Last week at the 67th International Astronautical Congress (IAC) in Guadalajara, Mexico, the billionaire entrepreneur and SpaceX CEO Elon Musk detailed his dream of “ensuring the light of consciousness is not extinguished,” an audacious plan to make humanity a multi-planetary civilization and insulate it from extinction by building gigantic rocket ships to ferry one million homesteaders to Mars—and beyond. After his hour-long talk Musk asked for questions, undoubtedly hoping for a stimulating and thoughtful discussion.

What followed was a sequence of interrogative non-sequiturs, as one eager audience member after another bombarded him with bizarre requests. Musk’s presence at the normally august proceedings of the IAC had brought his diehard fans out in force, and for a time the sanest person in the room seemed to be the man on stage pitching plans to land a million people on Mars. One questioner asked to toss Elon a comic book; another tried to lure him into a prototype 30-ton electric bus in the parking lot; a producer affiliated with the website Funny or Die sought to sell him on a video series starring Michael Cera as the first astronaut on Mars, and someone named “Lara” offered to “go upstairs” with him for “a good-luck kiss.” Only a few professional journalists managed to squeeze in questions around this cavalcade of characters, chiefly asking about the technical and financial feasibility of Musk’s ambitious plans.

The most important question, though, inadvertently came from someone called “Aldo” who opened with a boast about his recent consciousness-expanding attendance of Burning Man—an annual arts and music festival in the Nevada desert. Was the lack of liquid water on Mars, Aldo wondered, going to make Musk’s hopeful colony “a dusty, waterless shitstorm” just like Burning Man? How would SpaceX develop “sustainable sanitation” for colonists on such a frigid and desiccated world? Wouldn’t human waste be a big problem there? Musk matter-of-factly replied that since water ice was plentiful on Mars, the real trouble would be producing enough energy to melt it all, rather than making do with waterless toilets.

Musk’s answer—like Aldo’s question and all the others asked in Guadalajara that day—cavalierly overlooked the most vexing quandary facing human voyages to Mars: If there is life there—even just alien microbes clinging to existence in the Red Planet’s isolated refuges—any biological contamination we import from Earth could cause an ecological and scientific catastrophe. We may well be our solar system’s sole spark of sentience and technology, but we are also undoubtedly messy, microbe-riddled animals carrying about a kilogram’s worth of bacteria in our guts, lungs and skin. Without careful (and as yet largely undeveloped and untested) countermeasures, something as simple as a leaky spacesuit, greenhouse dome or sewage main could unleash the hardiest members of our microbiomes to spread and colonize much of Mars before we do. Such an outbreak of invasive microbes could easily wipe out any fragile indigenous biosphere, and with it our hopes for finding and studying an example of truly alien life. Should our civilization’s insatiable curiosity and hunger for frontiers override the welfare of alien creatures, even if only microbes? Would sending humans to Mars be worth the price of planetary-scale ecocide? (I have covered this topic more thoroughly elsewhere, particularly in my recent feature on the scientific debate over where to land the first humans on Mars.)

This is, of course, not a new problem—space agencies have been researching “planetary protection” for decades for missions to Mars and other interplanetary destinations, and NASA even has a full-time position for a Planetary Protection Officer, currently held by the biologist Catharine Conley, to enforce planetary protection protocols. Those protocols are codified by an international organization called the Committee on Space Research, and stem from the United Nations Outer Space Treaty of 1967, which forbids the “harmful contamination” of other planets. But current rules only cover lifeless machines, which can be baked in ovens, washed with antimicrobial chemicals and blasted with bacteria-killing radiation.

The strictest sterilizations are reserved for spacecraft visiting so-called “Special Regions” on Mars, places where satellite observations suggest liquid water and other hallmarks of habitability could still persist. A rover or lander going to a Special Region would have a total budget of 300,000 bacterial hitchhikers, less than the number in a single square-millimeter colony dotting a petri dish—an amount that naïve back-of-the-envelope calculations suggest yields a one-in-10,000 chance of Earth’s bacteria gaining a flagella-hold upon Mars. Naturally, Special Regions would also be prime locales for any future settlers arriving on SpaceX’s super-rockets. But landing a single human in such places—let alone a million of them—would totally break the reigning planetary-protection paradigm.

As of yet, there are no feasible solutions to this problem other than to simply not go, or to instead flout or rewrite the rules. (Incidentally, there seems to be no clear penalty or enforcement mechanism for non-state/corporate rule-flouters, either.) Musk, for his part, seems to see planetary protection as a non-issue, remarking in 2015 that he believes Mars’s surface to be utterly sterile, with any indigenous microbes relegated to the inaccessible depths of the planet’s subsurface.

Contrary to Musk, the staunchest proponents of planetary protection recommend that rather than rush headlong to land humans on Mars, we should first focus on sending them to its small moons Phobos and Deimos. “If we keep our filthy meatbag bodies in space and teleoperate sterile robots on the surface, we’ll avoid irreversible contamination of Mars—and obfuscation of the answer to the question of whether we’re alone in the solar system—for a little while longer,” writes Emily Lakdawalla, an influential blogger for The Planetary Society. “Maybe just long enough for robots to taste Martian water or discover Martian life.”

Not all scientists hold such restrictive views. Many argue that, Special Regions aside, Mars is simply too inhospitable to allow the widespread flourishing of invasive microbes from Earth, even though laboratory tests have shown some bacteria commonly associated with humans can thrive in Martian conditions. Some instead believe that planetary protection is futile, because Earth’s biosphere should have already thoroughly contaminated Mars via earlier spacecraft and ancient fragments of rock sent on interplanetary voyages by enormous asteroid impacts. Others, such as Steve Squyres, a Cornell University planetary scientist who heads NASA’s Mars Exploration Rover Mission, prefer to pragmatically note that even if life does exist on Mars, we may never find it if we don’t go there in the flesh. “What Spirit and Opportunity typically achieve in a day,” Squyres told Congress in 2009, “a human explorer could do in less than a minute.”

All these arguments have remained largely academic for decades, as NASA and other space agencies have periodically considered—and subsequently abandoned—sending humans to Mars. Now NASA officially plans to send astronauts to Mars sometime in the 2030s and is building its own giant rocket and crew capsule, the Space Launch System (SLS) and the Orion Crew Exploration Vehicle, to this end. Many experts believe political interference will delay or defer NASA’s ambitions because of the colossal expenditures associated with SLS and Orion, which are forecast to have consumed about $30 billion by the time they carry their first crew of astronauts on an early-2020s flight that is slated to simply circle the Moon.

Musk, by contrast, claims SpaceX can develop the key rocketry required for his vision for as little as $10 billion and can send the first people to Mars in the mid-2020s—offering little breathing room for scientists, engineers and policymakers hoping to solve the problem of planetary protection before then. If Musk’s predictions prove remotely accurate, we could be seeing the emergence of a hard deadline for scientists hoping to continue remotely exploring a relatively uncontaminated and untrammeled Red Planet. Should the scientific community bet for or against Musk and SpaceX? I don’t know. But it’s clear that if and when humans land on Mars, all bets will be off.