The Caves That Could Help Us Find, or Become, Aliens | WIRED

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It’s a scene that sounds like it was lifted from Alien—a researcher interested in extraterrestrial life descends into the depths of a cave, where a droplet filled with creepy crawlies lands smack dab in her eye.

“I was like, ‘OK, I'm pretty sure that something alive fell in my eye,’” says Penelope Boston. She is now a portfolio scientist at NASA, but experienced this mortifying episode deep inside New Mexico’s Lechuguilla Cave in 1994.

Spelunkers often refer to their passion as catching the “cave bug.” In Boston’s case, the idiom was literal. Despite the injuries and harrowing moments she endured in her initial foray to the underworld—and the microbes that had to be carefully extracted from her peepers afterward—Boston came away “well and truly hooked.”

“After the pain and the pizza-sized bruises and all that healed, what I remembered was having seen this breathtaking environment with all of these spectacular mineral deposits, giant rooms, and bizarre sulfur deposits that looked like nothing I'd ever seen on the surface,” she says. “I always wanted to go to other planets. It didn't seem like we were going to do that anytime soon, but [caves] were my own private set of planets under our feet.”

In the decades since, Boston has pioneered the study of caves as ideal spaces to advance astrobiology, a field focused on the possibility of life in extraterrestrial environments. What began as a niche topic has since flourished into a thriving hub in the search for alien life as well as the possible expansion of humanity beyond the Earth, attracting attention from interdisciplinary researchers all around the world.

“The subject of life in a cave or life in an interstitial lake is the most probable way of expanding our knowledge of life in the universe, currently,” says Joshua Sebree, an associate professor of astrobiology at the University of Northern Iowa who specializes in cave environments. “There are lots of ideas across all the different government and nongovernment space agencies that are trying to figure this stuff out.”

Why Should We Look for Cave-Dwelling Aliens?

Caves on Earth are home to an astounding variety of habitats, from spectacular limestone karst caverns to dried basaltic lava tubes to marble hollows carved out by glacial retreat to underwater lairs and ice reservoirs.

They are often perfect shelters for animals such as bats, birds, crocodiles, or bears; indeed, our own human ancestors frequently used them as protective spaces from predators and weather, and eventually as hubs of rituals and social gatherings. But even in the darkest and deepest passages of caves, where sunlight can’t reach and the air might be toxic to humans, there are rich ecosystems of weird organisms eking out a living on chemical energy.

“What I was originally expecting was that these harsh environments, and that we’d see low biodiversity because you have to work hard to make a living," says Boston, who is the former director of NASA’s Astrobiology Institute. “But they were quite the reverse—extremely high biodiversity.”

The revelation that life can flourish even in sunless and otherworldly cave environments raises the question of whether alien life on Mars, or elsewhere, could find refuge in these subterranean structures, known broadly as “planetary caves.”

“There's this heavy component of understanding how air flow affects cave temperature that feeds in the potential for life,” says Jut Wynne, a cave scientist and ecologist at Northern Arizona University who has extensively studied extraterrestrial caves. “A shallow cave is presumably going to be less stable than a deeper cave. All of those factors will similarly impact or affect whether or not life could exist in a planetary cave.”

A benefit of caves is that they can provide protection from dangerous conditions on a planet’s surface, such as exposure to cosmic radiation or harsh temperatures. For example, it may be that caves deep under the Martian soil could be warmer, wetter, and more conducive to life.

“The queen of questions, from my point of view, is our prediction from 1992 that there could be a remnant microbial biosphere on Mars at depth,” says Boston.

What’s the Best Way to Search for Cave Aliens?

Over the past few decades, scientists have discovered hundreds of caves on the Moon and Mars, often by looking for “skylights” that expose cave entrances. In February, a team announced the discovery of a colossal lava tube under the surface of Venus that is several thousand feet in height and width.

Scientists have also speculated that ice caves filled with water, known as interstitial lakes, may be common in the frozen shells of moons like Europa, which orbits Jupiter, or Enceladus, which orbits Saturn. While these ice moons are famous for their subsurface oceans, the lake environments could provide potentially habitable pockets that may even receive