Mirror Earth (7 page)

Mayor and Queloz returned to the telescope, trying to make absolutely certain that they weren't somehow kidding themselves. Maybe the star was pulsing, its outer atmosphere bulging toward and then away from Earth in a four-day rhythm. Maybe the star wasn't perfectly spherical, and they were seeing the bulgy part moving toward them and then away. “The first principle [of science],” the physicist Richard Feynman said in a commencement talk at Caltech in 1974, “is that you must not fool yourself—and you are the easiest person to fool.” Peter van de Kamp had fooled himself with his “discovery” of a planet orbiting Barnard's Star (he fooled others as well; Otto Struve's 1952 paper refers to “results
announced … by P. Van de Kamp”). Mayor and Queloz, like Marcy and Butler half a world away, were determined to avoid destroying their reputations. But hard as they tried to make the impossible conclusion go away, it refused.

In the end, Mayor told me on Capri, “It's a difficult thing to decide you've done all you can, that you're ready to leave your office and go public.” They submitted a paper to the journal
Nature
claiming the discovery of a planet-like object they called 51 Pegasi b (the
b
meaning that it is a secondary object orbiting the star 51 Pegasi). Before the paper could be published, he spoke about the discovery at a conference in Florence, Italy, in October 1995. According to
Nature
's strict rules, he was allowed to do this, but he wasn't allowed to discuss the findings with reporters until the paper was actually published. If he did so prematurely,
Nature
wouldn't publish it after all—and
Nature
was prestigious enough that Mayor didn't want to flout the rules. There were reporters at the Florence conference who begged him for interviews. He politely refused, so they went ahead and announced the discovery without quoting the man who had made it.

In California, meanwhile, Geoff Marcy and Paul Butler began hearing about Mayor's find, first from colleagues who had been at the meeting, and then from reporters who were desperate to find an expert they could talk to. It seemed obvious to Marcy that Mayor had made a mistake. The sort of planet he was describing couldn't possibly exist. The theorists said so. Besides, Marcy couldn't possibly be scooped: He and Butler had been working tirelessly to find planets for six years now. How could someone else just stumble onto the discovery?

Still, he wasn't going to say Mayor was wrong without being absolutely sure. Astonishing things often turn out to be false—but not always. In 1989, for example, two chemists from the University of Utah claimed they'd discovered “cold fusion,” an inexpensive source of potentially limitless clean energy. I called Rob Goldston, the director of the Princeton Plasma Physics Laboratory, who was struggling to create fusion in a multibillion-dollar installation owned by the Department of Energy. “I don't know the details of the experiment,” he told me, “so I can't make any definitive statement.” “But,” he continued, making it clear as diplomatically as possible how he really felt about the claim, “if it's true, it means that everything we've learned about nuclear physics over the past fifty years is false.” In other words, Goldston was almost certain the chemists were wrong, but knew that an absolute statement might come back to bite him.

Marcy and Butler were convinced Mayor must be wrong. But maybe everything they knew about planets was false. Either way, they were all set up to find out for themselves. If Mayor's instruments could see this “planet,” theirs could too. To find a planet in a four-day orbit, you have to look at least once a day; Marcy and Butler had never bothered to look at any star more often than once every few months, because the wobbles they were looking for would play out over years. So they went up to Lick Observatory, where they'd already been approved for four nights on the 120-inch reflecting telescope. As the data streamed in from 51 Pegasi, they would immediately funnel it into their computers for processing, taking more data all the while.

After a couple of days, they knew Mayor was right. They'd been scooped by someone with a less sensitive instrument. Arguably, they'd been scooped by Dave Latham back in 1989 as well, but Latham's discovery had never been accepted as a planet, even by Latham himself. Ultimately, all the strikes against Latham's object would be eliminated as astronomers began to understand how strange planets really could be. In hindsight, Geoff Marcy now gives Dave Latham credit for the very first planet orbiting a Sun-like star.

Michel Mayor couldn't talk to reporters, but Marcy and Butler were under no such obligation, since they didn't have a paper about to come out. Reporters couldn't talk to Mayor, so they descended on the Californians. And while Mayor had made the discovery, Marcy and Butler
could
have made it. If luck had been on their side, they inevitably would have. So it was a sort of poetic justice that Marcy and Butler were the ones who ended up being lavished with public recognition. Geoff Marcy also realized that if they'd known how comparatively easy the universe would make it to find planets, they might not have worked so hard to make the Hamilton Spectrograph so precise. Their ignorance had put them behind, but it had given them an edge on future discoveries.

In fact, the discoveries had already been made, even if Marcy and Butler didn't know it. The astronomers had been searching for wobbles for many months now, returning over and over to a list of 120 stars. But they hadn't bothered analyzing the data, since they thought no star would show a perceptible wobble over so short a time. The information was just sitting in storage on magnetic tapes. Now that they knew such
a thing was possible, however, they realized the signals of planets might be on those unread tapes. Butler was “insane,” he later told me, to find out what was on them. He got his hands on some relatively fast computers and began feverishly processing data around the clock.

Within less than two months, Butler managed to tease out the signal of a planet orbiting the star 47 Ursae Majoris, in the Big Dipper. Then he found another, orbiting 70 Virginis, in the constellation Virgo. Neither of them was as crazy as 51 Peg b, as astronomers were now nicknaming it, but they were still closer to their stars than Jupiter is to the Sun. They were still a little crazy. 70 Virginis b, in particular, had an unusually eccentric, egg-shaped orbit. That was one of the strikes Dave Latham had listed against HD 114762.

Nevertheless, Geoff Marcy arranged to give a talk on their new planets at the winter meeting of the American Astronomical Society, which was coming up in a few weeks. Unlike Michel Mayor a few months earlier, he and Paul Butler didn't have a paper ready for publication, so they weren't bound to avoid reporters. They gave a heads-up to the society's press officer, an astronomer named Steve Maran, who immediately scheduled a press conference. He wouldn't say in advance what it would be about, although he told me privately, and undoubtedly told other reporters as well, that I'd be crazy to miss it.

Despite the veil of secrecy, however, word got out that Marcy would have something important to say, and when he finally did, he spoke with a theatrical flair that I would later recognize to be his trademark. “After the discovery of 51
Pegasi b,” he said, “everyone wondered if it was a one-in-a-million observation. The answer is … no. Planets aren't rare after all.” He went on to describe 47 UMa b and 70 Vir b. He also pointed out that the latter orbited in the habitable zone of its star, the region where water could exist in liquid form, the necessary ingredient for life. And while 70 Vir b itself was too big to support living beings (it's about six times as massive as Jupiter), it might have habitable moons. This was pure speculation, but it was a bold enough statement to get the discovery on the cover of
Time
and into headlines and news broadcasts around the world.

What all those viewers and readers didn't realize was that Marcy and Butler's announcement marked an enormous change in the way scientists would think about extraterrestrial life from that moment forward. For about two thousand years, philosophers and scientists had actively debated the question of whether life exists beyond the Earth. From the Renaissance on, it was widely believed that the answer was yes. But since the early 1900s, when astronomer Percival Lowell convinced himself that he could see canals and other evidence of life on Mars, thinking about and looking for life on other planets had been considered something of a fringe idea in science. The UFO craze that started in the 1950s didn't help.

In principle, scientists thought it was plausible that life existed elsewhere in the universe, and a few even tried looking for it—Frank Drake, who began the formal Search for Extraterrestrial Intelligence in 1961, for example, and a few NASA scientists who designed biology-sensing experiments for the Viking Mars landers in the 1970s. But no one even knew for
sure that there were any planets beyond the solar system for life to exist on, and it was clear to most astronomers that planets were just too difficult to find with existing technology.

Suddenly, because Marcy had ignored the conventional wisdom, and because Mayor had gotten lucky, it was clear that this simply wasn't true. It's something like what happened when the British athlete Roger Bannister ran the world's first sub-four-minute mile in 1954. Until he did it, many people thought it was impossible. Once Bannister showed otherwise, plenty of runners found that they could break four minutes as well. Those first three planet discoveries, considered impossible by many scientists, forced the entire field of astronomy to shift its perspective. Men and women who had gone to graduate school planning to study other topics changed direction and decided to look for planets instead. Senior astronomers who had spent their careers thinking about the Big Bang or the formation of galaxies did the same.

This influx of brainpower and of funding from NASA and other agencies led in turn to ingenious new ways to search, which turned up dozens, then scores, then hundreds of new planets, in such a bewildering array of sizes, shapes, and orbits that astronomers are still arguing, a decade and a half later, about how solar systems form and evolve. Even so, by the time Bill Borucki's lunch was delayed by an AP reporter's nagging questions in early 2011, no one had yet found a true twin of Earth—the likeliest place, given the admittedly little we know about extraterrestrial biology, where life might actually be found.

It wouldn't be long, though. And while many of the astronomers
working on the Kepler project had been inspired to go into planet-hunting by Geoff Marcy's and Michel Mayor's extraordinary discoveries in the 1990s—and even though Marcy himself would sign on as a project scientist with the Kepler Mission before the spacecraft launched—neither Marcy nor Mayor might end up playing a direct role in that discovery.

When Bill Borucki and Geoff Marcy set out independently to find worlds orbiting other stars, other astronomers were dubious only because it seemed obvious that astronomical technology wasn't yet sophisticated enough to find them. They had no doubt that such worlds existed. The almost universal attitude among astronomers, and among most other scientists who stopped to think about the question, was, “How could there
not
be planets around other stars?” The argument was both numerical and Copernican. The Copernican part refers to Nicolaus Copernicus, who showed in the 1500s that the Earth was not, as European philosophers believed, at the center of the universe. That discovery has now been generalized to argue that the Earth, and the Sun, and the solar system, and even the Milky Way galaxy, aren't special in any way that matters to the universe. If planets exist in our solar system, the Copernican principle suggests they probably exist around at least some other stars as well.

The numerical part comes from the fact that the Milky Way is made up of at least one hundred billion stars, and possibly
as many as three hundred billion. Most of the stars are smaller than the Sun—they're dim, red objects known as M-dwarfs—but even if you set those aside, tens of billions of stars very much like the Sun remain. It's possible that some of these are wandering through space unaccompanied by planets. It's impossible, or at least it seems very, very improbable, that all of them are.

When the question about planets arose thousands of years ago in ancient Greece, its meaning was a bit different. Nobody understood back then that the Sun was just another star, much closer to us than the rest. Nobody knew that the Milky Way, which split the night sky, was made up of billions of stars so far away that their light merged into a glowing band across the sky. For the Greeks,
world
and
cosmos
were interchangeable: The world included the Earth plus the sky and everything in it. So when the philosopher Epicurus wrote in the fourth century B.C. that “there are infinite worlds both like and unlike this world of ours … There nowhere exists an obstacle to the infinite number of worlds,” he was talking about what we would now call parallel universes, places forever inaccessible to us that would consist of a parallel Earth whose skies were dotted with glittering stars.

Epicurus and his rough contemporaries Democritus and Leucippus were known as “atomists,” because they believed the world and everything in it were made of tiny, invisible, and indivisible units they called atoms. These atoms, they argued, gathered together in different ways to form the stars, the Moon, the Sun, the planets, and the Earth, along with everything on it. When physical objects changed—the wood in a fire turning
into ashes, flames, and smoke; the wood in a tree growing larger and bulkier every year; the wood in a downed tree slowly rotting away—it was simply a matter of the atoms rearranging themselves into another form.

It all sounds impossibly modern, until you realize that atomism was a purely philosophical idea. The atomists had no evidence of any kind to support their assertions. They did no experiments that could test the hypothesis, so there was no way to refute it if it was wrong. That made atomism unscientific by definition, and it remained so until the early 1800s, when the English chemist John Dalton revived the idea to explain the nature of the chemical elements. Unlike the Greeks, Dalton and the scientists who came afterward did all sorts of experiments that could have demolished the atomic theory. The theory survived, obviously, although it wasn't fully confirmed until 1908 by the French chemist Jean Baptiste Perrin.