New study answers mystery of unexpected mineral on Mars

In 2016, NASA scientists discovered an unexpected mineral called tridymite in a rock sample at Gale Crater on Mars. The discovery was a surprise to the Mars research community because tridymite is generally associated with silicic volcanism, which is known on Earth but was not thought to be present on the Red Planet.

A new study explains the 2016 discovery of the rare mineral by NASA’s Curiosity rover. Planetary scientists from Rice University, NASA’s Johnson Space Center and the California Institute of Technology collaborated to suss out the answer to the mystery.

“The discovery of tridymite in a mudstone in Gale Crater is one of the most surprising observations that the Curiosity rover has made in 10 years of exploring Mars,” said Kirsten Siebach, an assistant professor in Rice’s Department of Earth, Environmental and Planetary Sciences, and the co-author of a study published online in Earth and Planetary Science Letters. Siebach is a mission specialist on NASA’s Curiosity team.

Siebach and colleagues reevaluated data from every reported find of tridymite on Earth. They also reviewed volcanic materials from models of Mars volcanism and reexamined sedimentary evidence from the Gale Crater, a large impact basin with a massive, layered mountain in the middle.

The researchers then came up with a new scenario that matched all the evidence – Martian magma sat for longer than usual in a chamber below a volcano, undergoing a process of partial cooling called fractional crystallization until extra silicon was available. In a massive eruption, the volcano spewed ash containing the extra silicon in the form of tridymite into the Gale Crater lake and surrounding rivers.

According to the researchers, 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 discovery by a NASA mission.

“There’s ample evidence of basaltic volcanic eruptions on Mars, but this is a more evolved chemistry. This work suggests that Mars may have a more complex and intriguing volcanic history than we would have imagined before Curiosity,” Siebach said in a statement.