A team of planetary scientists has come up with an explanation that could solve a mystery that has baffled the scientific community since 2016, when the Curiosity rover discovered the rare mineral tritymite in Gale Crater on Mars.

Tridymite is a form of high-temperature, low-pressure quartz that is extremely rare on Earth, and it’s unclear how its enriched portion ended up in a Martian crater.

Scientists chose Gale Crater as the landing site for NASA’s Curiosity because it may have contained ancient liquid water. The craft recently discovered evidence that Gale Crater was a lake a billion years ago.

“The discovery of tridiimide in the rock is one of the most surprising observations Curiosity has made during its 10-year Mars mission,” said Christine Seebach, assistant professor in Rice University’s Department of Earth, Environmental and Planetary Sciences, co-author of the study published online in the journal Earth and Planetary Science Letters, and mission specialist for NASA. mud in. Tridymite is usually associated with advanced, eruptive volcanic systems composed of quartz on Earth, but we found it at the bottom of an ancient lake on Mars, where most of the volcanoes are much older.

Seebach and his colleagues began by reevaluating the data from every report of tridimite on Earth.

The team reviewed volcanic material from Martian volcano samples and re-examined sediment evidence from Gale Lake. And they came up with a new scenario that fits all the evidence, namely that Martian magma stayed in a chamber beneath the volcano longer than usual, undergoing a partial cooling process called microcrystallization until more silicon became available.

In a major eruption, the volcano spewed additional silicon-rich ash over the Tridemite into Gale Crater Lake and surrounding rivers.

The water helped break down the ash through the natural processes of chemical weathering, and it also helped sort the weathered minerals.

This scenario is also illustrated by other geochemical evidence in the sample, including low concentrations of opaline silicate and aluminum oxide.

“It’s actually a direct evolution of other igneous rocks we’ve found in the crater,” Seebach said. We only saw this mineral once, and it was so thick in one layer that we argue that the volcano probably erupted at the same time as the lake. Although the particular sample we analyzed is not volcanic ash, it is weathered and water-sorted ash.

If a volcanic eruption like the one in Gale Crater had a lake, it would mean that the volcanoes erupted 3 billion years ago when Mars was moving from a wetter and warmer world to a drier one. And barren nature it is today.

“There is a lot of evidence for basaltic eruptions on Mars, but this is very sophisticated chemistry,” Seebach said. This work suggests that Mars may have a more complex and interesting volcanic history than we imagined before Curiosity.

Curiosity is still active on the Red Planet, and NASA is preparing to celebrate the 10th anniversary of its landing next month.