NASA Finds 'Definitive' Liquid Water on Mars

Dark streaks that appear and vanish seasonally are made of salty water, new observations show.

photographs by NASA, JPL Cal-tech, Univ. of Arizona

The steep slopes of Coprates Chasma on Mars are marked by dark streaks called recurring slope lineae, which scientists have discovered are produced by flowing saltwater.

Photograph by NASA, JPL Cal-tech, Univ. of Arizona

In Mars' Hale crater, 100-meter-long dark streaks (brown) are formed by flowing, liquid saltwater. They appear in warm seasons and quickly fade.

Photograph by NASA, JPL, University of Arizona

Those features could all be explained if water were seeping down Martian slopes and darkening their surface, says University of Arizona’s Alfred McEwen. There was just one problem: “We had no direct detection of water,” he says. “That was just our best guess.”

Now, the team has associated the streaks with hydrated salts in four different areas where the streaks appear. The salts are called perchlorates and have water molecules trapped in their crystal structures.

“The presence of hydrated salts in these flows means that the streaks are forming due to contemporary water,” Ojha says.

Is Mars Sweating?

A big question swirls around the origin of that water: Where is it coming from? One possibility is that the seeps are fueled by an aquifer or melting subsurface ice. These scenarios would have Mars essentially sweating, with saltwater seeping from its pores and trickling down slopes as the planet warms.

The water might also be atmospheric in origin, which is the hypothesis the team seems to favor. In this scenario, surface salts absorb water vapor in the Martian atmosphere.

“If the humidity in the Martian atmosphere gets high enough, perchlorate salts will absorb the atmospheric water until the salt dissolves forms a liquid solution,” says Mary Beth Wilhelm of NASA’s Ames Research Center.

Wherever its source, it's no surprise that there’s water on Mars. Entire Martian landscapes have been sculpted by the stuff (including an ancient mile-deep sea)—albeit billions of years ago when the planet was warmer and more watery. The fleet of spacecraft currently exploring the Martian surface continually return data suggesting that water was once common. (In 2012, Curiosity rover found direct evidence for flowing water on Mars—in the past.)

But until now, evidence has been scarce for flowing water at the surface today. What it means, in the bigger picture of planetary exploration and the search for life beyond Earth, is still a mystery.