Explanation to a surprising finding on Mars in 2016

Aug. 1 () –

Planetary scientists have answered a puzzling mystery on Mars since NASA’s Curiosity rover discovered a mineral called tridymite at 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 portion ended up in the crater. Gale Crater was chosen as Curiosity’s landing site because of the likelihood that it once contained liquid water, and Curiosity found evidence that confirmed Gale was a lake as recently as a billion years ago.

“The discovery of tridymite in a mudstone in Gale Crater is one of the most surprising observations the Curiosity rover has made in 10 years of exploring Mars“, said it’s a statement Kirsten Siebach of Rice, co-author of a study published online at Earth and Planetary Science Letters. “Tridymite is generally associated with evolved, explosive, and quartz-forming volcanic systems on Earth, but we found it at the bottom of an ancient lake on Marswhere most of the 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 discover the answer to the mystery, partnered with two postdoctoral fellows in his Rice research group, Valerie Payré and Michael Thorpe, Elizabeth Rampe of NASA, and Paula Antoshechkina of Caltech. Payré, the lead author of the study, is now at Northern Arizona University and is preparing to join the University of Iowa faculty in the fall.

Siebach and his colleagues began by reevaluating the data for every reported find of tridymite on Earth. They also reviewed volcanic materials from models of Mars volcanism and reexamined sedimentary evidence from Gale Crater Lake. Then they came up with a new scenario that matched all the evidence: Martian magma sat for longer than usual in a chamber under a volcano, undergoing a partial cooling process called fractional crystallization until additional silicon became available.

In a massive eruption, the volcano spewed ash containing the extra silicon in the form of tridymite into Gale Crater Lake and surrounding rivers. The water helped break down the ash through natural chemical weathering processes and 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 opal 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 likely 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 sorted by water”.

If a volcanic eruption like the one in the scenario occurred when Gale Crater contained a lake, it would mean that the explosive volcanism occurred more than 3 billion years ago, while Mars was in transition from a wetter and perhaps warmer world to the dry and arid planet that it is today.

“There is ample evidence for basaltic volcanic eruptions on Mars, but this is 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.”