Mars is a very different world from ours. While evidence continues to mount that early Mars had lots of water, and possibly even oceans on its surface, it’s been dry for at least a billion years.
As the planet transitioned to a cold, arid world, chemicals such as hydrogen peroxide and perchlorate accumulated on its surface and subsurface. If any life exists on Mars today, it would have had to adapt to the presence of these biology-unfriendly compounds.
In a new paper published in the journal Astrobiology, Jacob Heinz from the Technical University of Berlin and colleagues (including myself) report just how much chloride and perchlorate Earth microorganisms can tolerate, and how they adapt to the presence of these chemicals. The tests were done with a microbe, Planococcus halocryophilus, that thrives in the cold and salty environment of the High Canadian Arctic. After exposing it to higher and higher perchlorate and chloride concentrations at different temperatures, the scientists found that P. halocryophilus exhibits the highest tolerance to sodium perchlorate of all microorganisms tested so far.
This is not to say terrestrial microbes could survive in an underground Martian lake like the one described by Roberto Orosei and his Italian colleagues last year. That lake, which was discovered by radar measurements from Martian orbit, has a temperature of about -68o C, and therefore must have extremely high concentrations of perchlorate to keep its water liquid.
That’s too much of a challenge for P. halocryophilus, it seems. However, the survivability gap may be closing. Heinz also found a fungus that can grow at even higher concentrations of sodium perchlorate—up to 20 percent. And for other tested chemicals, such as calcium chloride, higher concentrations can be tolerated by microbes at lower temperatures.
It makes sense that if Martian microbes were exposed for long periods to high concentrations of what we consider toxic chemicals, they might adapt to them better than Earth organisms have. Ours is an ocean planet, after all, and there are very few places on Earth where an adaptation to perchlorates would be useful.
So stay tuned.