We May Finally Understand How a Strange, Rare Mineral on Mars Came to Exist

In 2016, the Curiosity rover came across something really peculiar in Gale Crater on Mars.

On the slope of Mount Sharp, where Curiosity labored, were large quantities of a rare mineral; rare, at least, here on Earth. Tridymite, a form of quartz, only seems to form extremely seldom, and under high temperatures, such as those you might find in magma.

Although Mars shows extensive evidence of past basaltic volcanic activity in some regions, the once putatively water-filled Gale Crater is not one of those regions, leading scientists to puzzle about how the mineral came to be there.

Now a team led by planetary scientist Valerie Payré of the University of Arizona have figured out the mystery: that tridymite could have come from a single, explosive volcanic eruption, around 3.0 to 3.7 billion years ago.

“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 Mars geologist Kirsten Siebach of Rice University.

“Tridymite is usually associated with quartz-forming, explosive, evolved volcanic systems on Earth, but we found it in the bottom of an ancient lake on Mars, where most of the volcanoes are very primitive.”

Because we can’t actually get to Mars, the scientists had two tools for figuring out the mystery: tridymite deposits found here on Earth, and the mineral samples collected from Gale Crater and Mount Sharp – the peak at the crater’s center – by Curiosity, which sends data on its finds back to Earth.

So that’s where Payré, then at Rice University, and her colleagues turned.  …