Less than a decade from now, a spacecraft from Mars may swing by Earth to drop off precious cargo: samples of the Red Planet’s rocks, soil and even air to be scoured for signs of alien life by a small army of researchers right here on our terra firma. Orchestrated by NASA and the European Space Agency, this fast-paced, multibillion-dollar enterprise, formally known as the Mars Sample Return (MSR) campaign, is the closest thing to a holy grail that planetary scientists have ever pursued.

In many respects, MSR is already well underway: NASA’s Perseverance rover is wheeling around an ancient river delta in Mars’s Jezero Crater, gathering choice specimens of potential astrobiological interest for future pick-up by a “fetch rover.” Then there’s the design and testing of the Mars Ascent Vehicle for lifting those retrieved samples into orbit for subsequent ferrying to Earth that is proceeding apace. But one crucial aspect of the project remains troublingly unresolved: How exactly should the returned samples be handled and at what cost, given the potential risk of somehow contaminating Earth’s biosphere with imported Martian bugs?

So-far-elusive answers to these questions could profoundly shape not only MSR but also the hoped-for follow-on of sending humans to Mars’s surface. Can astronauts live and work there without inadvertently introducing earthly microbes to the Red Planet? And perhaps more importantly, can they eventually return home with the certainty that they carry no microscopic Martian hitchhikers? The protocols hammered out for MSR will be a crucial component in resolving those eventual quandaries.

Risky Business

NASA’s present proposal for MSR calls for an as-yet-unbuilt interplanetary ferry to release a cone-shaped, sample-packed capsule—called the Earth Entry System—high above our planet’s atmosphere. The capsule will then endure a fiery plunge to Earth, sans parachute, ultimately landing in a dry lake bed within the Utah Test and Training Range. Despite impacting at roughly 150 kilometers per hour, the capsule will be designed to keep its samples intact and isolated. Once recovered, it will be placed in its own environmentally controlled protective container and then shipped to an off-site sample-receiving facility. Such a facility could resemble today’s biolabs that study highly infectious pathogens, incorporating multilayered decontamination measures, air-filtration systems, negative-pressure ventilation and myriad other safeguards.

Citing the findings of multiple expert panels, NASA presently deems the ecological and public-safety risks of this proposal as “extremely low.” But not everyone agrees. Earlier this year the space agency solicited public commentary on an associated draft environmental impact statement, netting 170 remarks, most of which were negative regarding a direct-to-Earth, express mail concept of Mars collectibles.

“Are you out of your minds? Not just no, but hell no,” suggested one commenter. “No nation should put the whole planet at risk,” another said. And another third opined, “Public opposition will surely rise drastically as the knowledge of [NASA’s] intentions are spread beyond the smaller space community.” Many of the respondents suggested that any shipment of specimens should somehow be first received and studied off-Earth—an approach that, while certainly prudent, could easily become a logistic and budgetary nightmare.

Contrast this with the blunt opinion of Steven Benner, a prominent astrobiologist and founder of the Foundation for Applied Molecular Evolution in Alachua, Fla.: “I do not see any need for long discussions about how samples from Mars should be stored once they reach our planet,” he says. That’s because space rocks striking Mars routinely eject material that ultimately ends up on Earth. Current estimates hold that about 500 kilograms of Martian rocks land on our planet every year, Benner says. He even has a five-gram hunk of Mars decorating his desk that alludes to that fact.

“In the over 3.5 billion years since life appeared on Earth, trillions of other rocks have made similar journeys,” Benner says. “If Mars microbiota exist and can wreak havoc on Earth’s biosphere, it has already happened, and a few more kilograms from NASA will not make any difference.”

Noting his service on many of the very same expert panels NASA now cites for its “extremely low” assessment of MSR’s risks, Benner says the space agency seems caught in a public relations trap of its own making, honor bound to endlessly debate the supposed complexities of what should really be considered simple, settled science. NASA now knows “how to look for life on Mars, where to look for life on Mars and why the likelihood of finding life on Mars is high,” he observes. “But NASA committees, seeking consensus and conformity over the fundamentals of chemistry, biology and planetary science that must drive the search for Martian life, displace the science in favor of discussions of these nonissues,” unnecessarily increasing the cost and delaying the launch of missions.

“They end up ensuring that NASA never flies any life-detection missions,” Benner says.

This illustration shows a concept for a proposed NASA Mars lander-and-rocket combination that would play a key role in returning to Earth samples of Mars material collected by the Perseverance rover. This Sample Retrieval Lander would carry a small rocket (about 10 feet, or 3 meters, tall) called the Mars Ascent Vehicle to the Martian surface. After using a robotic arm to load the rover’s sealed sample tubes into a container in the nose cone of the rocket, the lander would launch the Mars Ascent Vehicle into orbit around the Red Planet. The lander and rocket are part of the multimission Mars Sample Return program being planned by NASA and ESA (European Space Agency). The program would use multiple robotic vehicles to pick up and ferry sealed tubes containing Mars samples already collected by NASA's Perseverance rover, for transport to laboratories on Earth.
Credit: NASA/JPL-Caltech

Cautionary Costs

Such statements reflect a growing sense of urgency among U.S. planetary scientists about making MSR a reality. In April NASA received the latest Decadal Survey on planetary science and astrobiology, an influential report produced by the National Academies of Sciences, Engineering, and Medicine that las out near-future priorities for the field. One of the report’s main recommendations calls for the agency to shore up its plans for handling MSR’s samples, with an emphasis on readying a Mars Sample Receiving Facility in time to receive material from the Red Planet by 2031.

To meet that deadline, NASA must start designing—and building—such a facility immediately, says Philip Christensen, a professor at Arizona State University and co-chair of the new Decadal Survey’s steering committee.

“Our recommendation was to not go off and build a very fancy, very complicated, very instrument-rich receiving facility,” Christensen says. “Instead make it as simple as possible. The number-one job is to verify that the samples are safe, then let them go to labs around the world that already have very sophisticated instrumentation.”

John Rummel, a now retired astrobiologist who previously helmed NASA’s “planetary protection” efforts for its interplanetary missions, agrees that simplicity can save time but at uncertain costs. “Nobody wants to spend all the money in the world on a ‘Taj Mahal’ for [sample-return] science,” he says. Building a bare-bones facility could backfire, however, by failing to allow scientists to properly investigate whether any returned samples harbor evidence of life.

More fundamentally, Rummel says, it simply isn’t true that we know enough about Mars to quantify MSR’s risks of interplanetary contagion. “In the first place, we don’t know everything we want to know about Mars. That’s why we want the samples,” Rummel says. “We keep finding Earth organisms doing new things that are quite interesting from the standpoint of potential life elsewhere. So why don’t we think we need to be careful? The answer is that we do need to be careful, as repeatedly emphasized by the National [Academies].... People have to have some kind of respect for the unknown. If you have that respect, then you can do a credible job, and the public is well-served by your caution.”

All Together Now

Although MSR’s true risks for interplanetary ecological catastrophe may be unknown, the threat that negative public opinion poses for the mission is clear to most participating scientists. Even so, engagement with the public should be welcomed, says Penny Boston, an astrobiologist at NASA’s Ames Research Center. What better way to push forward the research needed to fill in knowledge gaps about planetary protection, she reasons, than getting people interested in the topic and its weighty stakes? “That will allow us to both optimally protect Earth’s biosphere and humans while still making the best full use of the analyses of the Mars samples to answer the science questions,” Boston says.

Similarly, while a chilling effect from harsh handling restrictions for MSR’s samples seems more probable than the eruption of some otherworldly pandemic from lax biosafety protocols, some argue that, in absolute budgetary terms, erring on the side of caution simply isn’t very expensive.

According to astrobiologist Cassie Conley, who succeeded Rummel as NASA’s planetary protection officer from 2006 to 2017, by the time MSR’s capsule impacts in a dry lake bed in Utah, “taxpayers will have invested at least $10 billion to bring these samples to Earth. So isn’t it worthwhile to spend 1 percent more to construct the best possible facilities and instrumentation for studying these samples while also ensuring that MSR doesn’t cause something bad to happen to the only planet we can live on?”

There is, however, one additional concern complicating the debate: MSR is no longer alone in its quest for fresh Red Planet rocks, and other projects may not abide by its still-emerging rules. China recently announced its own independent plans to bring Martian material directly to Earth, perhaps earlier than the NASA/ESA Mars Sample Return campaign, and there is also the “wild card” of Elon Musk’s Mars-focused SpaceX efforts leading to human voyages to Mars and back far sooner than most experts anticipate.

China’s entry in particular worries Barry DiGregorio, an astrobiologist and founding director of the International Committee Against Mars Sample Return (ICAMSR). “Unless [returning samples from Mars] is done as a global effort in order to share the findings in real time with all spacefaring nations instead of as a national goal, no single country will know what the other has found or what problems they are having with containment,” he says.

That’s why DiGregorio contends priority should be given to ruling out each and every sample’s prospects for harming Earth’s biosphere before it is brought back to our planet—something best done in a dedicated space station or even an astrobiology research lab built as part of a lunar base. “Of course,” he adds, given increasingly high global geopolitical tensions, “this concept will likely be a hard sell”—but now is the “critical time” to consider it.