"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."
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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.