How to spot an alien

In the last three decades, astronomers have identified over 6,000 confirmed exoplanets. Even chemistry we’re familiar with on Earth could play out in surprising ways in extraterrestrial environs, giving rise to life-forms that wouldn’t resemble anything we’ve seen before. (When you consider the fact that yellow dwarf stars like our sun constitute just 6% of the universe’s stellar population, our system starts to seem like the weird one.) We have to consider the dazzling number of other planets and moons in faraway systems different-looking from ours that might also be inhabited. We have to be open to being surprised. In Proxima Kósmos, we engineer the conditions to let surprise bloom.

Over the last three years, I’ve brought together planetary scientists, astrobiologists, speculative designers, and science fiction writers to model hypothetical forms of alien life through both science and storytelling. Employing what I call a methodology of scientific surprise, world-class scientists have been playing with the levers of life to dream up biologies never before conceived. And sci-fi writers have been telling stories of these worlds as human or alien life might encounter them.

The life-forms are speculative yet plausible. Given what we know of biochemistry, these physical manifestations of life and their environments really could exist in the universe—in the past, now, or in the future. Proxima Kósmos is meant to cultivate our imagination so that when life does turn up, we are ready to encounter it and recognize it as such.

Phaínōterra, shining Earth

For the host star of the Proxima Kósmos solar system, I chose an orange dwarf—dimmer and cooler than our sun. Orbiting it are nine planets, including worlds such as Magikos, where technology and biology have matured together; Ákroterra, or “Extreme Earth,” where microbial and fungal networks display extraordinary collective intelligence in unlikely, harsh conditions; and Phaínōterra, which resembles Earth’s neighbor Venus.

The ideas behind Phaínōterra—from the Greek words phainein (to reveal) and phōs (light)—came about through a collaboration with Sara Seager, professor of physics, planetary science, and aero-astro, and MIT postdoctoral student Iaro Iakubivskyi. Together, we designed this “Phosphine Earth” to illuminate what sulfuric acid environments on Venus-like exoplanets might be like. (When I visited Seager’s lab, she showed me how just a few hostile drops of acid had gobbled up her lab coat!)

Researchers imagine that Phaínōterra (left) harbors microbial life forms with collective intelligence like that of ant colonies on Earth. And on the fictional Nousterra (right), light is life and intelligence is ambient.

Xenoterra (left) is envisioned as home to complex virtual creatures and Ákroterra (right), as a cold, high-radiation planet that harbors resilient cave-dwelling organisms.

For decades, the astrobiology community has dismissed the idea that Venus might engender the conditions for life. Yet in 2020, a team of scientists including Seager detected phosphine (PH₃)—a potential biosignature gas that could indicate biological activity—at parts-per-billion levels in Venus’s atmosphere. They followed this anomaly, postulating that the upper atmosphere might contain neutralized salt particles that would create localized regions of lower acidity—and perhaps allow for some biological flexibility.

To showcase how life might inhabit sulfuric acid cloud environments on a Venus-like world, Seager and Iakubivskyi envisioned mountains whose peaks grazed the planet’s higher, cooler altitudes. There, sulfuric acid droplets might condense into pools, as water does on a glass holding an icy drink on a hot summer’s day. “We’re imagining the clouds to be yellowish, like they are on Venus,” Seager says. “We’re imagining that if we could get a glimpse below the clouds, we’d see pools. Not giant lakes, but little mountain pools of liquid sulfuric acid. For fun, we’re imagining the pools also contain small amounts of other ingredients, making them bright blue.”

Exploring whether anything might be able to survive—and perhaps even thrive—in these hypothetical pools involved a field trip, a cloud chamber, and lab experiments that yielded surprising results.

Building an alien world

To study Venus on Earth, we sent Iakubivskyi to Lake Ijen, nestled in the mountains on the island of Java in Indonesia. Lake Ijen’s seductive, incandescent turquoise color belies its hostility to earthly life; its 0.3 pH makes it the most acidic crater lake in the world. Just as the Mars Desert Research station in Utah helps scientists role-play working on another planet (astronaut suits and all), Lake Ijen served as a Venus analogue that Seager and Iakubivskyi used to characterize the fictional planet Phaínōterra. “It’s a way to anticipate alien biologies beyond Earth,” Iakubivskyi told me.

When Iakubivskyi arrived at Lake Ijen, he was met with thick clouds of acidic volcanic gas, treacherous terrain, and even a mini earthquake. He carefully steered a drone over the lake, using a system custom-designed for acidic lakes to capture samples. Armed with insights from Lake Ijen, Iakubivskyi returned to MIT, where he built an enclosed, boxy particle detector called a cloud chamber in Seager’s lab in Building E25 and injected concentrated sulfuric acid to simulate the clouds of Venus. 

Meanwhile, Seager’s lab and collaborators conducted experiments exploring whether biological building blocks could survive in highly acidic environments like those of Venus and Venus-like exoplanets. One involved mixing “biogenic” amino acids—those essential to all life on Earth—with sulfuric acid at concentrations known to exist in the clouds of Venus. Out of 20 amino acids they tested, 19 survived. Even more surprising, all 19 were stable for at least a month, with a handful chemically modified by the acid, and the team found that some small peptides, nucleic acid bases, and lipids also persist in sulfuric acid. This research showed that biological building blocks could remain stable in what was thought to be an environment completely inhospitable to life.

How could life eke out an existence in places long thought to be totally uninhabitable?

Separately, while readying sulfuric acid mixtures for mass spectrometry analysis in preparation for future Venus missions, Seager’s lab discovered that sulfuric acid mixed with an organic compound didn’t completely evaporate, even in a vacuum. In further experiments with collaborators, mixing sulfuric acid with various nitrogen-bearing organics (such as those that could be delivered to Venus and Venus-like exoplanets by meteorites) produced ionic liquid, a fluid mixture of salts that stuck around. The work revealed that sulfuric acid environments can produce a new kind of liquid that might itself sustain life. 

“Our specific biological path only works with what we have on Earth,” Iakubivskyi says. “But if you swap the parts from the beginning, life could potentially exist in these solvents.” And that chemistry in an alien environment could perhaps nurture life just one planet away from Earth.

Seager’s lab is now using insights from both the Phaínōterra cloud chamber and the sulfuric acid chemistry experiments to design instruments for a Venus habitability probe mission targeted to launch in the 2030s.

Not-so-basic chemistry?

When scientists led by the Nobel Prize–winning microbiologist Joshua Lederberg pioneered space biology in the 1950s, they entertained all kinds of chemical combinations that might have produced life in our backyard. As they anticipated NASA’s upcoming missions to the moon, Mars, and even Venus, they imagined that organic compounds might litter the extraterrestrial environment and hypothesized that the same ingredients could have brewed wholly alien molecules, cells—and even creatures.

Later, in the 1970s, the astronomer, planetary scientist, and author Carl Sagan envisioned a rock-eating creature on Mars—which would crunch through stone to get to water—and even an ice-fed plant. “I could imagine a kind of plant—a plant is perhaps how one would identify it—that is indeed an ice-eater with fine root-like structures,” Sagan mused in the animated NASA film Mars: The Search Begins, “searching not for liquid water, but searching the permafrost, reaching down to get at ice.” For Sagan and other exobiologists, such possibilities were “imaginative idea[s], but not wholly ridiculous.” In the early days of space biology, creative fabulation helped drive scientific imagination—a perspective at odds with today’s more conservative approaches.

The space missions in the late 1960s and ’70s that focused on life beyond Earth, however, came up short. Sagan had seen what he posited might be huge tangles of vines on the cliffs of Mars, but space photographs by Mariner 9 in 1972 identified them as merely geological features. When the Viking missions launched in 1975 failed to turn up any conclusive traces of extinct or extant life on Mars, space biology entered a period of hibernation. Yet as astronomers started to detect more and more exoplanets in the 1990s, the possibility space for extraterrestrial life exploded. Basic chemical research simulating alien environments has not yet caught up.

Thinking like an alien

Asking questions is an imaginative act that can drive scientific experiments. What would Earth be like if it orbited a red star? How would extraterrestrial beings transmit a message to Earthlings so that we might read it? How could life eke out an existence in places long thought to be totally uninhabitable? Such questions can help researchers make the alien more familiar and use Earth-based frameworks of life as a launching point for their work. Simultaneously, they can help scientists imagine Earth biologies as alien ones, allowing them to approach life’s possibilities with fresh eyes.

Sagan’s and Seager’s acts of imagination are playful. Rock-eating Martians might now seem fanciful. The planned Morning Star missions designed to study Venus’s habitability may very well turn up squat. But the mode of storytelling that these scientists engage with opens up space to be truly experimental.

The Proxima Kósmos project simulates life as it could be by building open-ended experiments using chemistry and computer modeling. We hope to stitch the hypothetical to the discoverable and contribute to a confirmed detection of extraterrestrial life. Despite that life’s elusiveness, the act of seeking has reformed how we humans define life itself and our place in the cosmos. 

Claire Isabel Webb, PhD ’20, is director of the Future Humans program at the Berggruen Institute, a nonprofit based in Los Angeles. Proxima Kósmos, her keystone project, is best explored on desktop at www.proxima-kosmos.com. It was inspired by her time as an MIT grad student working with David Kaiser, professor of physics and the history of science, to tell stories about the history of the search for life beyond Earth since the 1950s.