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. Before publishing their report, Muller decided to get a second opinion from the fathers of the impact theory, Luis and Walter Alvarez. Neither conferred his benediction on the hypothetical star, but Walter recommended one way that its existence might be tested. He knew that if comets cyclically pelted the planet, they must have left behind craters in chronologically distinct batches. Water, wind and continental drift have eroded most of the earth's impact craters, but 100 of the largest survive in some form and have been roughly dated. Muller and Walter Alvarez examined the data on 13 of the best- dated craters spanning a period of 250 million years and, sure enough, the gutting seemed to occur in peaks of 28.4 million years (although the later inclusion of data from other craters made the pattern seem less conclusive).
The results of the crater analysis were published in the British journal Nature, right beside the Nemesis report. Coincidentally, that same issue contained yet another paper on the death star. It was from Whitmire, who had independently conceived of a companion to the sun.
Reviews for the Nemesis debut were what might be called mixed. Critics charged that so gigantic an orbit had never been recorded for two companion stars, and with good reason. If the sun and its presumed partner were actually three light-years (18 trillion miles) apart, they said, the gravitational attraction between them would be so feeble that a passing star or dust cloud would have bumped Nemesis out of orbit long ago, certainly before it could come back through the Oort cloud a dozen times. Says Shoemaker, who has been something of an impartial judge in the periodicity controversy: "I give this idea less than a 1% chance of being correct."
The warrior star, however, has captured the imagination of many others. Says Tom Gehrels, an astronomer with the University of Arizona: "When I heard the theory, I knew in my heart it was right." Indeed, Gehrels immediately hopped on a westbound plane to try to persuade Muller to let him help search for the companion. But Muller's own telescopic dissection of 5,000 stars in the Northern Hemisphere that are candidates for being Nemesis was already under way, and there was no need for Gehrels' help. So far, Muller has photographed nearly all the target stars once and is preparing to shoot them again in an attempt to detect some telltale movement.