This Humble Plant Species May Be the Key to Terraforming Mars

Watch out, tardigrades: The first life form to colonize Mars may be a hardy desert moss, according to a recent study.

A team of researchers recently put a desert moss called Syntrichia caninervis through a barrage of tests, from years in a deep freeze to blasts of gamma and ultraviolet radiation, in a simulated version of Mars’s thin, mostly-carbon dioxide atmosphere. And the moss survived it all. According to the study, that means S. caninervis, also called steppe screw moss, may eventually be able to grow on Mars — and even help terraform the cold, dry planet.

“S. caninervis represents a promising candidate as a colonist to facilitate terraforming efforts on Mars or other planets,” write Chinese Academy of Sciences ecologist Xiaoshuang Li and his colleagues, who published their work in the journal The Innovation.

Surviving on (Simulated) Mars

After spending up to 5 years in deep deep freezers at -112 degrees Fahrenheit for up to 5 years, most plants would be dead, but when Li and his colleagues thawed out their samples of S. caninervis, the moss recovered within a few days and even grew new branches. Li and his colleagues blasted other samples with 500 grays (units of ionizing radiation) of gamma radiation. This is about ten times higher than the dose required to kill humans pretty much immediately. The moss not only survived, but thrived: Radiation-blasted samples grew more new branches than control samples. Sort of like the Hulk, if Bruce Banner were a tiny plant.

Scientists have spent decades looking for organisms that could survive in the vacuum of space or on the surface of Mars for decades now – and trying to figure out how they do it. Bacteria, spores from fungi and plants, and even the iconic tardigrade (reigning champion of surviving horrible conditions) have spent weeks at a time exposed to the vacuum of space (meaning no air or pressure) in experiments on the outside of the International Space Station, for example. But Li and his colleagues’ experiments are the first time a whole plant has survived anything like conditions on the surface of Mars.

That means surviving with little or no air – or at least what we humans think of as air. Almost all the air on Mars is actually carbon dioxide, which we can’t breathe, but plants can. On the other hand, Mars’s atmosphere is extremely thin; on the ground, Martian air pressure is only about 1 percent of the air pressure at sea level here on Earth. You don’t think about the weight of the whole atmosphere pressing down on you very often, but without it, liquid water would boil into steam in an instant (which would be very unpleasant for you, a creature made of about two-thirds water).

Surviving Mars also means being bombarded with radiation, because the thin Martian atmosphere doesn’t offer much protection from ultraviolet or gamma rays. It also means enduring intense cold, down to about -70 degrees Fahrenheit. Li and his colleagues put some S. caninervis in a tank that simulated those conditions for about a week, and afterwards, the moss recovered and grew again.

Here on Earth, S. caninervis lives in some of the coldest and driest places on Earth, like Tibet, Antarctica, and the Arctic Circle. That’s why Li and his colleagues thought it might be a good candidate to help Earth life gain a green foothold on Mars – and turn the planet into a livable place.

“S. caninervis can help drive the atmospheric, geological, and ecological processes required for other higher plants and animals while facilitating the creation of new habitable environments conducive to long-term human settlement,” write Li and his colleagues.

And there’s good reason to imagine moss as a future terraformer, because the first plants to colonize land here on Earth were mosses.

Surviving but Not Thriving — Yet

The moss rebounded from everything Li and his colleagues simulated Mars could throw at it, but there are a couple of slight catches. As Li and his colleagues acknowledge, “there is still a long way to go to create self-sufficient habitats on other planets.”

First, don’t picture a green, fluffy carpet of moss, happily living its best mossy life in freezing temperatures with no water. Instead, picture a clump of dried-out brown moss, waiting patiently until the weather turns warmer and nearby ice melts enough to sprinkle it with water. S. caninervis, like many other mosses, can force most of the water out of its cells to wait out freezes, droughts, and even bursts of high-energy radiation. When the moss senses nearby water and a comfier environment, it can regenerate and start growing again.

That means that if we planted a patch of S. caninervis somewhere on Mars, it would pretty much just sit there and look dead until we found a way to water it without the water immediately boiling away in Mars’s thin atmosphere. But it’s a start.

Li and his colleagues also noticed that moss samples recovered faster if they’d been dried out before being hit with the deep freeze and radiation tests, although even moss that started out without that advantage did recover.

What’s Next?

“Looking to the future, we expect that this promising moss could be brought to Mars or the Moon to further test the possibility of plant colonization and growth in outer space,” write Li and his colleagues.

Of course, that’s fraught territory, since at the moment we’re still trying to figure out whether Mars was ever home to life of its own. Contaminating the place with Earth life, especially Earth life that might actually survive there, is high on the list of things most space agencies want to avoid for the foreseeable future. Any mission that eventually does take moss — or any other living samples — to Mars is probably going to have strict protocols to follow to keep from giving the planet any Earth cooties.

Meanwhile, though, the Moon might be a better place, since it was never home to life of its own and it’s unlikely anything could actually gain a foothold there. And moss samples on the Moon would at least have some tardigrades for company.