If Elon Musk’s Mars colony becomes a reality, he won’t be sending just humans to the Red Planet; he’ll be sending trillions of hitchhiking microbes as well. Such a biological invasion seemingly clashes with a concept known as planetary protection — avoiding the "harmful contamination" of other worlds. Given the likelihood of a human colony to spread microbes, does that put a stop to Musk’s Mars ambitions?

A human settlement isn’t incompatible with planetary protection

Not exactly. A human settlement isn’t incompatible with planetary protection. In fact, those who came up with the concept did so with future Mars settlements in mind. "It was fully recognized that humans could potentially colonize Mars in the future," Catherine Conley, NASA’s planetary protection officer, tells The Verge.

Right now, planetary protection guidelines of Mars have revolved around robotic missions — the only types of missions to go to the planet. Those policies, developed by the Committee on Space Research (COSPAR), are strict since we’re not done exploring the world and determining whether biological life exists there. Rovers need to be sterilized, and extra precautions need to be taken if spacecraft go to Mars' "special regions" — places where organisms may be able to grow. The goal is to not contaminate the planet with Earth life so that we can study it in its natural state.

The planetary protection guidelines for a Mars colony will differ from the ones that are in place now, Conley explains. Rovers and spacecraft can be (mostly) sterilized; people can’t. The human body alone carries more than 10,000 different types of bacteria. So scientists all over the world will have to discuss what makes sense for a human settlement, says Conley. Those guidelines will likely be focused on ensuring human settlers don’t bring anything with them that can harm the colony — and that they don’t send back anything that could potentially harm Earth.

Finding life — and keeping us safe

The legal basis for planetary protection can be found in the Outer Space Treaty — an international agreement from 1967 that has 104 state parties. Article IX of the treaty calls for nations to explore other worlds "so as to avoid their harmful contamination." That’s because astronomers were interested in looking for alien life. If we contaminate Mars and other planets with Earth’s microbes, it’ll make it a lot harder to know if we’re encountering new life, or just what we brought with us.

The signing of the Outer Space Treaty. (UN)

But another major motivation for planetary protection was to protect humans, Conley says. It’s important to explore Mars in its natural state, so we’ll understand the planet’s environment — in case people live there someday. "Understand the environment well enough so you don’t encounter bad surprises," says Conley. The problem is, the existence of life on the Red Planet is still an open question. Data gathered from the Viking landers — two Martian spacecraft equipped with astrobiology experiments — is considered inconclusive. And recent revelations about Mars, such as the presence of flowing liquid water, have raised the possibility that microbes may be able to thrive on the planet’s surface.

"Understand the environment well enough so you don’t encounter bad surprises."

"Maybe there was once something living there" Bill Nye, CEO of the Planetary Society, tells The Verge. "So hey people, let’s go have a look before we land with a bunch of humans." Plus, if we settle a colony of people on Mars without fully knowing what’s there, it’s possible people will encounter some lethal Martian pathogen that we have yet to discover. That’s why Conley and Nye argue it’s prudent to learn more about Mars before we start sending humans there.

Images of recurring slope lineae on Mars, where liquid water is thought to exist. (NASA)

Musk said he isn’t too worried about encountering Martian life, since all signs seem to point to the planet being a dead world. "So far, we’re really not seeing any sign of surface life on Mars. There’s really nothing on the surface of Mars," he argued at a press conference after his speech last week. However, SpaceX has said before that planetary protection is an important subject for the company. "SpaceX takes planetary protection very seriously," Dex Torricke-Barton, the company’s head of communications, said in a statement to The Washington Post. "We are working with NASA to develop and implement stringent procedures. These will first be used for our Red Dragon missions, beginning in 2018."

But in the same statement, Torricke-Barton hinted that nothing should slow us down from sending people to Mars. "If we care about preserving life, we should take steps to safeguard not only microbial life that might exist but also human life that certainly does — and is ready to reach for a new world."

Planetary protection for a Mars colony

So what would planetary protection look like for a human Mars colony? The guidelines will be a bit like brushing your teeth, says Conley. "You can’t keep your mouth totally sterile after eating a candy bar. Brushing reduces bacteria but doesn’t get rid of them," she says. "So we will not be able to keep everything pristinely clean; we’ll allow greater contamination with the expectation of greater benefit."

The guidelines will be a bit like brushing your teeth

The main focus will be limiting the transfer of harmful pathogens to the Martian surface. For instance, if Mars does turn out to be hospitable to Earth microbes, colonists don’t want to bring any harmful organisms over that could survive and cause people grief later on. Deadly bacteria like anthrax or tetanus may actually be able to survive in the Martian soil. "You don’t want to park human pathogens in a place where later on someone’s going to blunder into them," John Rummel, an astrobiologist at East Carolina University and NASA’s former planetary protection officer, tells The Verge. "It would be an uncomfortable discovery that we’ve actually introduced things on Mars when we could have avoided it." COSPAR suggests that future human settlers should still be restricted from contaminating Mars' "special regions" and that robots should survey unexplored Martian sites before people go there.

An artistic rendering of SpaceX's Mars spaceship. (SpaceX)

There will also be guidelines about what colonists bring back with them to Earth. That’s because planetary protection doesn’t just cover the harmful contamination of other worlds in our Solar System. It also entails protecting the Earth from any hazardous material that could be lurking on other worlds. And since Musk indicated that his vehicles would return from Mars and potentially bring people home, guidelines will need to be put in place to ensure no toxic Martian microbes make the return trips as well.

It will take a lot of discussion — among the US government agencies and the nations of the Outer Space Treaty — to figure out what these guidelines should be, says Conley. But something similar happened with the Apollo missions in the 1960s. When those launches happened, the science community wasn’t sure if the Moon had any hazardous material, so restrictions were put in place as to what the astronauts could bring to the Moon and what they could bring back.

"If the US does not engage in international consultation, it could be held liable under international court."

"The same kinds of discussions need to happen again," says Conley. In fact, the US could be in trouble if it doesn’t consult with its international partners about the proper planetary protection guidelines for a Martian colony. "If the US does not engage in international consultation, it could be held liable under international court," says Conley.

SpaceX though is a private company, and currently the US doesn’t have any legal framework to make sure the company adheres to the Outer Space Treaty. Spaceflight company Moon Express encountered this regulatory conundrum when it sought approval for the launch of its lunar lander. The company had to come up with its own "regulatory patch," giving the US government enough comfort that its lunar mission would adhere to the treaty.

Fortunately, lawmakers are working on frameworks that would allow the federal government to oversee private missions beyond lower Earth orbit. Congressman Jim Bridenstine (R-OK), for instance, has come up with a bill called the American Space Renaissance Act, which would give the Federal Aviation Administration the authority to issue guidelines for private missions to other worlds. Once a regulatory solution is put in place, SpaceX will be in a better position to make its Mars colony a reality. And then, many consultations about planetary protection could be in the company’s future.

"It’s so important to have discussions and come to a consensus before we do something we can’t take back," says Conley. "If we contaminate Mars, then we can’t stop that."