Image : NASA

A research team is proposing a major philosophical shift in our thinking about the spread of Earthly microbes in space and on Mars in particular. Believing interplanetary contamination to be “inevitable,” the team argues that future Martian colonists should use microorganisms to reshape the Red Planet—a proposition deemed grossly premature by some experts.


In a paper published last month in FEMS Microbiology Ecology, microbiologist Jose Lopez, a professor at Nova Southeastern University in Florida, along with colleagues W. Raquel Peixoto and Alexandre Rosado from Federal University of Rio de Janeiro, proposed a “major revision” to current philosophies behind space exploration and planetary protection policies as they pertain to the spread of microorganisms in space.

Rather than worry about contaminating foreign celestial bodies—something NASA and other space agencies take great care to avoid—Lopez and his co-authors make the case that we should deliberately send our germs to outer space and that the dissemination of our microbes should be part of a larger colonization strategy to tame the climate on Mars. A key argument proposed by the researchers is that the prevention of contamination is a “near impossibility,” as the authors phrase it in the study.


“Microbial introduction should not be considered accidental but inevitable.”

A change in policy like this would run in stark contrast to conventional thinking on the matter. Some of the experts we spoke to said protocols currently in place to prevent us from contaminating another planet are likely working to the best of our knowledge, and we shouldn’t just give up so easily. What’s more, the experts said plenty of science still needs to be done on Mars and elsewhere before we begin to entertain this unrecoverable possibility.

Currently, the larger scientific community stands in agreement about the need to prevent microbial contamination of planetary bodies like Mars. NASA, ESA, and other space agencies carefully and expensively sterilize their instruments prior to launching them toward neighboring celestial targets.

The philosophy of planetary protection, or PP, dates back to the late 1950s and the establishment of the Committee on Space Research (COSPAR), which was set up by the International Council of Scientific Unions. COSPAR, among other matters, develops recommendations and protocols designed to protect space from our microbes. Relatedly, the UN’s Outer Space Treaty, which has been signed by over 100 nations, specifically states:

States Parties to the Treaty shall pursue studies of outer space, including the moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter and, where necessary, shall adopt appropriate measures for this purpose. If a State Party to the Treaty has reason to believe that an activity or experiment planned by it or its nationals in outer space, including the moon and other celestial bodies, would cause potentially harmful interference with activities of other States Parties in the peaceful exploration and use of outer space, including the moon and other celestial bodies, it shall undertake appropriate international consultations before proceeding with any such activity or experiment.


The primary rationale behind this thinking is that our germs have the potential to contaminate scientifically important places in the solar system, thus spoiling our ability to detect indigenous microbial life on Mars and other worlds. Finding traces of DNA or RNA on Mars, for example, wouldn’t automatically mean they originated from Earth, as these molecules could represent a fundamental and ubiquitous building-block of evolution in the Universe. Perhaps even more problematically, it’s feared that invasive Earthly life could snuff out an alien ecosystem before we even have a chance to study it.

On the other hand, Lopez and his colleagues believe it’ll be next to impossible to prevent our germs from encroaching onto the places we’re exploring, so we might as well have a rational discussion about how to best use microorganisms to our advantage. Specifically, the authors are referring to the prospect of terraforming—the hypothetical practice of geoengineering a planet to make it more like Earth.


Martian surface as seen from space. Image : ESA/DLR/FU Berlin

Looking at Earth’s ancient history as a precedent, the authors acknowledge the critically important role played by microorganisms to foster habitability on our planet, including the production of oxygen, the regulation of gases like carbon dioxide, methane, and nitrogen, and the breaking down of organic and inorganic materials.




“Life as we know it cannot exist without beneficial microorganisms,” said Lopez in an NSU press release. “They are here on our planet and help define symbiotic associations—the living together of multiple organisms to create a greater whole. To survive on a barren (and as far as all voyages to date tell us) sterile planets, we will have to take beneficial microbes with us [to Mars]. This will take time to prepare, discern and we are not advocating a rush to inoculate, but only after rigorous, systematic research on earth.”

Key to their argument is the acknowledgement of our transition from explorers to colonists. That life might exist or have existed elsewhere in the solar system appears not to be the case, the authors claim. The “lack of any discovery or evidence of life from any of the past 70+ space missions and probes which have left Earth’s orbit points to only one unique presence of life in our immediate solar system,” they write.


Lopez and his colleagues contend that, if we’re going to take the colonization of Mars seriously, we’re going to have to consider the role played by our microbes. But spreading germs around Mars is not to be done indiscriminately and without careful foresight, they say.

“Instead, we envision a deliberate and measured program of research into microbial colonization, realizing the limits of current technologies. Thus, we advocate a conservative schedule of microbial introductions into space, while also realizing that human colonization cannot be separate from microbial introductions.”


To that end, the researchers are proposing a Proactive Inoculation Plan, or PIP. Such a plan would be put in place prior to any long-term mission and would involve the screening of promising microbial candidates. Dangerous microbes would be discarded, while only the “most productive” microbes would be included for future missions, as the authors write:

If humanity is seriously contemplating colonizing Mars, another planet or one of the nearby moons in the future, then people need to identify, understand and send the most competitive and beneficial pioneers. Choosing or developing the most durable microbial [species] or communities may be done with deliberation, systematic research and current data, rather than sending random bacteria serendipitously hitchhiking on space stations.


Extremophiles—microbes capable of living in the harshest environments on Earth—would be the first microbes dispersed to Mars, likely buried a few feet underground to protect them from the freezing conditions and radiation on the surface.

But as the authors themselves admit, “total control of a full inventory of microbial [species] and their genomes sent into space can never be realistically achieved,” and the “retrieval of microbes once sent may be impossible.” In other words, we’re never going to have full control or knowledge of the process, nor will we be able to stop it once we start.


The authors offered no specifics in terms of when the first microbes should be planted on Mars, or how long it’ll take for the microorganisms to produce the desired effects—assuming it’ll even work. It’s an open question, for example, if microbes, even extremophiles, can function on the Martian surface where the exceptionally low air pressure hovers around a paltry 0.7 kPa, which is not too far removed from the conditions found in outer space. The low gravity on Mars along with the intense solar radiation hitting the surface complicate the picture even further.

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But even if it does work, the timescales involved should discourage even the most optimistic would-be Martian colonists. On Earth, these processes required hundreds of thousands and possibly millions of years of patient microbial churning (e.g. the production of oxygen via photosynthesis by cyanobacteria).

Bruce Jakosky, a professor of geosciences at the University of Colorado and an expert on the prospect of terraforming Mars, said the authors are proposing some “very dramatic changes” to the world’s planetary protection protocol, as he wrote in an email to Gizmodo.


“These [recommendations] seem to run counter to decades of the approach that we’ve taken to PP,” said Jakosky. “I welcome the opportunity to have further discussion of how PP should be implemented and whether changes should be made to it, but I worry about suggestions that recommend such wholescale changes without thoroughly exploring their consequences with an unbiased view.”

Physicist Todd Huffman from the University of Oxford said the authors committed a fallacy of logic by claiming it’s impossible to completely sterilize a spacecraft on Earth, and so we shouldn’t even try. Huffman believes we should most certainly try and that there’s a very good chance we’re succeeding with our planetary protection schemes, whether that’s thanks to protocols on Earth, the ravaging effects of exposure to deep space, or the harsh conditions already in place on Mars.


As far as we know, the Curiosity rover did not introduce microbes to Mars. Image : NASA

“There have now been quite a few probes that have landed on the surface of Mars since 1976. All of them have been subject, so far, to the extreme sterilization protocols of COSPAR,” wrote Huffman to Gizmodo in an email. “And to this day, none of them have detected Martian—or Earth—microbes or evidence of them. Which means that the COSPAR protocols are indeed working. So not only does their argument not hold together on its own merits, their claim that it is impossible to keep contaminants away from a planet like Mars has so far proven unfounded,” he said. To which he added: “My opinion is that if it ain’t broke, don’t fix it. The COSPAR protocols appear to be keeping Earth bugs off Mars while we study that planet for any native organisms. We shouldn’t mess with them, unless we wish to tighten them further.”




Huffman doesn’t disagree that eventually we might want to introduce microbes to Mars in the way the authors describe, but it would be “a huge scientific mistake to relax the COSPAR protocols on any world that we have yet to determine to be dead,” requiring us to keep “our bugs off Mars, Europa, Enceladus, and maybe even Titan,” he said. “At least for now.”

“We must follow the planetary protection equivalent of the Hippocratic Oath: ‘Above all else, do no harm.’”


Steve Clifford, senior scientist at the Planetary Science Institute, said he has “serious concerns” about the new paper. Ultimately, he believes the potential consequences of making a mistake by easing planetary protection standards “far outweigh any short-term gains.” We may eventually contaminate Mars, he said, but until then “we must follow the planetary protection equivalent of the Hippocratic Oath: ‘Above all else, do no harm.’”

“I believe that the potential contamination of an alien biosphere represents a serious ethical concern—because that is a legacy that we carry with us forever more,” Clifford told Gizmodo in an email. Like Huffman, he’s concerned that Earthly germs could complicate our ability to do science on Mars and said there’s no reason to believe current planetary protection schemes aren’t working.


“If life has evolved on Mars or the subsurface oceans of the icy moons of the outer planets, then it has likely survived on those bodies for billions of years,” said Clifford. “The detection of life on any of these bodies would have profound significance in our understanding of the prevalence of life throughout the universe.”

As for claims that implementing planetary protection protocols are too expensive, Clifford said the associated added costs, which typically amount to around 20 percent of the mission cost, are worth it.


“As we explore the potentially habitable environments in our solar system, we need to answer —as definitively as possible—whether any indigenous life is present, before we ever send humans there,” said Clifford. “And, if these environments prove lifeless, then the need for adhering to current planetary protection standards evaporates. However, should we discover life, then I believe that we must have a serious discussion that weighs our desire to colonize and utilize the resources of the solar system against the ethical concern of causing the potential extinction of the very first examples of alien life that we’ve found.”

At the same time, he doesn’t believe a kind of manifest destiny exists to colonize the solar system before we’ve had a chance to conduct a thorough search for alien life, “whether such a search takes 50 years or several centuries,” he said. Until then, “there are plenty of lifeless places in the Solar System—such as the Moon and asteroids—that humans can explore, colonize, and extract resources from,” said Clifford.


Lopez and his colleagues have obviously hit upon a sore spot. None of the experts we spoke to had major objections in terms of the use of microbes as part of the colonization and terraforming process at some future juncture. Rather, they were irked by the claim that we’re on the verge of transitioning from the exploration stage to the colonization stage and that we should start mobilizing our resources—and our microbial assets—accordingly.

As we approach an era in which we’re capable of sending humans to the Red Planet, this debate will undoubtedly continue to be a heated one.