Planetary scientists from Rice University, NASA’s Johnson Space Center and the California Institute of Technology have an answer to a mystery that has puzzled the Mars research community since NASA’s Curiosity rover discovered a mineral called tridymite in Gale Crater in 2016.
Tridymite is a high-temperature, low-pressure form of quartz that is extremely rare on Earth, and it was not immediately clear how a concentrated piece ended up in the crater. GaleCrater was chosen as Curiosity’s landing site because of the likelihood that it once had liquid water, and Curiosity found evidence confirming that Gale Crater was a lake as recently as 1 billion years ago.
“The discovery of tridymite in a mudstone in Gale Crater is one of the most surprising observations made by the Curiosity rover in 10 years of exploring Mars,” said Kirsten Siebach of Rice, co-author of a published study online at Earth and Planetary Science. letters “Tridymite is usually associated with evolutionary, explosive, and 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.”
Siebach, an assistant professor in Rice’s Department of Earth, Environmental and Planetary Sciences, is a mission specialist on NASA’s Curiosity team. To find out the answer to the mystery, he teamed up with two postdoctoral researchers in his Rice research group, Valerie Payré and Michael Thorpe, NASA’s Elizabeth Rampe, and Caltech’s Paula Antoshechkina. Payré, the study’s lead author, is now at Northern Arizona University and preparing to join the faculty at the University of Iowa in the fall.
Siebach and his colleagues began by reevaluating the data from each tridymite find on Earth. They also reviewed volcanic materials from models of Martian volcanism and reexamined sedimentary evidence from Gale Crater Lake. They then came up with a new scenario that matched all the evidence: Martian magma sat longer than usual in a chamber beneath a volcano, undergoing a partial cooling process called fractional crystallization that concentrated silicon. In a massive eruption, the volcano spewed ash containing the extra silicon in the form of tridymite into Gale Crater Lake and surrounding rivers. Water helped break down the ash through natural processes of chemical weathering, and water also helped sort the minerals produced by weathering.
The scenario would have concentrated tridymite, producing minerals consistent with the 2016 find. It would also explain other geochemical evidence Curiosity found in the sample, including opaline silicates and reduced concentrations of aluminum oxide.
“It’s actually a simple evolution of other volcanic rocks we’ve found in the crater,” Siebach said. “We argue that because we only saw this mineral once, and it was very concentrated in a single layer, the volcano probably erupted at the same time the lake was there. Although the specific sample we analyzed was not exclusively volcanic ash, it was ash. that had been weathered and graded by water.”
If a volcanic eruption like the one in the scenario occurred when Gale Crater contained a lake, it would mean that explosive volcanism occurred more than 3 billion years ago, while Mars was transitioning from a wetter world and perhaps warmer on the dry and barren planet it is. it’s today
“There is a lot of evidence for basaltic volcanic eruptions on Mars, but this is a more evolved chemistry,” he said. “This work suggests that Mars may have a more complex and intriguing volcanic history than we would have imagined before Curiosity.”
The Curiosity rover is still active, and NASA is preparing to celebrate the 10th anniversary of its landing next month.
The research was funded by NASA (15-MSLPSP15_2-0051, 15-MSLPSP15_0015, 80NSSC22K0732), the National Science Foundation (1947616), and Rice’s Department of Earth, Environmental, and Planetary Sciences.
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Materials provided by Rice University. Originally written by Jade Boyd. Note: Content can be edited for style and length.