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 Gale Crater on Mars.
Tridymite is a form of high-temperature, low-pressure quartz that is extremely rare on Earth, and it is unclear how a concentrated portion of it ended up in the Martian crater.
Scientists chose Gale Crater as a landing site for NASA’s Curiosity, due to the possibility that it contained ancient liquid water. The craft recently found evidence that Gale Crater was a lake a billion years ago.
“The discovery of tridymite in stone, Kristin Seebach, assistant professor in the Department of Earth, Environmental and Planetary Sciences at Rice University, co-author of the study published online in the journal Earth and Planetary Science Letters and a mission specialist on NASA’s Curiosity team, said. Mud in Gale Crater is one of the most surprising observations Curiosity has made in its 10 years of Mars exploration. Tridimite is usually associated with advanced, explosive volcanic systems composed 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 reassessing the data from every reported find of tridymite on Earth.
The team also reviewed volcanic material from Martian volcano models and re-examined sedimentary evidence from Lake Gale. And they came up with a new scenario that matches all the evidence, which is that Martian magma stayed longer than usual in a chamber beneath the volcano, undergoing a partial cooling process called microcrystallization until additional silicon is available.
In a massive eruption, the volcano spewed ash containing extra silicon onto the tridemite into Gale Crater Lake and surrounding rivers.
The water helped to break down the ash through the natural processes of chemical weathering, and the water also helped to sort out the minerals resulting from weathering.
This scenario is also explained by other geochemical evidence present in the sample, including opaline silicate 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 because we only saw this mineral once, and it was so concentrated in one layer, it is possible that the volcano erupted around the same time the lake was there. Although the specific sample that we analyzed was not exclusively volcanic ash, it was ash that was weathered and sorted by water.”
And if a volcanic eruption occurred like the one in the scenario when Gale Crater contained a lake, this means that the erupting volcanoes occurred more than 3 billion years ago, while Mars was moving from a wetter, and perhaps warmer, world to a dry planet and barren nature as it is today.
“There is plenty of evidence for basaltic eruptions on Mars, but this is a much more sophisticated chemistry,” Seebach said. This work suggests that Mars may have a much 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.
