Astronomers are fairly sure that Mars was once wet. “Modern Mars, though, is a freezing desert.” In the 4.5 billion years since it came into existence, it’s dried up. As it lost most of its atmosphere, it got very cold, and the bulk of its primeval water boiled away into space. The rest seeped underground, and froze.
But new findings from NASA’s Mars Reconnaissance Orbiter indicate that liquid water flows intermittently even today.
Researchers have detected enigmatic narrow streaks in several locations on the Red Planet, which appear to ebb and flow with the seasons. They darken during the summers, and glide down slopes. These downhill flows, known as “recurring slope lineae” (or R.S.L.s), are thought to be caused by the flow of liquid brine. In winter, when that brine freezes again, they lighten.
Mars never gets balmy enough for pure water-ice to thaw. These streaks, however, contain minerals called perchlorates, which act as antifreeze. They lower the freezing point of the brine to one, which permits it to stay liquid even when the temperature is as low as minus 94 Fahrenheit. (This is the same action a bag of salt has on snow-laden roads and sidewalks on Earth, turning the ice into puddles.)
The implications of this discovery are huge.
If Martians evolved during their planet’s earlier, wetter phase, the continued presence of water means it is just about possible that a few especially hardy types have survived until the present day—clinging on in dwindling pockets of dampness in the way that some “extremophile” bacteria on Earth are able to live in cold, salty, and arid environments.