Brave New Worlds

Columbia astronomers are going beyond our solar system to understand exoplanets, find exomoons, and explore all sorts of surreal estate.

by Bill Retherford '14JRN Published Winter 2017
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This artist's concept shows the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to our solar system. Proxima b orbits in the habitable zone, where the temperature is suitable for liquid water to exist on its surface. / Photograph by ESO / M. Kornmesser

Discovering the first exomoon would surely be a spectacular find. But nobody will be startled. Exomoons, like exomountains, are expected. Stranger things have already been seen. “Look at the exotica coming out of exoplanets,” says Kipping. Hot Jupiters like TrES-2b (gargantuan, superheated, typically ten times closer to their stars than Earth is to the sun) are ubiquitous. “And nobody expected to find them,” he says.

Astronomers once thought our solar system was a template for the rest of the galaxy. Every inference about exoplanets was built on it. “But our solar system,” says Kipping, “is not typical.” With eight major planets and millions of asteroids, the solar system covers ten trillion miles. Yet compact systems seem more common. The seven TRAPPIST-1 planets, discovered this past February, are crammed in space; they occupy a congested area of barely six million miles — one-sixth the distance between the sun and Mercury, its closest planet.

About half the exoplanets have wildly eccentric orbits. But in our solar system, the planets’ orbits are basically elliptical; Earth’s is almost a circle. Our sun is categorized as a yellow dwarf star, middle-aged and relatively hot; but three-quarters of stars are red dwarfs — “older and dimmer,” says Kipping, and often one-tenth the size.

Hardly an analog to the rest of the galaxy, our solar system is actually an anomaly. “We’re not the freak of the universe — but we are a very poor approximation,” Kipping says. To Cool Worlds researchers, that might be the most startling discovery of all.


When astronomy was first taught at Columbia University (then King’s College) in 1754, little was known about the planets. The British astronomer William Herschel wouldn’t find Uranus for another twenty-seven years, and Neptune’s reveal was ninety years away. Telescopes surveyed land more frequently than stars. In 1776 George Washington, then the Continental Army’s commander in chief, supposedly persuaded the College to loan him a telescope — the school’s only telescope — as a way to monitor British troop movements during the Battle of Long Island. Washington promptly lost both the telescope and the battle. There the story ends, and it may be apocryphal anyway. Whether Washington ever wondered about exotic worlds or extraterrestrials is unclear. But John Adams, Washington’s presidential successor, did. The universe, he said, is “both infinite and eternal,” and at twenty — almost the age of the Cool Worlds graduate students — he wrote this in his diary: “All the unnumbered worlds that revolve around the fixed stars are inhabited.”

Well, surely not all. But some? “I would be shocked if life was not elsewhere in the galaxy,” says McTier. Concurs Sandford: “The odds of us being the only planet with life are kind of ridiculous.” Jansen remembers a Caribbean vacation at age nine: “My mom goes, ‘You’ve got to come outside and see the stars.’ I’m like, ‘Oh, fine.’ And then I saw this dome of stars. There were so many. I just looked at them — and then I thought, if every one of those stars has planets, there’s no way we’re the only living creatures in the universe. That was very specifically the moment I thought astronomy was amazing. I’ll never forget it.”

Space theoreticians have long ruminated on exoplanet landscapes. They simply calculate a planet’s density and then take a smart guess.

Of the trillion or so exoplanets estimated in the Milky Way, about 10 percent — one hundred billion — may hold water and reside in the habitable zone. Any life out there might scale from primordial microbes to technologically advanced aliens. “You’re looking at vast opportunities for life,” says Kipping. How much, what kind, where located? “I can’t even speculate,” he says. “There’s just no information to go on. Working with a single data point, we are completely stuck.” That single data point is us. Earth is the only example of life anyplace.

Although there’s now Proxima b, an exoplanet discovered in August 2016 and a potential analog of Earth — about the same size, in the habitable zone, and as a bonus, only four light years, or some twenty-four trillion miles, away. Celestially speaking, that’s just across town. Cool Worlds researchers, captivated by Proxima b, are contributing to Breakthrough Starshot, the initiative founded by the celebrated physicist Stephen Hawking and Facebook CEO Mark Zuckerberg. The proposed project is an outrageous venture: somehow develop and ultimately dispatch an uncrewed nanocraft to snap flyby photographs of Proxima b. The preferred cruising speed for the probe is approximately 37,200 miles per second, one-fifth the speed of light. Travel time should be twenty-one years. Getting the probe ready to go could take at least that long. But imagine what might be in those photos. Oceans? Vegetation? City lights? Not much of anything? Who knows. “There’s a chance,” says Kipping, “that when I’m retired I might see a photo beamed back.” That image could forever change the way we see not only the exoplanets, but ourselves.


Read the related article entitled Picturing Planets:

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