Scientists solve the mystery of a rare mineral that NASA discovered on Mars 6 years ago
A team of planetary scientists has come up with an explanation that may solve a mystery that has baffled the scientific community since 2016, when the Curiosity rover discovered a rare mineral called tridimite in the Gale Crater on Mars.
Tridymite is a high-temperature, low-pressure form of quartz that is extremely rare on Earth, and it is not clear how a concentrated portion of it ended up in a Martian crater.
Scientists chose Gale Crater as the landing site for NASA's Curiosity, due to the possibility that it contained liquid water in the past. The rover recently found evidence that Gale Crater was a lake a billion years ago.
“The discovery of tridymite in the Earth and Planetary Science Letters journal,” said Christine Seebach, assistant professor in the Department of Earth, Environmental, and Planetary Sciences at Rice University, a co-author of the study published online in the journal Earth and Planetary Science Letters, and a mission specialist on NASA’s Curiosity team. Mud in Gale Crater is one of the most surprising observations made by the Curiosity rover in 10 years of Mars exploration.
Tridimite is commonly associated with highly developed and explosive volcanic systems made of quartz on Earth, but we found it at the bottom of an ancient lake on Mars, where most volcanoes are very primitive.
Seebach and her colleagues began by re-evaluating the data from each reported discovery of tridimite on Earth.
The team also reviewed volcanic material from models of Martian volcanoes and re-examined sedimentary evidence from Lake Gale. And they came up with a new scenario that matches all the evidence, which is that the Martian magma stayed longer than usual in a chamber at the bottom of the volcano, undergoing a partial cooling process called partial crystallization until additional silicon was available.
In a massive volcanic eruption, the volcano spewed ash containing additional silicon onto tridimite in Gale Crater Lake and surrounding rivers.
The water helped break down the ash through the natural processes of chemical weathering, and the water also helped sort out the minerals from weathering.
This scenario also explains the other geochemical evidence present in the sample, including silicate opaline and low concentrations of aluminum oxide.
"It's actually a direct evolution of other igneous rocks that we found in the crater," Seebach said. We argue that since we only saw this mineral once, and it was very concentrated in one layer, the volcano probably 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 filtered by water.”
And if a volcanic eruption occurred like the one that occurred in the scenario when the Gale crater contained a lake, this means that the explosive volcanism occurred more than 3 billion years ago, while Mars was moving from a wetter, perhaps warmer, world to a dry planet and barren nature as it is. today.
"There is a lot of evidence of basaltic volcanic eruptions on Mars, but this is a more sophisticated chemistry," Seebach said. This work indicates 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.
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