Boiling water forms these dark streaks on Mars, study finds
Boiling water may have carved the dark streaks on Martian slopes, a new study has found.
Previous theories posited that the streaks, known as recurring slope lineae or RSL, might have been created by dust avalanches or venting of carbon dioxide gas rather than water. However, Space.com reports, new experiments replicated conditions on Mars and point to boiling water being the cause.
The discovery may be seen as good news or bad news. While it means that Mars might still have liquid water, there could also be less of it than previously though.
Although Mars is now cold and dry, several studies suggest that liquid water once ran on the planet’s surface. However, this could still be the case, as these lines suggest that water could run down these formations every spring.
Because atmospheric pressure on the planet is very low, at about 1/100th of Earth’s, water boils easily in the thin air.
“A good example is that of Mount Everest — the atmospheric pressure at the top of Everest is 400 millibars, as opposed to around 1,000 millibars at sea level, and therefore water boils at 72 degrees Celsius [161 degrees Fahrenheit] rather than 100 degrees C [212 degrees F], meaning mountaineers cannot make a decent cup of tea,” study co-author Susan Conway, a planetary geomorphologist at the University of Nantes in France and France’s National Center for Scientific Research, said in an email. “On the Martian surface, the pressure is 5 to 10 millibars, meaning that liquid water boils no matter what the temperature is.”
Creating a mini Mars on Earth
Placing a block of ice on top of a slope made of loose, fine-grained sand, the researchers observed how the meltwater percolated through the sand. On Mars, liquid water could be produced when ground ice or seasonal frost melts. “No one had performed such experiments before, so it was both exciting and intimidating to be able to break new ground,” Conway said. This followed a month of failed experiments before the team hit upon the right formula.
“It takes a lot of testing to find a setup which adequately reproduces Martian conditions, yet can be observed and measured easily,” Conway said. “For example, we had the problem where the ice block we used for our source of water kept falling down the slope as it melted, destroying the features created by the seeping water. So we had to design an ice-cube safety belt to stop the tumbling.”
Under Earth-like conditions, the flowing water had little effect on the slope. But with the lower pressure similar to that on Mars, the water boiled vigorously, launching the sand grains into the air until their heaps collapsed, triggering avalanches.
“We already knew that water should boil under Martian conditions, but what we did not predict was that the boiling would be so intense where the water encountered the dry sediment,” Conway explained. “Our results show that a very small amount of water can actually move a disproportionately large amount of sediment, more than is possible under terrestrial conditions for the same amount of water.”
Small channels very similar to those seen on Mars could be observed in the lab set up. The experts now believe that less water is needed to create the features than was previously assumed.
“On one side of the argument, [it’s] good news, because our results show that water is still a viable candidate for forming RSL and therefore leaves the door open for the presence of liquid water at the present day,” said Conway. “On the flip side, [it’s] bad news, because they also show much less water is needed and that the water that is produced is very short-lived, therefore not a fabulous environment for microorganisms.”
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Image credit: NASA
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