NASA’s Curiosity rover discovered a mineral called tridymite in Gale Crater of the Red Planet in 2016, and since then, a mystery has puzzled the Mars research community. Now, planetary scientists from Rice University, NASA’s Johnson Space Center, and the California Institute of Technology have found an answer to the mystery.
Tridymite is a high-temperature, low-pressure form of quartz, and is extremely rare on Earth. Scientists were not immediately able to determine how a concentrated chunk of tridymite ended up in the Gale Crater.
NASA chose Gale Crater as Curiosity’s landing site due to the likelihood that it once held liquid water. The rover found evidence that confirmed Gale Crater was a lake as recently as one billion years ago.
A new study led by researchers at Rice University has found that tridymite was formed on Mars as a result of an explosive volcanic eruption. The study was published online in Earth and Planetary Science Letters.
Discovery Of Tridymite In Gale Crater Is One Of The Most Surprising Observations Made By Curiosity
In a statement released by Rice University, Kirsten Siebach, co-author of the study, said 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. She added that tridymite is usually associated with quartz-forming, explosive, evolved volcanic systems on Earth, but the scientists found the rare mineral in the bottom of an ancient lake on Mars, where most of the volcanoes are very primitive.
Siebach is an assistant professor in Rice University’s Department of Earth, Environmental and Planetary Sciences, and is a mission specialist on NASA’s Curiosity team. She teamed up with two postdoctoral researchers in her research group, Valerie Payre and Michael Thorpe, and also with NASA’s Elizabeth Rampe and Caltech’s Paula Antosheckina to find the answer to the mystery about how a concentrated chunk of tridymite ended up in a crater on Mars.
The team of researchers re-evaluated data from every reported find of tridymite on Earth, and reviewed volcanic materials from models of Mars volcanism. They re-examined sedimentary evidence from the Gale Crater lake.
How Was Tridymite Formed On Mars?
According to the study, the researchers came up with a new scenario that matched all the evidence. They found that Martian magma sat for longer than usual in a chamber below a volcano. The magma underwent a process of partial cooling called fractional crystallisation until extra silicon was available. Fractional crystallisation is the process of separating the components of a solution on the basis of their different solubilities, through evaporation of the solution until the least soluble component crystallises out. This process defines the structure of rocks.
A massive volcanic eruption spewed ash containing the extra silicon in the form of tridymite into the Gale Crater lake and surrounding rivers. The ash was broken down through the action of water, and natural processes of chemical weathering. Water also sorted the minerals produced by weathering.
These events would have concentrated tridymite, and produced other minerals consistent with the 2016 discovery. Opaline silicates and reduced concentrations of aluminium oxide found in the sample were also produced due to the volcanic eruption and subsequent natural processes.
Siebach said it is actually a straightforward evolution of other volcanic rocks the researchers found in the crater. She added that the team only saw this mineral once, and it was highly concentrated in a single layer.
Siebach explained that the volcano probably erupted at the same time the lake was there, and although the specific sample the team analysed was not exclusively volcanic ash, it was ash that had been weathered and sorted by water.
According to the study, if a volcanic eruption like the one explained in the study occurred when Gale Crater contained a lake, it would mean explosive volcanism occurred more than three billion years ago. This was the time when Mars was transitioning from a wetter and warmer world to the dry and barren planet it is today.
Siebach said there is ample evidence of basaltic volcanic eruptions on Mars, but this is a more evolved chemistry. She explained that the work suggests that Mars may have a more complex and intriguing volcanic history than scientists would have imagined before Curiosity.