Dark seasonal streaks on slopes near the Martian equator may be a sign of flowing salt water on Mars, liquid runoff that melts and evaporates during the planet's warmer months, scientists say.
NASA's Mars Reconnaissance Orbiter spotted the dark streaks on Mars as they formed and grew in the planet's late spring and summer seasons, when the Martian equatorial region receives the most sunlight. The streaks then faded the next season as cooler temperatures prevailed.
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These seasonally occurring flows - known as Recurring Slope Lineae - were previously seen on Martian slopes at mid-latitudes, but the MRO spacecraft has now detected them near the equator of the Red Planet. While there have been no direct detections of liquid water, the new findings hint at a surprisingly active water cycle on Mars today, said study leader Alfred McEwen, a professor of planetary geology at the University of Arizona in Tucson. [Photos: The Search for Water on Mars]
"Now we've found them in equatorial regions," McEwen told SPACE.com. "This is more surprising, given peoples' expectations that the equatorial region was completely dry. It suggests there may be much more water in the near-surface crust than we imagined before."
Flowing Water On Mars?
The dark, narrow lines were observed on long, steep slopes in Valles Marineris, an extensive series of canyons located along the equator of Mars. In some cases, the fingerlike streaks stretched nearly 3,700 feet (1,130 meters).
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The discovery is detailed in the Dec. 10 edition of the journal Nature Geoscience and will be discussed today at the annual American Geophysical Union meeting in San Francisco.
Researchers are still puzzling over the likely cause of these tantalizing streaks, but McEwen said they could be produced by the melting and subsequent evaporation of frozen salty water trapped deep in the planet's crust.
But, much is still unknown about whether the streaks are actually caused by liquid water, and if so, where the water is coming from. So far, researchers say the best explanation is that the liquid is a salty, or briny, solution. Salty water can stay liquid at colder temperatures, which means brines could conceivably flow on the frigid surface of Mars.
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"Water should be rapidly evaporating, so it's difficult to explain long flows unless it's sufficiently salty water," McEwen said.
Also, Mars has a very dry atmosphere, which makes it unlikely that freshwater flows on the surface of the planet, said Vincent Chevrier, a planetary scientist at the University of Arkansas in Fayetteville, who was not involved with the new study.
"Water has a tendency to evaporate very quickly when it's exposed at the surface," he told SPACE.com.