Despite regularly dipping to temperatures as low as -100 degrees Celsius, Mars appears to be harbouring small amounts of liquid water, according to new evidence collected by the Curiosity rover.
While the discovery of ice on Mars back in 2002 was a major breakthrough at the time, it makes sense that if we were going to find water on the Red Planet, it was gonna be frozen solid. But how does liquid water even have the chance to form in such a frigid atmosphere?
Researchers analysing the Curiosity data, led by planetary scientist Javier Martín-Torres from the Luleå University of Technology in Sweden, suspect that salt could be at play in tiny pockets of Martian water, accumulating in such quantities that it lowers the freezing temperature of water, so things have to get a whole lot colder than they do on Earth in order for the liquid water to solidify.
Evidence of perchlorate salts - which form when a perchlorate ion made from one chlorine atom and four oxygen atoms combines with magnesium, calcium or iron - were detected on Mars back in 2008, so salt could very well be forming enough heavy crusts on the surface for this theory to work.
Publishing in the journal Nature Geoscience, the researchers describe how they think Mars's perpetual water cycle works. It starts out with water vapour in the atmosphere that gets absorbed by the large amounts of salt on the surface. At night, when the subzero temperatures set in, these salts are so saturated by water vapour, that they form "liquid brines in the uppermost 5 cm of the subsurface". These liquid pools remain until the daytime temperatures - which can go beyond 100 degrees Celsius - turning them back into vapour.
Interestingly, Martín-Torres told Victoria Turk at Motherboard that the place where they found evidence for liquid water was at the Gale crater, which is one of the hottest and driest regions on the planet. This means it's even more likely that these briny pools are forming elsewhere on Mars. "If we see brines on the equator, there must be brines everywhere on the planet," he said.
Amazingly, Curiosity hasn't been able to capture photographs of Mars's liquid water, because the technology needed to operate a camera (and the Curiosity rover itself) at -100 degrees has not yet been invented. Instead, says Turk, they have to rely on relative measurements of "humidity, air temperature, and ground temperature using the Rover Environmental Monitoring Station (REMS) instrument, and found the results were compatible with the presence of brines at night."
But while liquid water is the key ingredient for life as know it, Martín-Torres told Motherboard that no one should be holding their breath that we're going to find any of that here. "When there are the conditions for liquid water on Mars, those conditions are such that the temperatures are so low that it's not possible for life as we know it to reproduce or to metabolise," he said. Life as we don't know it? Well, never say never.
What this discovery does do is make the prospect of humans living on Mars look slightly more enticing - perhaps Red Planet colonists will be able to somehow harvest this liquid brine at night and filter it down into something useable. We'll just have to wait and see.