The search for life on Mars just got a lot more interesting. The odds are slim that Mars hosts life today. Still, a newly spotted lake near the Red Planet’s south pole ups the chances that scientists could find microbes living on Mars today.
For decades, when scientists looked at the dry and dusty planet, they focused on sites that might have supported life when Mars was warmer and wetter. But on July 25, researchers announced finding signs of a large lake of liquid water. It appears to be hiding beneath thick layers of ice near the Red Planet’s south pole. And it could provide a reservoir for salt-adapted organisms.
The increased possibility of life also changes the strategy of astrobiologists. They want to protect any existing extraterrestrials from being wiped out or overrun by species hitchhiking in on Earthly spacecraft.
Mars landers and rovers are carefully cleaned to avoid any possible contamination. And that was true even before there appeared to be “anything you’d even call a pond,” says Lisa Pratt. She’s an astrobiologist and NASA’s official planetary protection officer. “Now we have a report of a possible subglacial lake!” That, she notes, is “a major change in the kind of environment we’re trying to protect.”
So how does finding the lake change the quest for life on Mars?
First: Could anything really live in this lake?
It would be a tough territory for most Earthly microbes. Life on Earth fills every niche it can find, from cave crystals and arid deserts to sediments on the deep-ocean floor. But the low temperature cutoff for most life on Earth is around –40° Celsius (-40° Fahrenheit). The Martian ice sheet is about –68 °C (–76 °F). “It’s very cold — colder than any environment on Earth where biologists believe life [can live and reproduce],” Pratt says.
The lake does seem to contain plenty of water. But for the water to be liquid at such cold temperatures, it also must be extremely salty. “On Earth, these kinds of briny mixtures present significant challenges to living organisms,” says Jim Bell. He’s a planetary scientist at Arizona State University in Tempe and president of the Planetary Society.
Some bacteria on Earth seem to thrive even in extreme conditions. But even the so-called “extremophiles” (Ex-TREE-moh-fyles) “that can live in highly salty water might not be able to survive” in the cold, Martian lakes, he says.
But could Martians live there?
“Absolutely,” Pratt says.
If life arose on Mars at some point in its more life-friendly past, some of those organisms might have adapted to the Red Planet’s changing climate. These might have ended up finding the cold, salty water quite comfortable, she says. “This to me looks like an ideal refugia — a place where you could just hang out, maybe be dormant and wait for surface conditions to get better.”
What’s different about this lake versus other watery places where we hope to find life, like Saturn’s moon Enceladus?
For planetary explorers, Mars has one big advantage over the icy moons of Saturn and Jupiter: We’ve landed on it before. Getting to Mars would be a relatively quick journey. A spacecraft could reach there in four to 11 months. And the planet’s atmosphere makes landing much simpler than on the tiny, airless moons.
The big question for planetary protection is whether Mars’ lake has any contact with the planet’s surface. On Saturn’s moon Enceladus and possibly on Jupiter’s moon Europa, liquid water from a subsurface ocean sprays into space from cracks in the ice. Those plumes would make sampling the oceans relatively simple: A spacecraft could just catch some spray during a flyby. But the fact that water can get out also means that invading microbes can get in.
Even though no Mars spacecraft has landed near the suspected lake, global dust storms — like one currently raging on Mars — could carry in contamination from anywhere on the planet.
“So if [the lake is] real, let’s hope there’s no passageway into it,” Pratt says.
If there’s no way in or out, how can we see if anything lives there?
That is a problem. But it’s also not impossible to overcome.
To check the lake for signs of life, “you gotta drill,” explains Isaac Smith. He’s a planetary scientist in Lakewood, Colo., working for the Planetary Science Institute. Scientists have already probed similar under-ice lakes on Earth, such as Lake Whillans in Antarctica. In 2014, a U.S. team drilled through some 1.6 kilometers (1 mile) of ice. Each thimbleful of water they brought up contained roughly 130,000 living cells. In all, this water hosted 3,931 microbial species or groups of species.
Drilling on Mars would be even more technically challenging. It also could face opposition from the scientific community. “Like the subglacial lakes in Antarctica, [the Mars lake] would be considered an extraordinarily rare and special place,” Pratt says. “I expect there would be lots of resistance to drilling into it.”
But if we’re lucky, there could be a sign from above. Scientists have detected signs of seasonal variations in the amount of methane in the Martian atmosphere. This has suggested these variations might point to microbial life under the surface. The European Space Agency’s ExoMars Trace Gas Orbiter, which began taking data in April, is looking for more such methane.
“ExoMars could find a ‘smoking gun,’ so to say,” says Roberto Orosei. This planetary scientist works at the National Institute of Astrophysics in Bologna, Italy. He also was part of the team that just discovered the Martian lake. “Association of liquid water and methane in the atmosphere,” he says, “would be very, very exciting evidence of something going on on Mars.”