The changing habitability of Mars recorded by ancient dune fields in Gale Crater

Understanding whether Mars was once capable of supporting life has been a major driving force for Mars research over the past 50 years. To decipher the ancient climate and habitability of the planet, researchers look to the rock archive – a physical record of ancient surface processes that reflect the environment and climate at the time the rocks were deposited.

In a new article published in JGR: planets, researchers from the NASA-JPL Mars Science Laboratory mission used the Curiosity rover to add another piece to the puzzle of Mars’ ancient past by investigating a unit of rocks in Gale Crater.

They found evidence of an ancient dune field preserved as a rock layer in Gale Crater, which overlies layers of rock deposited in a large lake. The rocky remains of the dune field are known today as the Stimson Formation.

The findings help scientists understand surface and atmospheric processes – such as the direction in which the wind blew across the sand to form dunes – and potentially how Mars’ climate evolved from an environment that potentially harbored life. microbial to an uninhabitable environment.

By examining the rock layers preserved through images collected by the Curiosity rover, the researchers reconstructed the shape, direction of migration and size of the large dunes, also known as draas, that occupied this part of the crater.

Models of ancient dunes, created by Imperial researchers, show the dunes nestled next to the central peak of Gale Crater – known as Mount Sharp – on a surface eroded by the wind at a five-degree angle. The research also revealed that the dunes were compound dunes – large dunes that housed their own set of smaller dunes that traveled in different directions to the main dune.

Lead author Dr Steven Banham of Imperial’s Department of Earth Sciences and Engineering said: “When the wind blows it carries grains of sand of a certain size and organizes them. in piles of sand that we recognize as sand dunes. sandy deserts, such as the Sahara, the Namibian dune field, and the Arabian deserts The force of the wind and the uniformity of its direction control the shape and size of the dune, and evidence of this can be preserved in the rock archives.

“If there is an excess of sediment transported to an area, dunes can climb as they migrate and partially bury adjacent dunes. These buried layers contain an element called “cross litter”, which can give an indication of the size of the dunes, and the direction in which they were migrating. By investigating these cross beds, we were able to determine that these strata were deposited by dunes. specific forms that form when competing winds carry sediment in two different directions.

“It is amazing that looking at the Martian rocks we can determine that two competing winds drove these great dunes across the plains of Gale Crater three and a half billion years ago. This is one of the first. evidence that we have varying wind directions – whether they are seasonal or not. “

The lower portion of Mount Sharp is made up of ancient sediments from the lake bed. These sediments accumulated on the bottom of the lake during the flooding of the crater, shortly after its formation 3.8 billion years ago. Curiosity has spent much of the past nine years studying these rocks for signs of habitability.

Dr Banham added: “Over 3.5 billion years ago, this lake dried up and sediment from the bottom of the lake was dug up and eroded to form the mountain in the center of the crater – the present day. Mount Sharp. The mountainsides are where we found evidence that an ancient dune field formed after the lake, indicating an extremely arid climate. “

However, the new findings suggest that the ancient dune field may have nurtured less life than previously thought. Dr Banham said: “The vast expanse of the dune field would not have been a particularly hospitable place for germs, and the records left behind would seldom retain evidence of life, if there was any.

“This desert sand represents a snapshot of time in Gale Crater, and we know the dune field was preceded by lakes – but we don’t know what covers the desert sandstones higher on Mount Sharp. There could be more layers deposited in arid areas. conditions, or it could be deposits associated with wetter climates. We will have to wait and see. “

Mars rovers allow researchers to explore the planet in detail like never before. Dr Banham added: “Although geologists have been reading rocks on Earth for 200 years, it is only in the last decade that we have been able to read Martian rocks in the same level of detail as we do. on earth.”

Researchers continue to examine rocks found by Curiosity and are now focusing on the wind patterns recorded by the dunes higher on Mount Sharp. Dr Banham said: “We are interested in seeing how the dunes reflect the wider climate of Mars, its changing seasons and longer term changes in wind direction. rose on Mars. “

The research was funded by the UK Space Agency and is part of the preparation for the upcoming ESA ExoMars mission to explore Mars for signs of ancient life.

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