Where does Mars’ water come from? We know about the Martian polar ice caps. But what about the dark streaks NASA found in 2015? A new study is trying to figure out where this apparent water is coming from. First, a little background.

Last September, NASA made headlines when it confirmed evidence of liquid water flowing on Mars. Scientists kept seeing mysterious dark streaks (recurring slope lineae) on the surface from images captured by the Mars Reconnaissance Orbiter.

Mars dark streaks

“We found the hydrated salts only when the seasonal features were widest, which suggests that either the dark streaks themselves or a process that forms them is the source of the hydration. In either case, the detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks,” said Lujendra Ojha of the Georgia Institute of Technology.

The hydrated salts would act just like the salts used on icy streets in the winter cause ice and snow to melt quicker. It lowers the freezing point of a liquid brine beneath the surface. And scientists say it’s likely a shallow subsurface flow is responsible for the darkened lines seen in the above image.

Alright, now let’s fast forward to today. A new study published in the Journal of Geophysical Research tried to figure out where the water from these dark streaks is coming from. They studied a region of Mars near the equator called Valles Marineris. And they found thousands of these dark streaks (the blue dots in the image below show where dark streaks were found).

Mars canyon

Some of their locations were atop canyon ridges and mountains. Which makes it hard to explain how shallow ice deposits exist in these areas given the warmer temperatures in this region.

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The first image shows dark streaks forming in a crater wall. At the time, scientists believed ice melting just below the surface was the cause. But with these streaks seen atop peaks near the equator, that explanation is looking less likely.

One potential way for these streaks to form is from salts pulling water vapor out of Mars’ atmosphere. Some of the dark streaks investigated by the team of scientists had bright streaks near them. This could be from salt left behind after the brine evaporated.

“There are problems with the mechanism of pulling water from the atmosphere, too,” said lead author Matthew Chojnacki. A JPL post goes into further detail:

If it is seeping water that darkens RSL, the amount of liquid water required each year to form the streaks in the studied portion of Valles Marineris would total about 10 to 40 Olympic-size swimming pools (about 30,000 to 100,000 cubic meters), the researchers estimate. The amount of water vapor in the atmosphere above the whole Valles Marineris region is larger than that, but researchers have not identified a process efficient enough at extracting water from the atmosphere to get that much onto the surface.

Chojnacki talked more about how interactions between the atmosphere and surface could be responsible for the high number of dark streaks in the area. “But a mechanism to make that connection is far from clear,” he said.

Scientists are still struggling to explain how these features are formed. It doesn’t appear underground water can be responsible. At least, not for the features atop canyon ridges and peaks. The team continues to study the dark streaks and are performing experiments simulating them on Earth.

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Unfortunately, we can’t just send a rover to these areas. Since liquid water is believed to be flowing in these streaks, NASA won’t risk contaminating an area like this with bacteria from Earth. No matter how well they sterilize a rover, they can’t 100% guarantee it is bacteria-free.

Until we send folks to the red planet, scientists are stuck studying them from afar.

Image credits: NASA

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