for billions of years, our planet was nothing like Earth. It was Earth, of course. But if you looked at it from space, it kind of resembled a giant orange jawbreaker.
Most people don’t realize that Earth’s atmosphere wasn’t always the one we have right now. Its first atmosphere presumably had a lot of hydrogen gas, which was very quickly (relative to the planet’s 4.5-billion-year history) stripped away by solar wind. Earth regenerated a new atmosphere of primarily carbon dioxide, and maybe some water vapor and nitrogen, but no oxygen.
Yet there was life on the planet—anaerobic organisms to which oxygen was poisonous. Eventually, though, the cyanobacteria present in huge numbers on Earth’s surface began to produce oxygen as a byproduct of photosynthesis, and it built up in the atmosphere, causing a mass extinction. Life shifted into a different phase. Fueled by that oxygen, it evolved, became more complex. Advanced life on Earth, the air that we breathe, we owe to cyanobacteria from more than 2.5 billion years ago.
Jacob Bean, an astronomer and astrophysicist at the University of Chicago, is explaining all this to me in his fifth-floor office in the William Eckhardt Research Center, a gleaming glass building at 56th and Ellis. He speaks with a round and genial Southern accent that sounds like Matt Damon playing a farmer. Standing 5-foot-9, Bean, 43, has a strong jaw, a shaved head, and the posture of a cactus. Wearing a cream-colored sweater, dark jeans, and lime-aqua Hoka sneakers, he looks like a personal trainer, not someone who cocreated a pioneering astronomical instrument called MAROON-X, a much-flashier name than what it stands for: “M dwarf Advanced Radial velocity Observer Of Neighboring eXoplanets.”
For now, ignore what any of that means except for the last word. “Exoplanet” is short for “extrasolar planet,” denoting any planet outside our solar system — that is, not orbiting our sun. Astronomers estimate there are 100 billion stars in our galaxy alone, nearly all orbited by at least one planet, and 100 billion galaxies in the known universe. That’s a lot of planets! And endless avenues of inquiry for Bean, whose specialty is exoplanets. “It’s called job security,” Bean says.
For a long time, exoplanet science was a fringe sector of astrophysics. When Bean was a graduate student in the mid-2000s, virtually no one wanted to concentrate in it. Since then, however, aspiring astrophysicists have come to realize that exoplanets are the key to understanding not just the nature of planets but the evolution of Earth’s atmosphere, helping us fill in the gaps of our knowledge about our planet’s past and even its future. Today, Bean surmises that exoplanet specialists make up roughly 25 percent of the field. And within that community, he’s on the forefront. “He’s one of the world leaders in the field, without question,” says Sara Seager, an astrophysicist at the Massachusetts Institute of Technology.
In addition to running the university’s Bean Exoplanet Group, a nine-person research team, Bean coleads the Early Science Release Program on the James Webb Space Telescope, the trailblazing, paradigmshifting instrument that launched in late 2021. That means he’s one of some 300 scientists who get the first look at data generated by the telescope, which he analyzes for atmospheric characterization of exoplanets.
It’s a good position to be in, because the telescope promises to revolutionize our understanding of these mysterious worlds. Astronomers have identified more than 5,000 exoplanets, but they don’t know all that much about them. With Webb, Bean and his colleagues will be able to observe these far-flung planets in greater detail than ever, allowing them to uncover new truths about how planets, including our own, form and evolve — and someday, perhaps, to discover other habitable worlds beyond our solar system. Maybe even another planet like Earth.
“The technology that we have
