The discovery began when scientists noticed dark streaks that appeared and then mysteriously disappeared on mountainsides and slopes in different areas of the planet. The streaks seemed to show up in warm seasons -- when temperatures are above minus-10 degrees Fahrenheit -- and fade as the seasons cooled.
Researchers then began using the imaging spectrometer on the Mars Reconnaissance Orbiter to study the area and detected hydrated salts on the slopes where the streaks had been.
Scientists say it's likely a shallow subsurface flow, with enough water seeping to the surface to explain the dark streaks. Now scientists will explore further to find out if there is a substantial amount of water in aquifers close to the surface.
Alfred McEwen, a principle investigator with the Mars Reconnaissance Orbiter, said he's not only looking forward to finding out more about the amount and location of the water on Mars, he's also expecting to find evidence of present-day life there.
"I think the possibility of life in the interior of Mars is rather high," he said. "It's very likely, I think, that there is life in the crust of Mars – microbes. Maybe there's something we can find close to the surface."
NASA has sent robotic rovers, including Curiosity and its predecessor Opportunity, to study Mars. Next year, NASA is scheduled to launch a mission that will probe the interior of Mars. Scientists hoep to learn whether the planet's core is solid or liquid, and why its crust is not divided into tectonic plates like the Earth's surface.
In 2020, NASA plans to launch its next super rover, that is designed to search for minerals, make oxygen on the Martian surface and continue NASA's search for signs of life.
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