What could alien life look like? These Earthlings offer clues.

For generations, science fiction has imagined what life might look like on other worlds.

Novelist H.G. Wells described nightmarish squid-like Martian invaders in The War of the Worlds, while the Superman franchise envisioned enhanced humanoid aliens. Today’s blockbusters have put forth everything from the hand-like “heptapods” of Arrival, to a territorial saucer in Nope, to the crablike extraterrestrials that must join forces with humans in Project Hail Mary. 

These aliens are fictional, sure, but some of them are informed by real evolutionary processes on Earth. That’s why, despite the immensity of space, some scientists argue the best place to begin the search for aliens might be right here at home—on the only planet we know for certain hosts life. 

Scientists from a variety of backgrounds are refining the search for extraterrestrials through the lens of Earth’s most intriguing terrestrials, from miniature microbes to massive marine mammals. They argue that our fellow Earthlings can help us understand how life could potentially emerge and survive in the galaxy’s most extreme environments. These animals may even offer hints as to how we might communicate with intelligent alien civilizations.

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Perhaps most importantly, turning our lens to our fellow Earthlings may open our minds to the possibility that aliens may not look or sound or behave like anything even the most creative science fiction writers have ever dreamed.

“With science fiction, you tend to have this big bias towards humanoid lifeforms that are more or less exactly like us, or pretty close to what we're like,” says André Antunes, a microbiologist and dean of the Institute of Science and Environment of the University of Saint Joseph in Macao, China. "Peoples’ imaginations have been populated with this scenario of little green men for such a long time.”

But aliens may have evolved wildly different anatomies, more akin to extremophile microbes or perhaps the heptapods of Ted Chiang’s novella “Story of Your Life,” which inspired Arrival. And they might speak to us to ways that sound nothing like human language. “I think it's cool when you think a little bit outside of the box,” Antunes says.

Life forms that even fiction has yet to imagine

Earth may be the only habitable planet we know of, but it still has plenty of seemingly uninhabitable patches. Miles under the ocean, beyond the reach of sunlight, hydrothermal vents leak boiling water out of the seafloor. Freezing cold lakes hide deep under polar ice sheets. And there are also extraordinarily salty environments like Great Salt Lake or the Dead Sea. There is even the open sky of the stratosphere, dozens of miles above a planet’s surface.

Amazingly, microbial life can be found thriving in all of these unlikely places. To that end, much of the search for extraterrestrial life is shaped by the principle that simpler organisms are likely more common in the cosmos than they are in science fiction. 

Indeed, many scientists suspect that microbial life may even exist somewhere in our own solar system. This prospect raises the question of how we might be able to spot it.

Here on Earth, researchers are gaming out what form this life could take by recreating alien environments in the lab. Alexandre Rosado, a professor of bioscience at King Abdullah University of Science and Technology, studies extremophiles that thrive in harsh conditions similar to those on Mars or icy ocean worlds that are thought to have potential to harbor microbial ecosystems. By simulating these conditions, scientists can better understand how microbial life might survive elsewhere and what detectable signatures it could leave behind.

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“If we were to find even a simple microbe beyond Earth, for example, in a Martian brine or beneath the icy crust of Europa, it would answer one of the most fundamental questions in science: Is life a rare accident, or a natural outcome of planetary chemistry?” Rosado writes in an email.

Rosado says these simulated experiments provide a roadmap for identifying what metabolisms and survival strategies are viable in harsh environments. For example, when microbes endure extreme stress in experiments, they often slow down their activity or enter dormant states.

“That means life on another planet might not look like an active ecosystem, but instead leave subtle biosignatures such as trace gases, unusual mineral signatures, or molecular fragments,” Rosado explains. “By studying extremophiles under these simulated planetary conditions, we gain a much sharper sense of the clues future missions should look for and how to interpret them. In that way, our experiments help move astrobiology from speculation toward a science grounded in real, testable expectations of what life beyond Earth might actually look like.”

Microbes that thrive in high-salt environments, known as halophiles, offer another compelling model for extraterrestrial life. Antunes says halophiles can survive in tiny water pockets inside salt crystals—enduring extreme dryness, radiation, and chemical stress—for tens of thousands of years. Scientists have discovered fossilized microbes in salt crystals from Australia that date back nearly a billion years. 

As such, he argues, it may be that there are extinct microbes waiting to be found within Martian salt crystals or in the likely salty subsurface oceans of icy moons in the outer solar system such as Jupiter’s moon Europa or Saturn’s moon Enceladus.

This research also extends beyond our solar system. Lisa Kaltenegger, a professor of astronomy and founding director of the Carl Sagan Institute at Cornell University, has spent much of her career thinking about how alien life might leave detectable traces on distant worlds, particularly in the atmospheres of exoplanets. In her 2024 book Alien Earths: Planet-Hunting in the Cosmos, she explores the idea that alien organisms could produce visible signs, like the glow of biofluorescent life or colors in the sky caused by pigments produced by microbes.

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Her team collects samples of life from extreme environments on our own planet, including atmospheric microbes that drift miles above Earth’s surface. “We're trying to get samples from everywhere—from the desert, from the hot sulfur springs, everything,” she says.

The reason for gathering these Earthly examples is simple: The diversity of life here expands the aperture for possible biosignatures elsewhere. “We have 250 different kinds of life with different colors, and it's freely available online for anybody to use,” she says. “The key point is, I don't want us to miss signs of life looking for the wrong thing. Don’t just look for green!”

The animals that may help us communicate with aliens

If we ever spot an alien civilization, the next task is to learn to communicate with them. One way to prepare for that moment, scientists say, is to listen into the conversations that might be happening all around us.

Arik Kershenbaum, a zoologist at University of Cambridge, has done so extensively as part of his research into xenolinguistics—the study of extraterrestrial languages. In his 2020 book The Zoologist’s Guide to the Galaxy: What Animals on Earth Reveal About Aliens—and Ourselves, he argues that the principles of natural selection are universal across the cosmos. Consequently, aliens will face similar evolutionary pressures to Earthlings, and may develop analogous adaptations, such as social organization and complex communication.

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“I think that many of the animal behaviors we see on Earth are fundamentally universal, such as living in groups,” Kershenbaum says. That doesn’t necessarily mean that social behavior would look the same among aliens as it does among us—after all, he says, “sociality existed on Earth at least 600 million years before humans existed.”

In other words, it’s possible that alien expression may more closely resemble the mimicry of parrots or the whistles of dolphins than human language. By eavesdropping on animal vocalizations, we can open our minds to those forms of communication.

Take sperm whales, an animal that last shared a common ancestors with humans some 90 million years ago. These mammals “allow us to test a more complex and alien form of communication than working with a close primate relative,” says David Gruber, a National Geographic Explorer,  and the founder and president of Project CETI (Cetacean Translation Initiative). (The organization’s acronym was inspired by the term used for the search for extraterrestrial intelligence, SETI.)

This interdisciplinary collaboration is focused on deciphering sperm whale communication, with an eye toward laying the groundwork for any future contact with aliens.

“We are developing the tools that could be cross-applied to translate any non-human system, including an alien, if and when there is ever a discovery of an intelligent life form on another planet or galaxy,” says Gruber.

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Gruber believes that sperm whales offer a powerful model for alien communication. The iconic marine mammals have developed tightknit matriarchal societies that communicate through intricate patterns of clicks and so-called “codas,” which they use to pass down critical knowledge across generations. 

Gruber and his colleagues have made a number of discoveries about the components of sperm whale speech, with the aim of eventually translating the possible meanings of these enigmatic expressions. So far they’ve discovered that sperm whale clicks contain sonic qualities similar to human vowels, that they use vocalizations to coordinate behavior, and that they provide cooperative assistance to birthing females, similar to midwives, a practice that had never previously been observed in any non-primate species.

Successfully communicating with aliens will require plotting out all the intricate steps involved in translation—something few people consider when they imagine a “first contact” scenario, says Gruber, who is also a distinguished professor of biology and environmental sciences at the City University of New York, Baruch College, and the CUNY Graduate Center. Sperm whales are an ideal “testbed” for this step-by-step computerized decoding process. The same concept has already shown up in science fiction works, including in Project Hail Mary, which involves alien-human translation software.

A scientifically curious species

Several experts argue that any first contact moment is likely to involve another scientificially curious species. Kershenbaum likens it to the sci-fi classic Contact, a 1985 novel written by Carl Sagan and adapted into a 1997 film about the discovery of a message from an extraterrestrial civilization.

“If you read this really wonderful novel, whoever sent this message knew that scientists would interpret it, and therefore they would try to find that logical pattern,” Kershenbaum says. “I think that's really the key.” 

Regardless of what form extraterrestrial life might take, its discovery would fundamentally alter our understanding of the universe, and our place within it. Plus, no doubt it would inspire even more great sci-fi.

“I love the diversity of sci-fi right now because we are finding more and more of these really interesting planets that are different than ours,” says Kaltenegger. “If we would have found only carbon copies of the Earth, the sci-fi realm would be much poorer.”