麻豆淫院

Did life really exist on Mars after all? Unfortunately, there is no conclusive evidence for this yet. Nevertheless, it would seem that some form of life was the driving force behind the mysterious Martian dune gullies. Earth scientist Dr. Lonneke Roelofs from Utrecht University has investigated how these gullies were formed. In a test setup, she observed that blocks of CO₂ ice "dug" these gullies in a unique way.

"It felt like I was watching the sandworms in the film Dune," Roelofs says. Her findings are in Geophysical Research Letters.

Other researchers had previously suspected that these blocks could play a role in the formation of the gullies. Roelofs has now proven this by having CO₂ ice blocks actually dig those gullies in an experiment鈥攁 phenomenon that we do not know here on Earth and that had never been observed by anyone before.

Sublimation

Ice forms on the dunes during the Martian winter when it is minus 120 degrees Celsius. At the end of winter, the dune slopes heat up and blocks of ice break off, some of which are up to a meter long. Due to the thin atmosphere and the large temperature difference between the warm dune sand and the ice, the bottom side of the ice immediately turns into gas, a process referred to as sublimation. As a kilo of gas requires far more space than the same weight of ice, the ice explodes, so to speak.

"In our simulation, I saw how this high gas pressure blasts away the sand around the block in all directions," says Roelofs. As a result, the block digs itself into the slope and becomes trapped in a hollow surrounded by small ridges of settled sand. "However, the sublimation process continues, and so the sand keeps on being blasted in all directions."

Due to this process, the block gradually moves downwards, leaving a long, deep gully with small sand ridges on either side behind it. This is exactly the type of gully that is also found on the Red Planet.

Lonneke Roelofs investigates the processes that form the landscape on the planet Mars. For example, last year she published her research into sublimation of CO₂ ice as a driver of Martian debris flows. These flows cut deep gullies on crater walls.

"But the gullies from this research looked different," explains Roelofs. "Therefore, a different process was behind this, but which? That is what I set out to discover."

Mars chamber

Together with master student Simone Visschers, she traveled to the English city of Milton Keynes to solve the mystery behind these unusual sand gullies. The Open University has a "Mars chamber": a facility for simulating Martian conditions.

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"We tried out various things by simulating a dune slope at different angles of steepness. We let a block of CO₂ ice fall from the top of the slope and observed what happened," states the researcher. "After finding the right slope, we finally saw results. The CO₂ ice block began to dig into the slope and move downwards just like a burrowing mole or the sandworms from Dune. It looked very strange."

But how exactly do these blocks of ice form? "The CO₂ ice blocks form on the desert dunes halfway down the southern hemisphere of Mars. During the winter, a layer of CO₂ ice forms over the entire surface of the dune field, sometimes up to a thickness of 70 cm. In spring, this ice begins to warm up and sublimate.

"The last remnants of this ice are located on the shaded side of the dune tops, and that is where the blocks break off from once the temperature is high enough. Once the blocks reach the bottom of the slope and stop moving, the ice continues to sublimate until all the CO₂ has evaporated. What remains is a hollow in the sand at the bottom of the dune," says Roelofs.

Why Mars?

Why does this planet fascinate people so much? "Mars is our nearest neighbor. It is the only rocky planet close to the 'green zone' of our solar system. This zone lies exactly far enough from the sun to make the presence of liquid water possible, which is a prerequisite for life. Questions about the origin of life, and possible extra-terrestrial life, could therefore be solved here," says Roelofs.

"Also, conducting research into the formation of landscape structures of other planets is a way of stepping outside the frameworks used to think about Earth. This allows you to pose slightly different questions, which in turn can deliver new insights for processes here on our planet."