Mars has water. Not just ice and snow, but liquid, flowing water. It’s salty and scant, but water is one of the essential ingredients for life on Earth—and although the Red Planet certainly wouldn’t be a cushy place to live, scientists think there’s a chance that single-celled organisms could be lurking somewhere on Mars. If we want to find it, we need to look in the places where it’s most likely to be; according to NASA, we need to “follow the water.”

Trouble is, most Mars spacecraft aren’t allowed to “follow the water,” because they’re not clean enough to enter the warm, wet “Special Regions” where Martian life is most likely to have gained a foothold. (Special Regions are defined by the International Council for Science’s Committee on Space Research, under their planetary protection policies.) The logic is that if we send a dirty spacecraft into one of these Special Regions, Earth microbes could also thrive there, contaminating Mars and making it so that if we ever do discover microbial life on Mars, we won’t know whether it’s native to Mars or imported from Earth.

Our spacecraft aren’t clean enough to safely enter the “Special Regions” where Martian life is most likely to be.

If NASA is serious about sending astronauts to the Red Planet in the 2030s, then it’s important to get a yes or no answer to this age-old question before humans drop in and make a mess. Yes, we’ve probably already contaminated Mars to some extent with our previous spacecraft, but humans are a lot harder to sterilize than machines.

“Once we send humans to Mars, it will be really, really hard to avoid contamination,” says Nilton Renno, an engineer and astrobiologist at the University of Michigan. “Humans would take a huge number of microbes with them. They would leak out of a spacecraft and some of them would potentially end up in Special Regions because of transport by wind.” Plus, he adds, “if humans go to Mars, they would want to explore the most interesting regions”–like the ones with water in them.

Currently, the only planned mission capable of letting us test for life before astronauts arrive in the 2030s is the Mars 2020 rover, and it cannot be sterilized thoroughly enough to enter the areas where Martian life is most likely to be lurking.

Shouldn’t We Have Found It By Now?

In the 1970s, the twin Viking landers were the first NASA spacecraft to touch down on Mars, and the first to test for life there. The answer they sent back was a very anticlimactic “maybe”. One of the tests found evidence for metabolic activity, but the others didn’t find organic materials—the stuff that living things on Earth are built from.

As the “Mars has life” headlines faded, a 15-year hiatus in Mars exploration followed in Viking’s wake; taxpayers don’t like spending money on inconclusive experiments.

When NASA finally did resume Mars exploration, they took a less direct approach—instead of looking for life, spacecraft began searching for conditions that could be right for life, either in the past or present. The Curiosity rover’s goal, for example, is to “assess whether Mars ever had an environment able to support small life forms called microbes.”


View from Viking lander 1

In the 1970s, the Viking landers searched for life on Mars, but the results were inconclusive.

In 2011, a team of scientists suggested that maybe Viking actually did detect organic material on Mars. NASA, having never been to Mars before, didn’t realize that the Martian soil is rich in perchlorates, which break down organics. The team asserts that the remnants of organic materials, which were disregarded as Earthly contaminants, were actually the cremated remains of Martian organics. That’s no guarantee of life on Mars, but if organics are there, they would seem to increase the chances that life could be there too.

Make no mistake: Mars is a harsh place. It’s cold, and perpetually zapped by harmful radiation. Yet there’s promising chemistry in Martian soil that suggests microbial organisms would have food to munch on, and water ice is present at the poles and underground. On Earth, virtually everywhere there’s water, there’s life.

“Harmful Contamination”

When the U.S. signed the Outer Space Treaty in 1967, we agreed that when exploring the Moon and other celestial bodies, we would “avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter”.

The phrase “avoid harmful contamination” is open to interpretation. We don’t know whether there’s life on Mars, or how our microbes could potentially impact it.

“If we don’t have the information, we won’t know the consequences.”

International science organizations have decided that testing for life on Mars is not an absolute precondition for sending astronauts, but it’s a good idea. “There has not been a consensus as to whether we should,” says Catharine Conley, a planetary protection officer at NASA.

If there is life on Mars and we don’t know it, we could put Martian life at risk from our own biology—on Earth, moving a species from one region to another can cause disastrous results. What happens if we accidentally introduce an invasive species across interplanetary space? Conversely, Martian life could also endanger Earth and/or the health of our astronauts.

“If we don’t have the information, we won’t know the consequences,” says Conley. “It’s safer to explore places when you know more about them.”

Stringent Requirements

The Viking mission set the standard for spacecraft cleanliness. At the time, scientists expected to find life on Mars, so the landers were disinfected and baked at up to 260 degrees Fahrenheit for long periods of time, getting the spore count down to 30. Future spacecraft with the goal of testing for life would also need to go through that baking process–which means they have to be designed to withstand oven temperatures.

Today, before a spacecraft goes into space, it faces a battery of sterilization techniques, including chemical assault and UV rays. Even still, a rover like Curiosity is allowed to launch carrying as many as 300,000 bacterial hitchhikers. In order to make a spacecraft clean enough to enter one of Mars’ Special Regions, the team would need to get that number down to 30. That can be prohibitively expensive and time-consuming. (Some researchers have argued that the strict standards are overcautious, to the detriment of Mars exploration.)

Sterilizing spacecraft thoroughly enough to enter a Special Region would add significantly to a mission’s cost. About a decade ago, NASA and the European Space Agency (ESA) concluded that it would cost about $100 million to retrofit the Mars Exploration rovers Spirit and Opportunity with heat-resistant materials, to enable them to survive the heat-sterilization that’s a prerequisite to going in search of alien life. Conley says the process would be a bit cheaper for projects that are designed for ultra-sterilization from the start.

“It has to be cleaned throughout the life of the spacecraft,” says Renno, from the time the engineers begin putting it together in the cleanroom, to the time it’s strapped to the rocket that launches it. And even the rocket has to be decontaminated. “You have to make sure that everything from the lab all the way to Mars is clean.”



The ExoMars rover will carry a drill and life-detection equipment, but it won’t be able to travel into the areas where life is most likely to be lurking on Mars.

ESA’s ExoMars rover will land on Mars in 2018 to search for biomarkers that could indicate past or present life. The Mars 2020 rover launches in five years, with plans to collect samples of Martian soil that can be picked up later by an undefined mission that will bring the samples back to Earth, so scientists can test for life. However, neither ExoMars nor Mars 2020 will be clean enough to travel into a Special Region, and it is too late to upgrade them now.

“The thing that you can never replace is time,” says Conley. And retrofitting has another disadvantage: “When you change things, they don’t necessarily work the way they did before.”

So the results these spacecraft return will likely be inconclusive; a detection of Martian life could be a false positive caused by Earthly contaminants, while a negative finding doesn’t mean much since we didn’t check the places where life is most likely to be.

“It seems pointless to send missions to search for life into non-Special regions if the Special regions are the regions that are of interest for possible life,” says NASA planetary scientist Chris McKay.

Renno agrees. “If we’re looking for life, we should really go where life is most likely to be.”

Better Alternatives

NASA has no life-detection mission currently planned for launch—not one that would go into a Special Region anyway. Luckily, there’s still time to give it a shot before humans are supposed to arrive in the 2030s.

“It is actually not that hard to send missions to a Special Region,” says McKay. “There are special requirements and they have to be designed into the mission.”

One proposed mission is Icebreaker, which would drill into Mars’ north pole, where ice could be preserving the remains of ancient life. Led by McKay, the mission would be designed from the start to be sterilized thoroughly enough to search for life in Special Regions. If selected for funding, it could launch as early as 2020 for a cost of $450 million, plus launch costs.

Another BOLD proposal, the “Biological Oxidant and Life Detection” mission, would send six small probes to Mars to look for life. When the mission was proposed a few years ago, researchers estimated it could launch as early as 2018 and could cost less than $300 million, though they didn’t specify as to whether these spacecraft would be cleared to enter Special Regions.



Icebreaker’s drill has been tested in icy Arctic and Antarctic soils.

It’s certainly possible to design spacecraft with modern materials that can withstand baking during sterilization procedures, says Conley. Many military electronics are required to operate at temperatures at or higher than Viking had to withstand in the cleanroom. Still, the process requires a lot of care, since materials can expand or contract, or even break under extreme heat.

And of course, designing spacecraft components is just one part of organizing a life-detection mission. Funding will also be an issue, with NASA’s dwindling budget.

What may prove to be even trickier is deciding what’s the best way to test for life—should we look for DNA-based life, for example, or would Martian life be entirely different from our own biology?—as well as interpreting the data we get back. Scientists are still debating whether the Viking landers detected life on Mars back in 1976. If we want to send astronauts to Mars in the 2030s, we can’t spend another 40 years arguing.


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