As much as a fifth of Mars may have been once covered with water—and there may still be some liquid water on the planet, NASA announced today. That is good news if we humans ever hope to find life there, or to colonize the red planet.
In 2011, Lujendra Ojha at the Georgia Institute of Technology and colleagues at labs connected with NASA observed what looked like clear evidence of liquid water. It has taken them three years after observing those images to announce today, in a study published in Nature Geoscience, that they have the strongest evidence yet that there may indeed be liquid water on Mars.
What Ojha and his colleagues observed in 2011 are called recurring slope lineae (RSL), and they are found at many places along Mars’ equator. Annual seasonal changes of warming and cooling on the red planet lead to the formation of these patterns, and the presence of liquid water has been one of the strongest hypotheses put forth to explain the flow pattern.
To prove that is indeed the case, scientists would need to find liquid water. That is nearly impossible given the temperature (an average of -63°C) and low pressure (about 0.6% that of Earth) on Mars. Whatever water exists, mostly on the polar caps, seems to be in the solid form.
However, if there are enough salts present on those slopes, then water could be there in the form of brine. Salt can lower the melting point of the mixture by as much as 70°C and possibly create the flowing patterns seen. So all that would be needed to confirm this hypothesis is the presence of salts that contain water molecules.
To find them, Ojha and his colleagues used data from the instruments onboard the Mars Reconnaissance Orbiter. That was a tricky proposition: The resolution of the spectrometer is 18m per pixel, and most of the RSL are smaller in size.
But after much jiggery-pokery, Ojha and his colleagues have been able to believe that their data do indeed reveal the presence of hydrated salts (magnesium perchlorate, sodium perchlorate, and magnesium chloride) in four different locations in the equatorial region of Mars.
“This is really tantalizing,” Sanjeev Gupta of Imperial College London told Quartz. “Many have claimed the existence of water in RSL, but this is the first time that chemical evidence has been shown to exist.”
How the water needed to form brine finds its way to the RSL is not something that the researchers have been able to answer. One theory is that there may be underground aquifers. But that is unlikely given that RSL are seen on top of peaks where underground aquifers can’t exist. A more plausible theory is that salts suck the water out of the atmosphere in summer months (a process known as deliquescence).
In Atacama dessert, one of the driest places on Earth, it is through deliquescence that salts absorb water. What is particularly thrilling in relation to the Mars discovery is that even in such salty conditions, we have been able to find the existence of microbial communities. If what Ojha and his colleagues have found is indeed correct, then they also raise the possibility of finding microbial life on Mars.
The next step, Gupta said, would likely be to find ways to improve the resolution of instruments that can confirm the findings. No robotic missions are yet planned to the RSL, but perhaps space agencies should consider planning one.