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The mystery of the Martian glaciers is revealed

January 19, 2021

(Nanowerk News) In a new article published in Proceedings of the National Academies of Sciences (“Surface pebble bands indicate glaciers covered with Martian debris formed over multiple glaciations”), planetary geologist Joe Levy, assistant professor of geology at Colgate University, reveals an innovative analysis of the mysterious Mars glaciers.

On Earth, glaciers covered wide bands of the planet during the last ice age, which peaked about 20,000 years ago, before receding to the poles and leaving behind the rocks they pushed. On Mars, however, glaciers never left, remaining frozen on the cold surface of the red planet for more than 300 million years, covered in rubble. “All the rocks and sand carried on this ice have been left on the surface,” Levy says. “It’s like putting ice in a refrigerator under all that sediment.”

However, geologists have not been able to know whether all of these glaciers formed during a huge Martian ice age or in multiple separate events over millions of years. Since ice ages result from a change in the tilt of a planet’s axis (known as obliquity), answering this question could tell scientists how Mars’ orbit and climate have changed over time. of time, as well as what kind of rocks, gases, or even microbes can get trapped inside the ice. Image of the Mars Glacier This image of a glacier on Mars shows the abundance of pebbles inside the ice. High-resolution images of the surface of Mars suggest that glacial deposits covered with debris formed during multiple one-time episodes of long-term ice accumulation. Debris-covered glacial relief forms called lobate remnant (LDA) aprons are widespread on Mars. It has not been clear whether these LDAs formed during the last 300–800 million years during a single long deposition period or during multiple short-lived episodes of ice accumulation. To address this issue, Joseph Levy and colleagues used high-resolution images to map pebbles along 45 LDA on the surface of Mars. Pebbles are commonly grouped into bands of all LDAs, similar to the pebbles of ancient glaciers covered with land debris. The findings point to multiple cycles of ice accumulation and advance over the past 300-800 million years, expanding evidence of climate change on Mars beyond the 20 million-year window provided by numerical modeling. (Image: Joe Levy / Colgate University) (click image to zoom)

“There are really good models for the orbital parameters of Mars in the last 20 million years,” Levy says. “After that, the patterns tend to be chaotic.”

Levy invented a plan to examine the rocks on the surface of glaciers as a natural experiment. Since they presumably erode over time, a steady progression of larger to smaller rocks that would advance downward would point to a single, long event of the ice age.

Choosing 45 glaciers to examine, Levy acquired high-resolution images collected by the Mars Reconnaissance Orbiter satellite and set out to count the size and number of rocks. With a resolution of 25 inches per pixel, “you can see things the size of a dinner table,” Levy says.

However, even at this increase, artificial intelligence cannot determine exactly what or not a rock is on rough surfaces of glaciers; so Levy enlisted the help of ten Colgate students over two summers to count and measure some 60,000 large rocks. “We did a kind of virtual field work, walking up and down these glaciers and mapping the rocks,” Levy says.

Levy initially panicked when, far from an orderly progression of pebbles by size, the sizes of the rocks seemed to be randomly distributed. “In fact, the blogs told us a different story,” Levy says. “It didn’t matter their size; it was the way they were grouped or grouped.”

As the rocks traveled through the glaciers, they did not erode, he noticed. At the same time, they were distributed in clear bands of debris across the surfaces of glaciers, marking the boundary of separate and distinct ice flows, formed as Mars oscillated on its axis.

Based on these data, Levy has concluded that Mars has experienced between six and 20 separate ice ages over the past 300-800 million years. These findings appear in PNAS, written along with six current or former Colgate students; Colgate math teacher Will Cipolli; and colleagues from NASA, the University of Arizona, Fitchburg State University, and the University of Texas-Austin.

“This article is the first geological evidence of what the Martian orbit and obligation could have been doing for hundreds of millions of years,” Levy says. The discovery that glaciers formed over time has implications for planetary geology and even for space exploration, he explains. “These glaciers are small time capsules, capturing snapshots of what was blowing into the Martian atmosphere,” he says. “We now know we have access to hundreds of millions of years of Martian history without having to dig deep through the crust; we can only take a walk on the surface.”

This story includes any signs of life potentially present from Mars ’distant past. “If there’s any biomarker blowing, they’ll also get trapped in the ice.” At the same time, potential explorers on Mars who may need to depend on freshwater extraction from glaciers to survive will need to know that there may be bands of rocks that will make drilling dangerous. Levy and his colleagues are now in the process of mapping the rest of the glaciers on the surface of Mars, hoping that with the data they have, artificial intelligence can now train us to take on the hard work. of identification and counting of stones.

This will bring us one step closer to a complete planetary history of the red planet, including the millennial question of whether Mars could have endured life.

“There’s a lot of work to be done to find out the details of Martian climate history,” says Levy, “including when and where it was hot and humid enough for there to be brine and liquid water.”

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