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?
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