In just the last few months, we’ve learned of new evidence that complex organic molecules—ostensibly the constituent ingredients for life—have been preserved in Martian rocks; that Mars’ atmosphere exhibits seasonal variations of methane, a potential chemical signature of life; and that a huge reservoir of liquid water exists under the surface of the planet itself.
Each of those discoveries thickens the plot in the search for extraterrestrial organisms and teases us into believing we might soon find the first evidence ever that life elsewhere exists.
And while signs of alien life that lived long ago would be groundbreaking, the bigger question people have is: What does Mars mean for the future of life as we know it?
“If life ever started on Mars, it’s probably still there.”
— Nathalie Cabrol, NASA astrobiologist
Life on Mars would be a brilliant thing to witness. It would be a mistake, however, to presume this past summer’s news means we’re likely to see something of that scale unfold.
Those reasons start with the fact that the 4.6 billion year history of Mars is a complicated, tragic tale.
Ancient Mars was a much different planet from its current form. In fact, it was similar to Earth. It was brimming with a thick atmosphere that kept things warmer, protected by a magnetic field that could stop cosmic radiation and UV rays from sterilizing the surface, and almost certainly teeming with vast bodies of liquid water on the surface of the planet that could support life as we know it.
“There’s not a consensus, but there’s a general expectation [ancient] Mars must have been looking like a good summer Arctic day,” Nathalie Cabrol, a NASA astrobiologist who is extensively involved with the search for signs of extraterrestrials on Mars, told The Daily Beast.
For life to exist, “you need energy, you need water, you need nutrients, and you need a shelter, and you have all of these on an early Mars. If you want a time where life could have started, early Mars would have been the time.”
That’s a far cry from what Mars looks like today. Even under the most ideal conditions, like a summer’s day, Mars temperatures might tick up to nearly 70 degrees Fahrenheit.
But at night, temperatures plummet down to lower than -100 degrees. That’s not even considering how much colder things are near the poles or during the winter months. There’s no strong atmosphere to keep the climate warm and temperate for humans. And Mars lost its magnetic field a long time ago, which means radiation would zap anything that’s hanging around on the surface anyway.
“I always compare this to cuisine,” Cabrol said. “You have ingredients on the table. Two people can take those ingredients and get the same results. But if one is a great chef and one doesn’t know anything about cooking, you will end up with two very different things.”
Those two sets of hands in the kitchen are Earth and Mars, respectively. And while Earth whipped up a dish of biological delights, Mars may have barely made something edible, if it even managed that.
Three months ago, the Curiosity Rover stumbled upon a three-mile high mountain—the Gale crater—near the Martian equator with a valley that seemed to contain methane, a sign of primitive, organic life.
But researchers restrained their excitement, because of the structure of the organics themselves.
“The chemical structure [of the molecules], as far as we understand, is rather random,” said Roger Everett Summons, an MIT researcher of planetary science and a member of the team that made the Gale crater discovery.
They are, chemically speaking, the buildings blocks of life, but they lack the sort of organization that actually allows them to be constructed into life. It’s a bit like seeing concrete cut into fine blocks, versus seeing concrete that’s just cut into any sort of odd shape you can think of.
“The fact that [these organics are] still there after millions of years of radiation—cosmic rays and UV—says something about the stability of those materials,” said Summons. “But it doesn’t say anything about the origins.”
Summons believes the organic molecules, due to their structure, weren’t formed on Mars, but instead came to the red planet aboard meteorites.
Dirk Schulze-Makuch, a German astrobiologist and a professor at the Technical University of Berlin, interprets the structure of the organics differently, and believes they could be signs of past alien life.
“The fact that [these organics are] still there after millions of years of radiation—cosmic rays and UV—says something about the stability of those materials.”
— Roger Everett Summons, MIT researcher of planetary science
But he also notes that they show signs of degradation. “It’s not going in the opposite direction, the direction toward life,” he said. “It’s going in the direction of decay of becoming destroyed. It would make more sense for the molecules to have once been a part of organisms, or less likely, from meteorites from space. But they won’t evolve into life.”
Even if conditions on Mars were to change into something more favorable—say, humans come down and terraform the red planet into Earth 2.0—Schulze-Makuch still doubts the molecules possess the chemistry to come together and create biology.
“Even in current Earth conditions, I don’t think we’d be able to see any origins of life,” he said. “Oxygen would right away oxidize organic molecules. On Mars it’s the same way—the [cosmic] radiation would readily oxidize molecules, so we wouldn’t get the correct synthesis reaction. I don’t see any realistic scenario on Mars where this could happen.”
Caroline Freissinet, a scientist with the Atmospheres Laboratory (LATMOS) for the French National Center for Scientific Research and another member of the Gale crater team, also pointed out that even if all the aforementioned problems didn’t exist, there’s still a key reason why these molecules would not work in the creation of new Martian life: There’s not enough of them on the planet.
“One could touch the soil on the surface of the Earth and find more organic matter on their finger there than what is on Mars right now that we’ve discovered,” she said.
Ultimately, the best chances for future life on Mars is the fact that it has already survived the last several billion years here on Earth.
“We know from Earth that life is like a disease,” said Cabrol. “It’s really really hard to get rid of it! It would not have been too difficult for life to continue surviving on the surface of Mars. If life ever started on Mars, it’s probably still there.”
So what would that life look like today on Mars? Cabrol has spent much of her research in the field, exploring some of the harshest, coldest places on Earth to study the scant microbes, called extremophiles, that have managed to live on in these places. These environments are the closest analogues we have to conditions on Mars.
“Whenever you think you have figured it out, life finds a way to surprise you and be in places you would not expect it to be.”
— Nathalie Cabrol, NASA astrobiologist
She thinks endoliths, extremophiles that live in clays in porous rocks, are most like what we might find on Mars, if there’s something still there.
The subglacial liquid water reserve near the south pole is one potential habitat where we might stumble upon Martian life. But there is reason to be skeptical. The water has likely escaped a frozen fate by interacting with hyperchlorates, turning the water extremely salty. Some extremophile might have learned to adapt to these conditions, but Freissinet pointed out that “life keeps surprising us.”
According to Cabrol, if there’s a source of energy near the water that could sustain potential life, like volcanic heat, there’s hope of finding something down there.
“Life 1.5 kilometers under the surface absolutely doesn’t care what’s happening at the surface,” she said. “Climate change on the surface doesn’t matter.”
If life does exist on Mars, we would almost certainly have to dig hundreds or even thousands of feet deep into all the red rock to find it. Stumbling on it from the surface seems quite unlikely, and even less likely is the idea that, no matter what we did to the planet, life could (re)emerge of its own accord.
But unlikelihood doesn’t mean it’s wise to write it off as a possibility—we could see Martian life evolve one day.
“At this point there’s no way we can definitively say life can or cannot evolve on Mars,” said Cabrol. “Whenever you think you have figured it out, life finds a way to surprise you and be in places you would not expect it to be.”