The researchers studied the RSL on the walls of craters within the Valles Marineris canyon on Mars. They looked at several years' worth of surface-temperature measurements by THEMIS, to figure out the water concentration in the soil.
RELATED: So Liquid Water Flows on Mars -- Now What?
The researchers found that the upper limit of the water content was about 3 percent by weight - about the same concentration of water as in the surface material of the Atacama Desert in Chile and the Antarctic Dry Valleys, which are two of the driest places in the world.
The findings presented in 2015 showed evidence of "hydrated salts" (or brines) at the surface where the dark streaks are located.
"Our findings are consistent with the presence of hydrated salts, because you can have hydrated salt without having enough for the water to start filling pore spaces between particles," said Christopher Edwards, a faculty member in the Department of Physics and Astronomy at Northern Arizona University and one of the study's authors. "Salts can become hydrated by pulling water vapor from the atmosphere, with no need for an underground source of the water."
RELATED: Gullies on Mars Probably Not Carved by Water
The dark streaks have been identified at dozens of sites on the Martian surface. The dark regions typically appear in the Martian spring and summer, and fade away in the fall and winter.
"Some type of water-related activity at the uphill end still might be a factor in triggering RSL, but the darkness of the ground is not associated with large amounts of water, either liquid or frozen," Edwards said. "Totally dry mechanisms for explaining RSL should not be ruled out."
The findings appear online in the journal Geophysical Research Letters.
More From SPACE.com:
Original story on Space.com. Copyright 2016 SPACE.com, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.