NASA has confirmed our suspicions: There's probably liquid water on Mars today. The landmark finding makes the notion of life on the Red Planet all the more plausible.
"Water is essential to life as we know it," the researchers behind a study published today in Nature Geoscience today write. "The presence of liquid water on Mars today has astrobiological, geologic and hydrologic implications and may affect future human exploration."
The study, led by geomorphologist Lujendra Ojha of Georgia Tech, utilises new data collected by the Mars Reconnaissance Orbiter to show evidence for recurrent seepage of liquid water along Martian crater walls.
Images collected by the Reconnaissance Orbiter's HiRISE camera show that "recurrent slope lineae" — dark streaks that resemble flow paths on Martian slopes — appear to be seasonal, fading when inactive and reappearing annually over multiple Martian years. These features alone hint at the presence of flowing water, but the real clincher comes in the form of spectral data, collected by the Reconnaissance Orbiter's Compact Reconnaissance Imaging Spectrometer: Hydrated perchlorate salts within the flow paths. Hydrated salts (which contain water in their molecular structure) are powerful evidence of evaporated brine, possibly from an underground reservoir.
Darkening lines (known as RSL) moving down a slope as the temperature rises, possibly representing spring and summer salt water flows on Mars, NASA/JPL
"Something is hydrating these salts, and it appears to be these streaks that come and go with the seasons," Ojha said in a statement. "This means the water on Mars is briny, rather than pure. It makes sense because salts lower the freezing point of water. Even if RSL are slightly underground, where it's even colder than the surface temperature, the salts would keep the water in a liquid form and allow it to creep down Martian slopes."
It's well-established that ancient Mars used to be a much warmer, wetter place. It might have even been covered by a global ocean. But for years, scientists have debated whether liquid water could exist on the frigid, dry Martian surface today. If liquid water were present on modern Mars, that would substantially bolster the case for microbial life.
NASA has been teasing us with this news since a press release last week said that the space agency would be announcing a 'major science finding' that solves a longstanding Martian mystery. The timing of the announcement was well calculated: With the opening of the NASA-endorsed feature film The Martian this week, NASA is doing everything in its power to drum up public excitement about a real mission to Mars in the 2030s.
And what's more exciting than the prospect of alien microbes?
[Read the full scientific paper at Nature Geoscience]
Top image: Dark, narrow, 100 meter-long streaks called flowing downhill on Mars are inferred to have been formed by contemporary flowing water, via NASA/JPL/University of Arizona