Liquid Water on Mars is Big News

By Seth Shostak, Senior Astronomer

Water on Mars?  It’s an old story from the Red Planet, and the facts is that landers have frequently found water in the form of ice just below the surface.

But NASA has just announced new results based on high-resolution imagery from NASA’s Mars Reconnaissance Orbiter satellite showing that liquid water also occasionally flows on the surface.  This conclusion is based on spectroscopic analysis of dark, seasonal streaks on the sides of craters and other features known as “recurrent slope lineae,” which look like long fingers that appear and lengthen during the martian summers.  For years, there’s been argument about what is causing the lineae: Is it really water, or could it be something else – even dry material slowly tumbling down the slopes?

The argument is apparently over.  The new results come down heavily in favor of water – highly salty, yes, but liquid water.

liquid on mars
These dark, narrow, 100-meter-long streaks called recurring slope lineae flowing downhill on Mars are inferred to have been formed by contemporary flowing water. Recently, planetary scientists detected hydrated salts on these slopes at Horowitz crater, corroborating their original hypothesis that the streaks are indeed formed by liquid water. (Photo: NASA/JPL/University of Arizona)

The source of the water is still unclear, but a favored explanation is that it’s seeping out of underground aquifers – reservoirs of water hulking in the crust of Mars.  

That has obvious, and encouraging, implications for any future efforts to send humans to the Red Planet.  A simple drilling rig might be all that’s necessary to get to supplies of precious water, not just for drinking but also for rocket fuel.

But another important consequence of this discovery is its effect on how we search for evidence of martian life.  Rather than continuing to methodically learn more about the history of the planet in the hope of knowing where to look for remnants of ancient life, this suggests that simply getting a probe to the site of the lineae might offer the chance of finding biology, not from 3 or 4 billion years ago, but still extant microbes in the hidden underground reservoirs of the Red Planet.