Should Scientists Inject Saturn's Moon Enceladus with Life?

A new study proposes that seeding the orb’s underground ocean with microbes might help us learn how to make other worlds habitable

Enceladus (center) orbits Saturn in this 2007 image captured by NASA’s Cassini spacecraft. NASA / JPL / Space Science Institute

Injecting far-flung ice-covered lunar oceans with earthly microbes to see how life is shaped may seem like the diabolical plot of a comic book supervillain.

But researchers say that given the likelihood of liquid oceans lying under the surfaces of places like Enceladus, Titan or Europa—all moons of Saturn or Jupiter—now is a good time to take the idea of inoculating a world with life seriously.

“Could this be humanity’s first biosphere genesis experiment?” says Charles Cockell, an astrobiologist at the University of Edinburgh in Scotland.

Saturn’s moon Enceladus may be the best place to start with any questions about inoculating a foreign world with life, due to it having seemingly all the necessary ingredients for life as we know it, says Cockell and his colleagues in a study published this February in Space Policy. But even the idea of injecting life as a kind of experiment raises all kinds of questions, both ethical and practical. How can we be sure there isn’t life there already—and that we wouldn’t be disturbing the development of an alien ecosystem? What kinds of experiments would we want to run? What answers would they give us?

Most of what we know about the small Saturnian moon comes from NASA’s Cassini spacecraft. That craft studied the ringed planet from 2004 to 2017, flying around its many moons in the process.

Among Cassini’s major discoveries were plumes of water vapor and ice that regularly ejected out of Enceladus’ South Polar region. Scientists believe these eruptions are the source of the snow that covers the planet, making it the brightest object in our solar system. Subsequent flybys revealed that the material ejected from the moon contained elements like nitrogen, carbon, sulfur, hydrogen and phosphorous. “Those plumes have all the major elemental ingredients for life,” Cockell says.

Furthermore, these plumes were likely supplied by an underground liquid ocean, scientists believe. While the material ejected from those vents may not come directly from an ocean, the ocean still might be able to sustain life, Cockell says.

Dramatic plumes spray water ice and vapor near the South Pole of Saturn’s moon Enceladus. NASA / JPL-Caltech / Space Science Institute

But life may be there already, which presents the first major ethical conundrum in any discussion of inoculating other worlds with life from Earth. Ideally, to conduct an inoculation experiment, you’d want a world that is uninhabited but habitable. If already inhabited, then any introduction we might make could really throw the alien ecosystem out of whack.

Our own planet is already full of inoculation experiments gone wrong. Mongoose were introduced to Caribbean islands in an effort to control the rat problem, but they quickly ran wild, causing all sorts of problems for the native ecosystems in places like Jamaica and Trinidad, for example. Poisonous cane toads were imported to Australia, Hawaii and other areas from mainland Central and South America to try to control crop pests and ended up doing massive damage to native predators. Researchers would have a difficult time predicting the kind of destructive effect that introducing foreign microbes into a potentially fragile alien ecosystem may have—even if they had the tools to definitively detect life on Enceladus.

“We have very sensitive instruments, but I don’t think they are significantly sensitive now to make the declaration that a world is not inhabited,” says Morgan Cable, a planetary scientist at NASA’s Jet Propulsion Laboratory at the California Institute of Technology who was not involved in Cockell’s recent paper. She says she wouldn’t be satisfied herself that no life existed without exploring every crevice. While Enceladus is small—about the size of Arizona—this would still be incredibly difficult, she says.

And some rules, or at least guidelines, exist about contaminating potential alien ecosystems. The Committee on Space Research, an international consortium that aims to advance space science, has specific ethics about the exploration of Enceladus and Europa—the latter a moon of Jupiter that also may have an underground ocean. These guidelines state that there has to be an infinitesimally small chance of contamination by any space craft or its parts within 1,000 years of contact. “Requirements for Europa and Enceladus flybys, orbiters and landers, including bioburden reduction, shall be applied in order to reduce the probability of inadvertent contamination of Europan or Enceladan subsurface liquid water to less than 1x10^-4 per mission”—a fraction of a chance—the guidelines state.

This means that any lander to set down, even briefly, on one of these moons would have to be completely sterile. Or, since that may be impossible, any possible vagrant microbes that survived would have to have little chance of contacting the underground ocean within a millennium.

“We’re giving ourselves a time buffer so we can fix potential problems,” says Cable. In other words, if researchers contaminated the surface of Enceladus, they would have a millennium to determine a way to stop the contaminant from spreading to the underground ocean.

In 2008, NASA’s Cassini spacecraft came within about 16 miles of the surface of Enceladus and captured images used to make this mosaic. NASA / JPL / Space Science Institute

Both Cable and Cockell are uncomfortable with the idea of humans “playing God” by putting life on a new world—especially if there is a chance that some form of life already exists there.

But Cable thinks now is a good time to begin the discussion of potential inoculation. “I like what he’s doing in this paper, which is opening up the floor for discourse,” she says.

If researchers could be reasonably sure no life exists on Enceladus, more questions arise on what steps they might take to inoculate the moon. Cockell says that it would be incredibly important to perform the experiment properly the first time, because once life takes hold, it would be impossible to start the experiment again, unless multiple, unconnected underground oceans occur on the moon, which could offer scientists the opportunity to run multiple parallel experiments.

One pathway for inoculating the moon would be to first introduce methanogens, a simple microbe that can convert hydrogen and carbon dioxide and produce biomass. “In theory, once you’ve done that, you’ve got the basis of a food chain,” Cockell says. Then, you might wait and see what happens, or introduce other microbes that could eat living or dead methanogens, and get increasingly complex from there. “What you could see is a sort of experiment that would run over centuries, millennia,” he explains.

On other worlds with oceans, scientists could run other types of experiments to compare the results with those of Enceladus.

Scientists could inoculate Enceladus using a probe—something that would melt through the icy crust to get to the liquid before opening. Several grams worth of material would be enough to begin the experiment, Cockell speculates, though researchers would need to understand more about how the ocean mixes to predict how long it might take these microbes to colonize the moon. Spacecraft could fly through the plumes collecting sample material every decade or so to see how the biological experiment progresses.

Other possible technology, both for sampling and for inoculating, is already in development, Cable says. The Exobiology Extant Life Surveyor project is building a snake-like device that could travel down the vents of Enceladus to reach the underground ocean—assuming the vents are connected to the water. Different segments in this device could collect and analyze samples, transmitting the information back to Earth without having to return with the actual material. This could tell researchers if the microbes have taken hold, if they have evolved and how quickly.

Exobiology Extant Life Surveyor (EELS) Concept of Operations on Enceladus

Observing how life evolves on Enceladus might teach us how life evolved on our own planet, or how life persisted during Snowball Earth—cold times in our past when our planet was entirely covered by ice. In other words, the best way to see how life may have formed in the first place on our planet may be by seeing it happen firsthand on another world.

But experiments in inoculation could also help to inform any future efforts of colonizing other planets, whether that means our own moon, Mars or a world further afield. Even if we aren’t going to live in a place that is relatively inhospitable like Enceladus’ underground ocean, the results could still be very informative for the seeding and fostering of life off Earth.

“If we are going to live on other planets, we are going to have to figure out how to build biospheres,” Cockell says.

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