(7 of 10)
Sniffing a connection, Rampino and a Goddard colleague, Astrophysicist Richard Stothers, among others, proposed an ingenious way that the oscillating journey might trigger bombardments on earth. Whenever the sun passes through the Milky Way plane, they suggested, the swirls of dust it encounters would gravitationally disrupt the Oort cloud, a vast bubble of comets that scientists believe surrounds the solar system at a distance of up to 10 trillion miles from the sun. Like a lazy fruit picker shaking plums from a tree, the dust would send showers of comets falling toward the sun. Some comets would collide with the planets, including the earth. Almost immediately, other scientists began tearing the Rampino-Stothers model apart. First of all, they said, the sun is pretty close to the middle of the galactic plane right now, and yet there has been no major extinction occurrence for millions of years (the last one apparently took place 11 million years ago, wiping out some marine protozoans and mollusks). More damning still, Physicist Patrick Thaddeus, also of Goddard, pointed out that dust clouds are so widely distributed that the Oort cloud should be encountering them practically all the time, not just once every 33 million years; some of the numbers his colleagues used in their calculations, he says flatly, are "just the wrong numbers."
Among the various astronomers who considered and promptly rejected the galactic carrousel notion was California's Muller, a scientist obsessed by periodicity. If a familiar cosmic mechanism could not account for the cyclic nature of extinctions, he decided, something completely different would have to do. During Christmas break in 1983, Muller and fellow Astronomers Marc Davis of Berkeley and Piet Hut of the Institute for Advanced Study in Princeton were brainstorming about stars and periodicity, when Muller noted that more than half the stars in the galaxy are thought to be binaries (pairs of stars that orbit a common center of gravity). Suppose the sun has a companion, he mused, and that companion was somehow disrupting the solar system's asteroid belt. Trouble was, he conceded, he could not come up with a convincing orbit for the companion. Suddenly the Dutch-born Hut interrupted him with an alternative suggestion: Why not make the companion star travel through the thickest part of the comet-filled Oort cloud, rather than the asteroid belt? Muller immediately saw that the problems he had had with asteroids disappeared when he substituted comets as the culprits. As he recalls, "We wrote the first draft of our paper that day."
The three realized that the sun's counterpart, if it existed, would have to be like no other companion star ever identified; it would travel in an enormous elliptical orbit three light-years across that would periodically take it farther from the sun than the distance between any known binary stars. Because it has not been identified in the four centuries since astronomers began using telescopes, it must be very small and dim, perhaps a red dwarf with one-third the mass and only one one-thousandth the brilliance of the sun. When it passed through the Oort cloud, it would dislodge a billion or more comets. Muller, searching for an appropriate name for the lethal companion, considered several. But the one that stuck was Nemesis, the Greek goddess who punishes the proud.