When is it OK to kill an alien life-form?
In the movies, the answer is usually pretty simple: It’s OK in self-defense, especially if it inspires a rousing speech about human exceptionalism. But in the real world, the choice is neither straightforward nor abstract. Many missions to neighboring worlds could, accidentally or intentionally, disrupt extraterrestrial life. Under what conditions would the loss of a few aliens—admittedly, presumably microbes—be acceptable?
The range of views on this issue are diverse, fascinating, and essential to acknowledge as we pursue detections of life on other planets. Missions currently on Mars, as well as forthcoming missions to outer solar moons, including Jupiter’s moon Europa and Saturn’s moon Titan, could potentially encounter extraterrestrial forms of life. “It’s a question about what our priorities are, whether you are an astrobiologist or a member of the general public,” says Jayme Johnson-Schwartz, a philosopher who has written extensively about the ethics of space exploration.
NASA’s Viking mission, which landed the first robots on Mars in 1976, had a clear answer: Yes, it’s OK to kill a few aliens, as long as there is a scientific justification. The Viking landers carried out experiments on samples of Martian dirt; some were bathed in nutrients, and some were sterilized under searing temperatures. The logic was that any hypothetical microbes that got the spa treatment might perk up, producing detectable activity, while the microbes that were flamed would remain quiet, providing a control.
Let’s set aside the fact that the Viking experiment did seemingly detect signs of life, an outcome that remains controversial nearly 50 years later. (The general consensus is that the experiment found interesting chemical activity but that it can be explained without invoking life.) Just imagine if extraterrestrial beings came to Earth, rounded up some people, treated one group to a high-end meal and vaporized another just to make sure the first group was actually alive. It would be a strange introduction to a new species.
Of course the thought experiment falls short, because microbes are generally considered expendable on an individual level in a way that complex life-forms, like humans, are not, though it’s still an interesting reflection of our values about first contact. To that end, while we can’t avoid killing a few microbes here and there—either on Earth or potentially in space—whole ecosystems are another story.
The Committee on Space Research, an international nongovernmental organization dedicated to collaboration on space exploration, prohibits any activities that would pose a threat to an alien biosphere—or life on our own world, for that matter. This principle of “planetary protection” aims to avoid transfer of Earth life to other worlds (forward contamination) or alien life back to Earth (backward contamination).
“With the Viking mission, great care was taken not to introduce any terrestrial organisms that could potentially perturb any existing Martian biosphere,” said David Grinspoon, senior scientist for astrobiology strategy at NASA headquarters, in an emailed response that included input from Nick Benardini, NASA’s planetary protection officer.
“The Viking biological experiments did not risk harming any Martian ecosphere and were compliant with all [planetary protection] requirements,” Grinspoon adds. “The internationally accepted planetary protection protocols do not have any proscription against harming individual microbes when testing for the presence of life.”
In other words, the possibility of destroying a small population of aliens is an accepted risk of our exploration of other worlds. For instance, many space missions are equipped with a mass spectrometer, a precision instrument that vaporizes extraterrestrial samples in order to reveal detailed information about its constituent chemical parts—including, potentially, aliens.
Chelsea Haramia, an associate professor of philosophy at Spring Hill College in Alabama and a senior research fellow at the University of Bonn in Germany, says that the trade-offs of mass spectrometers and other instruments should be thoroughly hashed out in advance of missions.
“There is absolutely the risk that using such an instrument will endanger alien life, if it is present, and we hope that astrobiologists stop and think about the ethical considerations of employing this technique,” Haramia said in an email that included input from her colleagues Julia DeMarines, a graduate student in Earth and planetary science at UC Berkeley, and Emilie Lafleche, a PhD candidate in planetary sciences at Purdue University in Indiana, together with Michael Wong, an NHFP Sagan Postdoctoral Fellow studying astrobiology and planetary science at Carnegie Science in Washington, DC.
“To be clear, we’re not saying that mass spectrometry ought to be banned,” the group adds. “These instruments have provided exquisite data about the chemistry of faraway worlds, and they teach us plenty even when there is no life to detect.” But, they argue, astrobiologists should consider how their strategies might change if a mass spectrometer finds tantalizing evidence for extant life on another world. “Should we switch to less invasive techniques? Back off completely? Or just keep plowing away, given that the small sample size these instruments need is unlikely to disrupt an entire ecosystem?” We don’t yet have clear answers—but we should be pursuing them, the group says. “We ought to start asking ourselves these tough questions now, before we stumble upon the discovery of a lifetime.”
NASA’s Curiosity rover, which has been exploring Mars since 2012, has been able to determine that the planet was once habitable billions of years ago, among many other exciting discoveries, by zapping samples with its mass spectrometer. Mass spectrometers will be onboard NASA’s Europa Clipper mission, due for launch later this year, which will study gases from Jupiter’s moon Europa during several flybys, as well as being onboard the agency’s Dragonfly mission to Saturn’s moon Titan, which will land on the strange world sometime in the 2030s.
“The Dragonfly experiments will vaporize small amounts of ice from Titan in order to learn about the origin and evolution of Titan, help characterize its present day geological and meteorological processes, and assess the potential for organic evolution of the kind that may have led to the origin of life on Earth,” says NASA’s Grinspoon. “This mission is not designed to look for life, and it is extremely unlikely that these investigations would harm any hypothetical organisms.”
Grinspoon adds that NASA’s planetary protection office is involved in the design and approval of every mission launched to potentially habitable environments, and that spacecraft, including Mars rovers, go through a thorough sterilization process to avoid forward contamination of alien worlds with earthly microbes.
“There is always the slight possibility that simply through driving through a landscape or conducting experiments we could disturb an ecosystem,” he says. “In the case of the rovers, it is unlikely that living microorganisms exist at Mars’ surface, so the potential for disruption of an ecosystem is low.” Surface missions on Mars also avoid certain areas, known as “special regions,” because these areas possibly contain liquid water close to the surface, which raises the chance of there being life there to disturb.
In this way, astrobiologists and other specialists at federal space agencies, including NASA and the European Space Agency, weigh the potential impacts of their missions on any alien life-forms. But government entities are no longer the only players in space; the maturation of commercial spaceflight has revealed a new set of risks and attitudes about space exploration, including planetary protection concerns.
In 2018, for instance, the private spacecraft Beresheet crashed on Earth’s moon, potentially spilling its living cargo of hardy tardigrades, a type of very small animal, on the surface. (Equally, the tardigrades might well have been annihilated.) SpaceX CEO Elon Musk is also actively developing plans to establish human communities on Mars, so it’s worth considering what planetary protection guidelines should be in place for human missions visiting potentially habitable extraterrestrial environments, given that our bodies cannot be sterilized in a clean room.
Above all, it is critical to acknowledge the kaleidoscopic range of views that various communities hold about the value of life, both here on Earth or potentially elsewhere, so that these thorny issues can be confronted with input from as many perspectives as possible.
“It would take a lot of work to make Mars a place for us,” Johnson-Schwartz says. “If it’s already a place for something else, to me that is an important consideration against frivolously heading out to Mars to do whatever we feel like instead of coming together to think collectively about what we want for our first interaction with another world, and potentially other life-forms.”
“If we don’t come together and make sure voices are heard, and make sure that we find a way to impact policy,” she adds, “it’s going to be the wealthy that set the agenda.”
