Sarah Stewart Johnson was a college sophomore when she first stood atop Hawaii’s Mauna Kea volcano. Its dried lava surface was so different from the eroded, tree-draped mountains of her home state of Kentucky. Johnson wandered away from the other young researchers she was with and toward a distant ridge of the 13,800-foot summit. Looking down, she turned over a rock with the toe of her boot. To her surprise, a tiny fern lived underneath it, having sprouted from ash and cinder cones. “It felt like it stood for all of us, huddled under that rock, existing against the odds,” Johnson says.
Her true epiphany, though, wasn’t about the hardiness of life on Earth or the hardships of being human: It was about aliens. Even if a landscape seemed strange and harsh from a human perspective, other kinds of life might find it quite comfortable. The thought opened up the cosmic real estate, and the variety of life, she imagined might be beyond Earth’s atmosphere. “It was on that trip that the idea of looking for life in the universe began to make sense to me,” Johnson says.
Later, Johnson became a professional at looking. As an astronomy postdoc at Harvard University in the late 2000s and early 2010s she investigated how astronomers might use genetic sequencing—detecting and identifying DNA and RNA—to find evidence of aliens. Johnson found the work exciting (the future alien genome project!), but it also made her wonder: What if extraterrestrial life didn’t have DNA or RNA or other nucleic acids? What if their cells got instructions in some other biochemical way?
As an outlet for heretical thoughts like this, Johnson started writing in a style too lyrical and philosophical for scientific journals. Her typed musings would later turn into the 2020 popular science book The Sirens of Mars. Inside its pages, she probed the idea that other planets were truly other, and so their inhabitants might be very different, at a fundamental and chemical level, from anything on this world. “Even places that seem familiar—like Mars, a place that we think we know intimately—can completely throw us for a loop,” she says. “What if that’s the case for life?”
If Johnson’s musings are correct, the current focus of the hunt for aliens—searching for life as we know it—might not work for finding biology in the beyond. “There’s this old maxim that if you lose your keys at night, the first place you look is under the lamppost,” says Johnson, who is now an associate professor at Georgetown University. If you want to find life, look first at the only way you know life can exist: in places kind of like Earth, with chemistry kind of like Earthlings’.
Much of astrobiology research involves searching for chemical “biosignatures”—molecules or combinations of molecules that could indicate the presence of life. But because scientists can’t reliably say that ET life should look, chemically, like Earth life, seeking those signatures could mean we miss beings that might be staring us in the face. “How do we move beyond that?” Johnson asks. “How do we contend with the truly alien?” Scientific methods, she thought, should be more open to varieties of life based on varied biochemistry: life as we don’t know it. Or, in a new term coined here, “LAWDKI.”
Now Johnson is getting a chance to figure out how, exactly, to contend with that unknown kind of life, as the principal investigator of a new NASA-funded initiative called the Laboratory for Agnostic Biosignatures (LAB). LAB’s research doesn’t count on ET having specific biochemistry at all, so it doesn’t look for specific biosignatures. LAB aims to find more fundamental markers of biology, such as evidence of complexity—intricately arranged molecules that are unlikely to assemble themselves without some kind of biological forcing—and disequilibrium, such as unexpected concentrations of molecules on other planets or moons. These are proxies for life as no one knows it.
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