Space Scientist: Geoff Marcy and Paul Butler

The Astronomers Who Proved Carl Sagan Correct

By Joseph DAgnese
Nov 9, 2003 6:00 AMNov 12, 2019 5:14 AM


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Thirteen state-of-the-art telescopes stand on Mauna Kea, the tallest mountain in the Pacific basin, looming over the island of Hawaii. By day the view from the peak is of a rich blue black sky. By night, the pitch darkness is studded with starry diamonds. At nearly 14,000 feet, the mountain offers an untainted view of the heavens that is increasingly rare in a lit-up world, a view that makes an astronomer’s work a lot easier.

Photograph by Amanda Friedman

Geoff Marcy (left) and Paul Butler are reflected in a mirror segment from the Keck I telescope, which they use to find extrasolar planets. “We’re lucky we don’t have any children,” says Marcy. “Our kids are the planets.”

Late on a Saturday night, Geoff Marcy and Paul Butler are hunched over computer monitors in an office 12,000 feet below the summit, in the nearby ranching town of Waimea. People turn in early here, but Marcy and Butler—who, in their 16 years of planet hunting, have found 61 of the 77 planets outside our solar system that are recognized by astronomers—call themselves vampires. From 7 p.m. to 6 a.m., with the help of graduate student Jason Wright, they preside over a series of workmanlike photo shoots. Again and again they point Keck I, the world’s largest telescope, at one of the stars on their hit list and shoot. They do this until they’ve captured the light of 100 or so stars that interest them. A spectrometer splits that light into its component colors from red to violet, generating a rainbow image so complex that it can be analyzed only by computer.

Extrasolar planets are too faint to be seen, even with Keck. So Marcy and Butler must infer their presence by studying how stars are affected by the gravitational tug of planets around them. Although a star may be thousands of times more massive, a smaller planet’s pull can cause it to wobble. Early in their careers, the duo spent seven years writing software that would let them nail down the wobble with accuracy. Now they can detect a wobble of a celestial body as slow as three meters per second, about the speed of a bicycle in motion.

The magic hour has just arrived when data from the previous night’s viewing start streaming back from Marcy’s computer in Berkeley and Butler’s machine in Washington, D.C. The computers have crunched the numbers overnight and plotted the data on graphs depicting the shape and period of each planet’s orbit. “This is a pretty one!” yells Marcy, 48, enthusiastic despite the dark circles under his eyes.

He turns to a visitor. “That’s a new planet, known only to the three of us in this room, and now you.” Butler, 43, a hulking man in a Hawaiian shirt, shorts, and sandals, looks over his shoulder and says, “Tell anyone and we’ll have to kill you.”

Marcy is small and chatty, Butler huge and less talkative. They grew up in Southern California, a few miles and years apart. Marcy’s parents gave him a map of the solar system and a telescope, which he used to plot the orbit of Saturn’s moon Titan when he was only 14. At the same age, Butler built his own eight-inch telescope; he was fascinated by the tales of what had happened to astronomers like Galileo, the first person to use a telescope to make astronomical observations, and Giordano Bruno, who dared to dream of multiple worlds and parallel universes. Galileo ended up under house arrest, and Bruno was burned at the stake. “Wow,” Butler remembers thinking, “this is wild, rock-and-roll stuff. The powers that be are threatened by it!”

When Marcy first decided to look for planets outside the solar system, the powers that be were as skeptical as they have always been. “If you mentioned this to people in the 1980s, they looked down at their shoes and scuffled their feet,” Marcy says. “The problem with planets was that they didn’t shine. So how could you study what you couldn’t see?”

Marcy figured he couldn’t lose. Only 28, he already felt washed up in a science world that expects startling discoveries before age 25. His work on the magnetic fields of stars was going nowhere. He was seeing a therapist to combat depression. One day in the shower, it hit him: “If I want to succeed at this, I need to answer questions I relate to on a gut level. I need to investigate things I cared about as a 7-year-old. I really wondered if there were other planets out there.”

From the start he knew that any serious planet-hunting endeavor would rely on analyzing minuscule shifts in starlight. These changes indicate when a distant sun is wobbling toward or away from Earth. Wobbling is hard to detect because telescopes and spectrometers, no matter how precise, alter subtly with temperature and use. To look for planets, Marcy had to filter out the errors that would inevitably crop up in the images he’d get back from the spectrometer.

That’s where Butler, then a graduate student, came in. The two met at San Francisco State in the mid-1980s, where Marcy was teaching and Butler was finishing a bachelor’s degree in chemistry and a master’s in astrophysics. Taking up Marcy’s challenge, Butler auditioned chemicals that were known to absorb light at precise wavelengths. He was searching for one that was safe and stable, a rare combination. A Canadian team had tried hydrogen fluoride because it absorbed light at a large number of discrete wavelengths in the visible spectrum. However, it had proved not nearly precise enough, and a whiff of it could kill. After six months in the lab, Butler emerged with harmless iodine gas, which absorbs light at even more wavelengths. More absorption allowed greater precision, and the pair could use the result to calibrate their data.

But first Marcy and Butler had to get access to the stars. Because astronomers are granted access to telescopes according to their stature in the community, at the start they had to beg just to get the worst nights on the least powerful scopes. After they announced their first finds in 1996—six extrasolar planets—and ended up on the cover of Time, they moved to the head of the pack. Now they have the run of the world’s best facilities.

Since that first announcement, the duo has found more than three-quarters of the known extrasolar planets, the first solar system outside our own with multiple planets, the first extrasolar Saturn-size planet, and the first extrasolar planet that transits between Earth and its sun, causing the brightness of that sun to flicker. But “people don’t realize that when we announce new planets, we’re scared,” says Butler. “Planets are like clockwork. If you make a prediction that this planet’s going to be there and behave a certain way, you’ve got to be right. If it doesn’t, you lose your credibility.”

That has never happened. The two have been known to sit on their data for years, waiting until they know they are right. “We owe it to our fellow humans to pour the planets out,” says Marcy. “But we’re very conservative. Some of these are not fully cooked yet. We can’t take them out of the oven. We live in an age where the credibility of scientists and politicians is challenged often.”

They know most people have anthropocentric questions about extraordinary worlds: Does anyone live out there? Can we go there someday? All reasonable questions, says Marcy. “Why, in the shower, did this idea grab me? The answer is evident to any 6-year-old. We cherish this Earth. It’s our cosmic home. The child, the nonprofessional in me, understands why we are interested in other abodes. If we diversify cosmically, our presence is more secure. We’re vulnerable being on one rock. I think what Paul and I are doing is finding ports of call where we can go someday and, in a sense, drop anchor.”

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