It wasn't the first time someone shouted "Asteroid!" and then quickly had to take it back. In 1989 a badly translated American wire service story prompted Chinese news telecasts to sound a false alarm about an imminent impact. Three years later Comet Swift-Tuttle was predicted to come perilously close to Earth in 2126, until a recalculation showed no threat after all.
Now, in 1998, here was Brian Marsden of the Harvard-affiliated Central Bureau for Astronomical Telegrams in Cambridge, Mass. astronomy's record keeper and unofficial town crier warning of a possible smashup in our lifetime. As it turns out, the mile-wide rock known as 1997 XF11 will miss us by a comfortable 600,000 miles in 2028. We only know that because Eleanor Helin's asteroid search team at NASA's Jet Propulsion Laboratory (JPL) went to the team's archive and discovered an 8-year-old image of the object within 24 hours of Marsden's March 11 alert. Using the new data, Marsden and others made a more precise determination of its orbit. No apocalypse.
The first thing asteroid researchers want you to know is that they're not a bunch of bumblers. David Helfand, a Columbia astronomer, agrees. "Nobody did anything wrong," he says, at least not in a scientific sense. Nor did the press get the story garbled. True, says Helfand, three of the seven network TV crews that visited his office asked whether this was really a Hollywood plot to hype two coming asteroid disaster movies. But by and large, says Benny Peiser, an anthropologist at Liverpool John Moores University in England, who runs an electronic forum for scientific discussion of the asteroid threat, the press behaved in a "very rational and very considered way."
So why are scientists who study asteroids for a living so upset? And why, weeks later, were many of them still sending out acrimonious e-mail blaming each other for the Great Asteroid Scare of 1998?
Reason #1: What was normally a private, unhurried scientific process suddenly became very frantic and public. Marsden's official IAU Circular 6837 gave his estimate of how close the asteroid would come to Earth and encouraged other astronomers to make additional observations to help reduce the uncertainty. All standard procedure. But the circular was followed by a press release that reached a much wider audience of reporters, virtually ensuring that the story would make worldwide headlines the next day. Most asteroid researchers, even those who say Marsden is unfairly blamed for crying wolf, say the press release, which specifically mentioned the remote possibility of an Earth collision (the circular hadn't you would have had to do the calculation yourself), was a mistake. Marsden, a likably droll Briton, admits that the press release part of his strategy "needs rethinking."
Leif Robinson, editor-in-chief of the popular astronomy magazine Sky and Telescope, has known Marsden for something like 40 years, but chides him and the rest of the asteroid research community for an "incredible naïveté" when it comes to public relations. Each and every day [asteroid researchers] hunt for objects that could put an end to the world as we know it. But, says Robinson, "Nobody thought about what happens if [the search] is a success."
Reason #2: Rivalries within the asteroid community made matters worse. Only a handful of people worldwide do the kinds of calculations necessary to determine asteroid positions 30 years hence. Before Helin dug through her old photos in response to Marsden's request, all but one team headed by Don Yeomans at JPL agreed that the chances of 1997 XF11 hitting Earth were small, but not zero. When Helin produced her images, Yeomans cranked out his own press release saying the chance of a collision was now officially zero. Many reporters were left with the idea that JPL researchers had somehow corrected Marsden's faulty calculations even though the Harvard group posted its own revised estimate within 90 minutes of Yeomans'. Marsden is still bitter, and many in the asteroid community agree that Yeomans' action gave an erroneous impression of disagreement when none existed.
Less than a week later, NASA, which funds the two largest asteroid searches now under way, asked the squabbling scientists to play nicely together, and next time to confer among themselves before sounding a public alarm. But not everyone is convinced that an official party line is a good idea when it comes to asteroid warnings. For one thing, says Marsden, it's an international concern, not just NASA's. Peiser agrees: Even if a false alarm is messy and embarrassing, "the more it happens in the public, the better."
Besides, the public didn't seem all that terrified anyway, and many editorialists played the episode for laughs. The New York Post ran its usual screaming headline, "KISS YOUR ASTEROID GOODBYE," and asked nine Ordinary Citizens: "If the asteroid were to hit Earth tomorrow, what would you do today?" Two-thirds said they would get drunk.
If it ever happens, they may not have the time. David Morrison of NASA's Ames Research Center, who headed a 1992 NASA study of the asteroid threat, points out that because 90 percent of dangerous asteroids are still undiscovered (due in part to stingy government funding for ground-based searches), the most likely warning we'll get is none. "The first we would know of the danger," he speculates, "is when we saw the flash of light and felt the ground shake." --Tony Reichhardt
Asteroid 1997 XF11
Clark R. Chapman, Papers & Preprints on Near-Earth Asteroids and the Impact Hazard, Southwest Research Institute, Boulder, CO
Near Earth Asteroid tracking homepage
Background material on Jupiter, comets, and 1994 collision of Jupiter with Comet Shoemaker-Levy, Hawaiian Astronomical Society
View of the Solar System, Calvin J. Hamilton, Hawaiian Astronomical Society
Probable meterorite impact at Tunguska, Russia, 1908
Near Earth Asteroid Prospector mission, Space Development Corporation
American Astronomical Society
Closest Approaches to the Earth by Minor Planets, Minor Planet Center, Smithsonian Astrophysical Observatory
Resources on comets in The Net Advance of Physics, The Internet Pilot To Physics (TIPTOP), MIT/Athena University
Asteroid and Comet Impact Hazards, NASA Ames Space Science Division
TONY REICHHARDT writes about the space program for Nature and Air & Space/Smithsonian.