Back in April, NASA's Curiosity rover found evidence ofliquid water on Mars. Still, this is no life-friendly oasis: The water is hyper-salty, ultra-cold, and contained in fleeting layers of sludge trapped beneath the red planet's regolith soil. Nonetheless, it completes the trifecta of requirements for Earth-like life. We now know Mars has soil-bound nutrients, a carbon monoxideenergy source for hungry microbes, and liquid water.

The scientists behind the water discovery, including Morten Bo Madsen at the Niels Bohr Institute, say that "finding life on Mars still doesn't look very probable, because it's simply just too cold and/or too dry" on large swaths of the planet. But it certainly looks at least possible that there could be environmental niches, probably connected to one of these [salt-water] brines, where life could thrive."

To Gary King, a microbiologist at Louisiana State University who studies life that survives in extreme environments, this presents humanity with an amazing opportunity. We may never find native Martian microbes, and they may, in fact, be long gone. But because the Red Planet's has that life-friendly trio—the energy sources, nutrients and water—we could grow microbial life there ourselves.

"This could just be my naiveté, but I don't think that it's entirely farfetched."

According to King, seeding hand-picked, specially cultivated microbial communities in Mars' harsh environment is not only possible, but could serve as our very first step in terraforming the planet: transforming our solar neighbor from a desolate hellscape to a thriving environment that could support increasing complex forms of life, and possibly one day even humans.

King is clear about the difficulties and caveats such a theoretical project would entail. But that doesn't stop him from believing it's possible.

"This could just be my naiveté, I don't think that it's entirely farfetched to imagine us developing something like a microbial farm on Mars," he says, "and not in something like 200 years, but far sooner."

How it begins

Mars Pathfinder

The concept starts small. Microorganisms that munch on Mars's natural resources could not only transform the red planet's soil, but could pump out gasses to bolster the Mars's embarrassingly thin atmosphere to boot. This is not simply theoretical. Such a process has already been proven already in Earth's history, King says. We owe allour planet's atmospheric oxygen to microbe photosynthesis.

The bigger question is, why? Why the heck we would even want to seed Mars with Earth bacteria and other microorganisms? What could we possibly gain?

All those atmospheric changes the bacteria begin could serve a few purposes. First, it would insulate the planet due to a greenhouse effect—both warming it up and making liquid water more widely available. And "over the long term, a different atmospheric composition could be more suitable for a wider range of life than the current atmosphere could support," King says. Like a series of scaffolds, each generation of new terraforming microorganisms could make Mars more suitable for the next wave of life. And for future (human) Mars colonists, this terraforming could not only make the Red Planet more habitable, but a colony more sustainable and independent from Earth.

Right place

If we want to grow life in the watery-subsurface of Mars, King says, the opening move is identifying the right spot to start. The scant amount of subsurface water recently discovered does not suddenly transform Mars into a fertile Eden. However, "there's no reason to suspect that the entirety of the planet is effectively sterile—that Mars is so limiting, and so extreme, that it can't support any microbial life anywhere," King says. On Earth, King adds, no matter how extreme an environment ("from the dry Atacama desert to geothermal vents under the Atlantic," he says) lifealmost always finds a way.

As for finding the most potentially habitable spot, "that's a task which I think basically continues to come down to a question of water," King says. In other words, wherever Mars's subsurface water pools the most, that's where we'll want to start.

"There's no reason to suspect that the entirety of the planet is effectively sterile."

Granted, the Martian water supply seems to be scarce at best, but it's possible that places like the recurring slope lineae might be our wettest, best bet. This is a swath of land identified in 2011 by the Mars Reconnaissance Orbiter that visibly darkens with the seasons, suggesting that subsurface water there may ebb and flow in much greater amounts than was found in the Gale crater (where the evidence of liquid water was found last month).

With our rovers, orbiters, and various other planned planetary surveying missions, we've already started looking for our perfect niche.

Right organisms

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It's clear that Mars presents any first-generation microbe with a slew of major challenges, including (but certainly not limited to): extremely limited amounts of hyper-salty liquid water, incredibly cold and radically swinging temperatures, and little protection from the harsh radiation of space. According to King, though, we've already found microbes on Earth that can tackle (at least individually) every curveball Mars could throw, from radiation resistance to the ability to survive long (even multi-year) stretches in a deep-freeze.

"What varies is the degree of tolerance," he says, "but there is absolutely enormous metabolic and biochemical potential that already exists in microbes everywhere on Earth."

First, and perhaps most obviously, we'd have to identify microbes with the skills that seem to best match this grand Martian challenge. These are microbes like Alkalilimnicola ehrlichii, which could consume the atmospheric carbon monoxide that seeps into Mars's soil—the only readily available source of energy. "We'll want microbes that can reduce the nitrate and perchlorate in Mars's regolith," making the planet more habitable for future microbes, King says. We'll also want microbes that produce greenhouse gasses to bolster the atmosphere.

Second, it's unlikely that even the heartiest of Earth microbes will be precisely suited to the Mars ecosystem, so we'll need to genetically tweak our first generation of microbe colonizers. "While we certainly want to rely on what already exists in nature, at the same time synthetic biology has given us a remarkable toolkit that can be used to manufacture new kinds of organisms specially suited for the systems we want to plan for," King says. To oversimplify it: we'll want to investigate our chosen microbes, find the genes that code for the survival and terraforming properties that we want (like radiation and drought resistance), and then use that knowledge to genetically engineer specifically Martian-designed microbes.

"Synthetic biology has given us a remarkable toolkit ... to manufacture new kinds of organisms."

This is the biggest bottleneck of the project, King admits: Our terraforming aspirations are totally grounded until we're sure we can genetically tweak and tailor the right microbes. That's a hurdle that's maybe a decade or more away, he thinks.

Lastly, King says, we'll want to develop not a single kind microbe but a suite of several that work together. A variety of microbes could share the complicated burden of terraforming, and a flexible ecosystem of many microbes could help all the microbes survive: In harsh Earth climates like salt-flats or thermal vents, King says, we find that hardy microbes rarely exist on their own. They form a complex community to get by.

A little push

NASA

When we spoke to King, he was on Hawaii's Kauai island studying how a first generation of microbes settle on and inhabit a sterile environment—in this case, lava rock freshly cooled after a volcanic flow. On Kauai, airborne microbes simply fall from the air and dig in their heels. On Mars, Humans will have to give our terraforming Martian microbes much more help and attention.

King says we may want to kickstart our microbes with an initial chemical dump of "freon, sulfur hexafluoride, or some other gases that we know are very, very potent greenhouse gases here on Earth. This initial atmospheric introduction could start raising temperatures and increase water availability," he says, possibly giving microbial life the critical edge it will need.

According to King, the astounding variability of our current Martian rovers, Curiosity and Opportunity, shows that we could use much machines to tend to our first Martian microbes. "One could image a crew of rover farmers tending a microbial crop, operating out of a nearby base," he says.

"One could image a crew of rover farmers tending a microbial crop."

Deal-breakers?

Even if we threw everything we've got into a huge microbial terraforming project, King says, Mars will never be quite like Earth in two unavoidable ways. First, Mars' gravity is 62 percent lower. That's not a deal-breaker, necessarily. Scientists don't expect that lower gravity would prohibit the long-term existence of large, multicellular Earth-like life.

But there's a bigger issue. No amount of biological terraforming will bring back Mars's lost magnetic field—the protective shield that, on Earth, is caused by our convecting metallic core. Can we grow microbes? Maybe. But with no way to story the deadly space radiation that our own planet's magnetosphere filters out, it's hard to image large lifeforms—say, us— ever living on Mars without it (unless you're aiming for the Total Recall life-in-a-dome-method).

There's something else that could tank any hope of terraforming Mars: If we ever found native, living organisms on Mars first. "Yes, that would raise a very tough discussion of ethics," King says. "It's much easier to think about introducing life if you know you're not destroying anything."

Worth the thought

To be sure, using microbes to terraform Mars is a speculative idea. But even if such a project is far, far off, both King and Morten Bo Madsen—the planetary scientist involved in the recent Mars liquid water discovery—agree that it's more than a mere thought experiment. Big ideas give birth to something real.

"In science, these types of wild ideas and speculation are good," Madsen says. "I think this concept of pushing ideas like this to the extreme and seeing what you can get—this is where scientific progress comes from," he says.

Even if we wanted to terraform Mars, King concedes, science may not yet have all the tools needed to change Mars' environment on a planetary scale (we're looking at you, genetic engineering). But even if that's true, he argues, working on the project could have benefits right here at home.

"In science, these types of wild ideas and speculation are good."

"The knowledge that we'd gain from attempting or even just studying this type of massive experiment would certainly help us in understanding how we could be managing our own planet, something we've been doing since the industrial revolution and still haven't come to grips with."

Or, as superstar physicist Neil deGrasse Tyson recently said in an interview with PM: "If you have the power of geoengineering to turn Mars into Earth, you have the power of geoengineering to turn Earth back into Earth."

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