Rocks show Mars once looked like Iceland

Once upon a time, the seasons of Gale Crater probably resembled those of Iceland. But no one was there to regroup over 3 billion years ago.

The former Martian crater is the subject of a study by scientists at Rice University comparing data from the Curiosity rover to places on Earth where similar geological formations have been weathered in different climates.

Iceland’s basaltic terrain and cool weather, with temperatures typically below 38 degrees Fahrenheit, have been shown to be the closest analogue to ancient Mars. The study determined that temperature had the greatest impact on how the rocks formed from sediment deposited by ancient Martian streams were weathered.

The study by former postdoctoral fellow Michael Thorpe and Martian geologist Kirsten Siebach de Rice and geoscientist Joel Hurowitz of State University of New York at Stony Brook attempted to answer questions about the forces that affected sands and mud in the old lake bed.

Data collected by Curiosity on its travels since landing on Mars in 2012 provides details on the chemical and physical states of mudstones formed in an ancient lake, but the chemistry does not directly reveal the climatic conditions when the sediments eroded in upstream. For this, the researchers had to search for similar rocks and soils on Earth to find a correlation between the planets.

The study published in JGR planets takes data from well-known and varied conditions in Iceland, Idaho and around the world to see which one best matches what the rover sees and feels in the crater that encompasses Mount Sharp.

The crater once contained a lake, but the climate that allowed water to fill it is the subject of long debate. Some argue that the start of March was hot and humid, and rivers and lakes were commonly present. Others believe it was cold and dry, and glaciers and snow were more common.

Rather, the sedimentary rocks in Gale Crater detail a climate that probably falls between these two scenarios, said Thorpe, now a Mars Sample Return Scientist to NASA’s Johnson Space Center contractor Jacobs Space Exploration. Group. “The old climate was probably freezing, but also seems to have supported the liquid water in the lakes for long periods of time.”

Researchers were surprised that there was so little weathering of rocks on Mars after more than 3 billion years, so that ancient rocks from Mars were comparable to Icelandic sediments in a river and lake today. hui.

“On Earth, the sedimentary rock disc does a fantastic job of maturing over time using chemical weathering,” Thorpe noted. “However, on Mars we see very young minerals in the mudstones which are older than any sedimentary rocks on Earth, suggesting that the weathering was limited.”

Researchers studied sediments from Idaho and Iceland directly and compiled studies of similar basaltic sediments from a range of climates across the world, from Antarctica to Hawaii, to frame the climatic conditions. they thought was possible on Mars when water was flowing into Gale Crater.

“Earth provided an excellent laboratory for us in this study, where we were able to use a range of locations to see the effects of different climatic variables on inclement weather, and the mean annual temperature had the strongest effect for the types of rocks in Gale Crater, ”said Siebach, a member of the Curiosity team who will be a Perseverance operator after the new lander lands in February. “The range of climates on Earth allowed us to calibrate our thermometer to measure the temperature on ancient Mars.

The composition of sand and mud in Iceland most closely matched Mars based on analysis via the Standard Chemical Weathering Index (CIA), a basic geological tool used to infer weathering past climate chemical and physical of a sample.

“When water flows through rocks to erode and weather them, it dissolves the more soluble chemical components of the minerals that form rocks,” Siebach said. “On Mars, we saw that only a small fraction of the fastest-dissolving elements were lost in mud compared to volcanic rocks, even though the mud has the smallest particle size and is usually the most weathered.

“It really limits the average annual temperature on Mars when the lake was present, because if it was warmer then more of that would have been flushed out,” she said.

The results also indicated that the climate changed over time from Antarctic-like conditions to become more Icelandic as fluvial processes continued to deposit sediment in the crater. This change shows that the technique can be used to track climate change on ancient Mars.

While the study focused on the lower and oldest part of the lake sediments that Curiosity explored, other studies also indicated that the Martian climate likely fluctuated and became drier over time. “This study establishes a way to interpret this trend more quantitatively, compared to the climates and environments we are familiar with on Earth today,” Siebach said. “Similar techniques could be used by Perseverance to understand the ancient climate around its landing site at Jezero Crater.”

At the same time, climate change, especially in Iceland, could shift the places on Earth best suited to understanding the past on both planets, she said.

Siebach is Assistant Professor of Earth, Environmental and Planetary Sciences at Rice. Hurowitz is an associate professor of geosciences at Stony Brook.