also helped to sort out the minerals contained in the ash.
This would have concentrated the manufacture of tridymite in line with Curiosity’s discovery in 2016. The scenario put forward by the researchers would also help explain other aspects of the sample like its opaline silicates and reduced concentrations of aluminum oxide.
“It’s actually a direct evolution of other volcanic rocks that we found in the crater,” Siebach said. “We argue that because we only saw this mineral once and it was highly concentrated in a single layer, the volcano probably erupted at the same time the lake was there. Although the specific sample that 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 more than 3 billion years ago. This would have been during a time when Mars was changing from a humid and warm world to the dry and barren planet we know today.
“There is plenty of evidence for basalt volcanic eruptions on Mars, but it’s more advanced chemistry,” Siebach concluded. “This work suggests that Mars may have a more complex and intriguing volcanic history than we would have imagined before Curiosity.”
The team’s findings were published in the journal Letters on the sciences of the Earth and the planets. (opens in a new tab)