Unusual, winding ravines carved into Mars's dunes are at last revealing their mysteries.
According to recent tests, these gouges are formed by the explosive sublimation of dry ice, which burrows like a mole down the slopes while blasting away sand in the process. The new findings finally explain all the oddities of the enigmatic squiggles on Mars.
According to Earth scientist Lonneke Roelofs of Utrecht University in the Netherlands, "It was like watching the sandworms in the movie Dune."
Since their initial observation in 1999, the gullies that cascade down the sand dunes of Mars have baffled astronomers. At first, experts thought that seasonal water flows were responsible for their development. But as of right now, there is no proof that liquid water flows across Mars' surface, and we are unlikely to find any in the near future.
In 2013, however, researchers presented a different theory: carbon dioxide ice, or dry ice, may have cut the runnels by sublimating as it slid down the dunes.
Although first experiments demonstrated the plausibility of this mechanism, they were unable to replicate all of the characteristics found in Martian gullies, particularly the snake-like sinuosity.
That gap did not satisfy Roelofs and her colleagues. In earlier research, they demonstrated how CO2 may propel mass outflows from steep crater walls using the Open University's Mars chamber, a confined environment that mimics Martian conditions.
The researchers once more looked to the Mars chamber to solve the gullies' issue.
The scientists used high-speed cameras to capture the outcomes of dropping chunks of dry ice onto sand slopes with varying inclinations and sand grain sizes while modifying the apparatus to replicate the thin, frigid air of Mars.
The findings demonstrated that, as observed in earlier tests, the ice glides down on a cushion of gas on slopes steeper than 25 degrees, leaving an ambiguous trail. On the other hand, the ice partially buried itself in the sand when the slope angle was less steep, below 22.5 degrees.
The sublimation process ballistically expelled the sand when the dry ice was thus buried, creating the precise features seen in the gullies on Mars.
These characteristics included a small pocket at the trail's terminus, high, pronounced levees, and the sinuous tracks, all of which had never been duplicated on Earth before.
"We experimented with several scenarios by modeling a dune slope at varying steepness angles. "We watched what happened after letting a block of CO2 ice fall from the top of the slope," says Roelofs.
"We eventually noticed results after determining the proper slope. Similar to Dune's sandworms or a burrowing mole, the CO2 ice block started to delve into the slope and descend. It appeared really odd.
Because dry ice is translucent, infrared and optical light can pass through it instead of just reflecting off its surface. But because the rock or sand beneath the ice is darker, more of the energy that reaches it is absorbed by it and reemitted as thermal (infrared) radiation.
The block of ice on top of it keeps this heat energy from escaping. Sublimation is the process by which the ice turns straight into a gas when its underside heats. With nothing else to go, this gas builds up until it explodes outward, throwing the nearby sand far away.
The researchers ran simulations to take into consideration larger blocks of ice and the gravity of Mars in order to see if their experimental observations might be scaled up to replicate the reported gullies on the planet.
According to their findings, the observed gullies could be readily replicated on the red planet by sublimating rocks up to a meter (3.3 feet) thick, which would fling sand up to 13 meters. The findings even clarify why the mechanism only functions on fine-grained slopes, which is why these gullies are only found there.
Mars has a rich CO2 atmosphere, which can coat mid-latitude dune areas with ice up to 70 cm thick during the winter.
This ice starts to warm up and sublimate in the spring. When the temperature is high enough, the blocks break off from the last of this ice, which is found on the shaded side of the dune tops, according to Roelofs.
"The ice keeps sublimating until all of the CO2 has evaporated when the blocks stop moving and reach the bottom of the slope. All that's left is a sand hollow at the dune's base.
To find out what happens when they change the conditions, the researchers now plan to conduct tests with bigger slabs of ice and various kinds of sand.
"Our closest neighbor is Mars. Near the 'green zone' of our Solar System, it is the only rocky planet. This region is precisely distant enough from the Sun to allow liquid water to exist, which is necessary for life. Thus, Roelofs believes, "questions concerning the origin of life and potential extraterrestrial life could be resolved here."
Additionally, studying how the landscape architecture of other planets were formed allows one to think beyond the conventional paradigms of Earth. This enables you to ask somewhat different questions, which can lead to fresh perspectives on processes on our planet.
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