Mirror Earth (4 page)

He knew it couldn't be done with photomultipliers, the detector technology astronomers were using at the time. Borucki thought it might be possible to use CCDs, or charge-coupled devices, a sort of detector-on-a-chip that had been invented in 1969 at Bell Laboratories. CCDs are the detectors that have replaced film in modern digital cameras. At the time, though, they were rare and expensive. Astronomers were just beginning to adopt them. “Younger astronomers were familiar with CCDs,” he said, “but for the older ones, the attitude was, ‘If God wanted you to have CCDs you would have been … born with a CCD in your mouth instead of a silver spoon or … something like that.”

So Borucki and a couple of colleagues set up an experiment in the basement. “We built this thing with bricks and aluminum,” he said, “and we had a light shining under an aluminum plate with a bunch of holes in it.” Little holes were dim stars and big holes were bright stars. At first, the CCDs didn't seem to be sensitive enough to make the measurements he needed, but Borucki wrote a series of equations that corrected for the inaccuracies. “You can correct it out to ten parts, even one part per million,” he said, “even with a poor detector.” They'd shown, in other words, that they could find planets, and not just Jupiters but smaller planets as well—if someone would let
them try. But when Borucki tried to sell the project, he met with a brick wall of resistance. “You go to all sorts of meetings,” he said, “and you tell other astronomers, ‘You know, we can find other planets. We can find small planets. We can find them with a CCD.'” The other astronomers would say no, that's impossible. “They would get up and show why it couldn't be done. I would say, ‘We've done it. It can be done.' They would go to my boss and see if I could get taken off the project, because obviously we were wasting money, but he had enough faith in us that he let us continue.”

His boss evidently had faith to spare. The CCD experiments happened in the late 1980s, and in the early 1990s Borucki took his sales pitch on the road. He went to NASA with an official proposal for a space-based planet-hunting telescope. It was rejected. He addressed the agency's criticisms, and reproposed the mission. He was rejected. In all, Kepler was rejected four or five different times before the satellite was finally approved in 2000. It launched in 2009, a quarter of a century after Borucki's first theoretical paper in
Icarus
. Natalie Batalha, who is now Borucki's deputy principal investigator on the Kepler Mission, was in high school when he wrote the original paper. Now she has the office next door to his, and I visited her the day after I saw him.

“It really takes a unique person to create a mission like this,” she said. “Bill has this personality trait where negativity just rolls off of him. He doesn't accept it at all. I have never seen the guy take anything personally. You get rejected and they tell you, ‘This is bad for the following reason,' and he doesn't take it the way most people would. He could get a major rejection
in the mail one morning and in the afternoon still have the
cojones
to go to the administrators and ask for fifty thousand dollars to build whatever. Not many people can do that. It's incredible. It's been a pleasure to watch that and watch his positivity and persistence. It's been a life lesson for me. And it's a huge part of the Kepler story.”

By the time Bill Borucki was feeling the full force of press and public attention weighing down on him in 2011, Geoff Marcy had already been dealing with it for fifteen years. At this point, Marcy had been interviewed for literally hundreds—probably thousands—of newspaper and magazine articles, radio and TV shows, books and documentaries. Unlike Borucki, he seemed to relish all of it. Marcy invariably comes across in these interviews as engaging, relaxed, funny. He also comes across that way in person, at scientific lectures and public talks. He's given these by the hundreds as well, and they're hugely popular. He has a way of conveying the excitement of discovery and a sense of awe about the universe in an impressively informal, intimate way. He seems impossible to rattle. I watched him show up at a meeting of amateur geologists one night in the VFW hall in Orinda, California, only to learn that there was no extension cord anywhere in the building (no venue seems to be beneath him, as long as the audience is genuinely interested). He couldn't project his slides on
the screen, so he put a chair on top of a table, propped up his laptop, and mesmerized everyone in the audience even though most of them couldn't see much of anything.

Marcy is like the best teacher you ever had—warm, engaging, enthusiastic, funny, and ridiculously knowledgeable. Granted, he's got an unfair advantage over some scientists in commanding your attention, given that his area of expertise isn't, say, dung beetles, or the history of sheet metal. But he does have a way of explaining the search for planets—and, for the past decade and a half, their discovery—in a way that anyone can understand and appreciate. For his students at the University of California, Berkeley, he really is the best teacher most of them have ever had. During a visit to his office, I watched him stop and talk to a group of students, joking with them but also asking about their research projects, about which he seemed fully up to speed. I thought they were grad students; a senior professor at a major university wouldn't normally have a lot of contact with undergrads, except in groups of one hundred or more in a large lecture room. The professor certainly wouldn't know the students by name. But no—these were undergraduates whose mentor happened to be (until the Kepler Mission came along) the most prolific planet hunter in human history. He knew everyone's name.

This was not the future Geoff Marcy would have imagined for himself when he was starting out in astronomy. In 1983, the same year Bill Borucki wrote his first paper on searching for planets, Marcy found himself sinking into a depression. He was more certain every day that he would never make it as an astronomer. You wouldn't have guessed it by looking at his résumé: undergraduate degree in physics and astronomy from UCLA; Ph.D. from the University of California, Santa Cruz; postdoctoral fellowship at the Carnegie Observatories, in Pasadena, California—the same prestigious institution where Edwin Hubble discovered the expanding universe, and where countless other astronomical superstars have worked.

Geoff Marcy
(C. Rose)

But that was the trouble. Marcy's sense of self-doubt had begun in graduate school, where some senior astronomers had criticized his dissertation on magnetic fields in stars. “I didn't have any confidence in my own ideas,” he recalled during a conversation in the mid-1990s. “I was in a depression. I was convinced I was an imposter, that I didn't belong with all of these high-powered people.” At Carnegie, which took only the very best of the best, they were even more high powered. They'd taken him as well, of course, but Marcy was sure they'd made a huge mistake. Everyone around him was brilliant, he could see that easily enough. But it was clear to him that he simply wasn't smart enough to be an astronomer.

One morning, Marcy hit bottom. Here's how I described it in my 1998 book,
Other Worlds
:

Marcy dragged himself out of bed and into the shower as usual, but instead of turning off the water when he was finished, he just stood there thinking. He knew he had to get himself out of what had become a perpetual depression. “I'm not Einstein,” he thought. “I'm never going to be. So what am I going to do—beat myself up over it for the rest of my life?” He recalled how as a kid he had had posters of the planets plastered on the walls of his bedroom and had
stayed up half the night for the pure joy of exploring the universe through his telescope and then he sat glued to the television to watch humans take the first steps on the Moon in July 1969. If he could somehow reconnect with the sense of wonder he had felt back then, he might be able to get excited about astronomy again. “I have to find something to work on,” he told himself, “that addresses a question I care about at a gut level.” It also had to be something difficult to do. There wouldn't be much satisfaction or self-respect in solving an easy problem.

All of this went through his mind while the hot water poured down his back, and while it seems a bit too romantically tragic to be true—and while Marcy does have a flair for the dramatic—I believe it. He had no inkling of what Bill Borucki was doing at just about the same time at the Ames Research Center, several hundred miles to the north. But Marcy decided to take on the identical challenge. He knew, as Borucki did, that the question of whether other worlds existed out among the stars had held the imaginations of philosophers and scientists for thousands of years. Reconnecting with his sense of wonder would not be a problem.

The search for distant worlds would also meet his other requirement: It would be extraordinarily difficult to do. Like Borucki, he knew about astrometry—measuring the back and forth wobbles an orbiting planet would impose on its host star. His instinct was the same as Borucki's: Those measurements would be so hard, and the technology required so complex and expensive, that it might be decades before it ever happened, if
it happened at all. Unlike Borucki, however, Marcy didn't choose to look for the dimming of stars as planets transited in front of them. In fact, he told me nearly thirty years later, “Transits never even occurred to me. I never thought about them at all.”

That's not especially surprising. Borucki was an expert in measuring light, so he decided to search for planets with a technique that required high-precision light measurements. Marcy's career had had mostly to do with breaking light apart to see what it could reveal about the star that was emitting it. The formal name of this process is spectroscopy, and it's been a staple of physics and astronomy since the 1800s. Its roots go back even further: Chinese scholars suggested as far back as the 1000s that rainbows were created when drops of water in the air split sunlight into a spectrum of colors. Persian and Arab astronomers came to the same idea independently, and in the 1200s the English natural philosopher Roger Bacon experimented with glasses of water and crystals that split light just as a rainbow does. Isaac Newton used prisms to split sunlight as well. William Herschel, who won worldwide fame for his discovery of the planet Uranus in 1781, did his own experiments with light and color that led to his discovery of infrared light in 1800—the first hint that light comes in colors the human eye can't perceive.

Physicists now understand that light comes
mostly
in colors we can't see. If you think of light as a piano keyboard, with each note representing a color, you can think of the visible spectrum as the octave right in the middle. Infrared is lower in pitch than visible light. Microwaves are lower still, and radio
waves are the deepest bass notes. At the other end of the keyboard, ultraviolet light is just a little too high in pitch for us to see. Gamma rays are higher, and X-rays still higher—the shrill, tinkly notes at the far right. (Like most analogies, this one isn't perfect. There are vastly more colors of light, most of them invisible to us, than there are notes on a piano).

The Sun shines in virtually all of these colors, at least to some degree. We can see only the colors of the visible-light rainbow because these are the colors that penetrate our atmosphere most easily. We evolved to take maximum advantage of the kind of light that's most available. If we want to see at night, when there's no sunlight, we can put on night-vision goggles that are sensitive to infrared light. Living things, including plants and people, glow in the dark, but mostly in the infrared. We've also invented technologies for sensing ultraviolet, microwaves, gamma rays, and all the other colors of light. When astronomers began using these, in the 1920s, they began finding all sorts of cosmic phenomena they'd never imagined before—including, in 1965, the light left over from the Big Bang, which is now detectable only as microwaves. Ultraviolet astronomy, X-ray astronomy, radio astronomy, and gamma ray astronomy are now distinct, though obviously related, branches of science.

In the early 1800s, William Hyde Wollaston, an Englishman, noticed that fine, dark lines interrupted the artificial rainbows he had created with prisms. A German chemist named Josef von Fraunhofer independently discovered the same thing. Within a few decades, chemists understood that the lines were caused by chemical elements in the Sun's outer layers. The
elements absorbed very specific colors of light on their way from the Sun out into space. The elements are like filters. They catch
very
specific colors, so not just “blue” but “the exact color of blue represented by a particular wavelength of light.” That's how specific we're talking about. A given element or compound doesn't just absorb light at a single wavelength, but at many different wavelengths at once. It's like a bar code, with a pattern unique to each substance. If light is shining through many different elements or compounds at the same time, the multiple overlapping barcodes have to be untangled before you can figure out what you're looking at.