by Kathy Sawyer
Last week’s global dress-rehearsal for Armageddon (which has now been indefinitely postponed) “should serve as a wake-up call,” said astronomer Daniel W.E. Green, who works at ground zero—the Cambridge astronomical clearinghouse that first informed the world that a mile-wide asteroid would be bearing down on Earth in 30 years, with the slight chance of a catastrophic collision on Oct. 26, 2028.
But that wake-up alarm has jarred astronomers almost as much as it has shaken unwary Earthlings who have gone about their lives largely unmindful of the fact that Earth exists in a cosmic shooting gallery, in which collisions are a fundamental force of nature.
Astronomers who know the most about the subject last week found themselves overwhelmed by the public reaction and an unanticipated round-the-clock international media blitz that sometimes got in the way of the emerging facts of the story. Though most say the scientific process worked just as it should in this case, the astronomers are discussing better ways of handling the public relations aspects of the next discovery of a potential killer rock from outer space.
The public drama began late Wednesday when Brian Marsden, a recognized master at computing orbits from preliminary data, issued a statement that was circulated not only to astronomers but to the media on the Internet, saying that 30 years from now “it is virtually certain” that the asteroid would pass within the moon’s distance (less than 250,000 miles), probably much closer, and that there was a slight chance it could actually strike the planet. What got peoples’ attention was the size of the object. At a mile wide, it was by far the largest object in modern times ever to pass so close to Earth. Any impact would cause widespread destruction and global ecological damage.
Marsden’s provocative prediction last week was based on observations spanning the three months since the asteroid was first detected. The observations were made by four independent groups of astronomers around the world, using different computer software to come up with similar results, said Green, Marsden’s associate.
It never occurred to the IAU team not to put the word out at once, he said. “We’re the world clearinghouse. Our job is to get the word out to astronomers” who want to do follow-up observations. We actually get criticized [in the astronomical community] if we hold onto anything too long.”
Marsden directs the International Astronomical Union (IAU) of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Through its Central Bureau for Astronomical Telegrams, his small staff handles tens of thousands of observations of astronomical objects each month, and Marsden “does a thousand or a million times more orbit computations” than any other expert in the field, Green said.
“We had no clue that the media would react the way they did,” he said.
The good news on Thursday was that Marsden’s alert had its intended effect, which was to mobilize the astronomical community to search old records, make new calculations and plan more observations, so that the worrisome asteroid’s future trajectory could be further refined.
The bad news was that, by the time new calculations from researchers at the Jet Propulsion Laboratory in Pasadena showed unequivocally that the asteroid had “zero chance” of hitting Earth, Marsden and his staff were already locked in a day-long marathon of television interviews. He learned about the new prediction belatedly, from reporters inquiring about the JPL press release. The result was a period of confusion and, Green said, “It sounded like we didn’t have our act together.”
The big breakthrough had come overnight Wednesday, when veteran asteroid watchers Elinor Helin and Ken Lawrence, of JPL, found previously unreported images of 1997 XF11, which had then appeared uninteresting, in a search of archived photographic plates from observations they had made at Palomar Observatory in 1990.
The new data were handed over immediately to Donald K. Yeomans and Paul W. Chodas, ace JPL comet and asteroid trackers who calculate trajectories for NASA spacecraft rendezvous and who correctly predicted the outcome of a collision between a comet and Jupiter in 1994. They had already begun to challenge Marsden’s initial prediction, saying the asteroid would not come so close to Earth.
By late Thursday, Yeomans and Chodas had incorporated the new data from Palomar. Where before there had been only three months of observational data, they now had tracking information about the asteroid’s course over a period of eight years. The new data showed the asteroid would pass well beyond the distance of the moon.
Marsden and his staff were taken aback by the new calculations, Green said, but as soon as they had confirmed them with additional data from Helin, he said, “There was no debate, of course not. ... We never disagreed. We quickly threw [the JPL calculations] into our own [computer] program and saw that the closest approach moved out to 600,000 miles.”
But a number of print and broadcast news reports late Thursday and into Friday said there was a “debate” or a dispute among astronomers about the asteroid’s future path.
It is an unfortunate necessity that the scientific process often plays out in a manner that, to the public, appears confused, Chodas said. But when a cosmic object threatens to collide with Earth, “that’s a special case.” Next time this happens, he said, many in the astronomical community would like Marsden to share the data with them before he shares it with the public. “The peer group of astronomers need to digest the data and quickly come to a consensus,” Chodas said.
Actually, according to astronomer Stephen Maran, a spokesman for the American Astronomical Society (AAS), Marsden had not intended to release the news so widely, so fast. But Maran talked him into letting the AAS put it out over the Internet, to spread the word as fast and fairly as possible.