Mirror Earth by Michael D. Lemonick Page A

for brown dwarfs, objects bigger than planets but smaller thanstars. A brown dwarf could be as much as eighty times as massive as Jupiter before it would start fusing hydrogen into helium in its core—the same reaction that powers an H-bomb, and the one that makes stars shine. At this point, brown dwarfs were purely theoretical (they’ve since been shown to exist), but looking for them had made Mayor an expert on radial-velocity measurements too. The e-mail said, in part, “This is interesting—the minimum mass is well under the stellar limit. It could even be a giant planet.” By the time Latham hit “send,” the clock had ticked past midnight. It was now April 1, and he was a little bit worried that Mazeh and Mayor might think it was an April Fool’s joke.
    But Mayor went out and did his own measurements, and got the same results. Mayor also determined that whatever this object was, its orbit was eccentric—it was somewhat oval rather than nearly circular. That ruled out a planet, because, as Latham said, “everyone knew that giant planets had to have circular orbits.” Everyone also knew you couldn’t have planets bigger than about twice the mass of Jupiter. And with a “year” just eighty-four days long, well, said Latham, “that was just a killer. Three strikes, you’re out! Tsevi and I had a bet—we still do, in fact—I said it was a small star, he insisted it was a big planet.” When Latham, Mayor, Mazeh, and two others reported the discovery in
Nature
on May 4, 1989, they wrote: “The companion is probably a brown dwarf, and may even be a giant planet.” Latham told me Mayor “wasn’t too happy with that wording.” He was on Mazeh’s side.
    In any case, Latham was too busy with other things to keep looking for objects like this one, but Mayor, he says, “pickedup [the project] and ran with it.” Like Marcy and Butler, he and a French instrument builder named Andre Baran began beating down the errors in their own spectrograph. Marcy and Butler had chosen to do it with iodine cells and horrifically complex software. Mayor and Baran chose instead to make their spectrograph as utterly stable as they could. They used a reference spectrum from a lamp outside the telescope, but they piped it into the spectrograph with fiber-optic cables in such a way that it was as undistorted as it could possibly be.
    When they’d done everything they could think of, Mayor told me at a conference on the Isle of Capri in 1996, they had beaten down their errors to thirteen meters per second, or about 30 mph. They couldn’t find a Jupiter like the one in our solar system, but then, they weren’t looking for one. Mayor still cared mostly about brown dwarfs, and the spectrograph, far more sensitive than Dave Latham’s, could detect them easily. In early 1994, Mayor and a graduate student named Didier Queloz began taking measurements of wobbly stars. By now, Marcy and Butler had been at it for half a dozen years.
    Mayor and Queloz had put more than a hundred stars on their observing list to maximize their chances of finding something. Brown dwarfs might be relatively rare, after all, and their orbits would have to be nearly edge-on for the astronomers to make a strong detection. Not all of them would be, of course. So the European astronomers began methodically ticking through their list. Within a few months, they noticed something very odd. A star named 51 Pegasi (the fifty-first brightest star in the constellation Pegasus) seemed to be wobbling, butin an impossible way. It was moving back and forth, not with a Jupiter-like rhythm of 11 years, not with an Earth-like rhythm of 365 days, not even with a cadence of 84 days, like HD 114762. This star was moving toward Mayor’s telescope and dancing and advancing again
once every four days
. If this motion were truly caused by an orbiting body, it was hugging its star an