Whew! Asteroid collision delayed 41 years, to 2071

The slim possibility that Earth could be struck by a speeding asteroid in the year 2030, reported by astronomers last Friday, has now disappeared. As with at least two previous reports of possible impacts, astronomers discovered new information less than 24 hours after issuing their warnings that proved there would be no collision that year.

But in this case, the possibility of a collision was just postponed, rather than eliminated. The new information shows there is still one chance in 1,000 that the small asteroid, called 2000 SG344, could strike in the year 2071, astronomers reported over the weekend.

"The new calculations have ruled out the 2030 event," said Don Yeomans, Paul Chodas and Steve Chesley of NASA's Jet Propulsion Laboratory. But, at the same time, the group said, "they have also increased the likelihood of encounters in years after 2030." The first such possibility occurs on Sept. 16, 2071.

Astronomers are still feeling stung by the ups and downs of past reports of possible asteroid collisions at least twice before; they have had to revise their predictions less than 24 hours after the initial reports, after new information turned up. The first such case, involving an asteroid called 1997 XF11, triggered screaming headlines in newspapers and magazines around the world and was seen as an embarrassment for astronomers when old photographs uncovered the day after the initial report showed there would not be an impact after all.

This was, in fact, just the kind of result some of the astronomers had hoped for: The wave of publicity generated by the initial report was what motivated astronomers to go check their old pictures for earlier images of the asteroid that would allow a more accurate calculation of its orbit, and solved the mathematical problem. But the result was a major image problem for astronomers instead. While the changed prediction was really a result of new information, it was widely perceived as simply having been a botched initial calculation.

Indeed, Discover magazine, a mass-market science magazine, recently included the 1997 XF11 affair in a list of the 20 worst scientific debacles of the past century.

Ever since, there has been an ongoing heated debate among astronomers about how best to handle the disclosure of such predictions, with finger-pointing about who was to blame for the embarrassing outcome.

But astronomers fear that if they withhold information about a possible impact long enough to make a solid confirmation, the public might complain about a cover-up.

One result of all the debate was that the International Astronomical Union drew up guidelines about how such discoveries should be handled. The guidelines call for a three-day waiting period after any initial calculation showing the possibility of an asteroid striking the Earth.

The delay is meant to provide time for other scientists to make independent calculations and confirm that no error has been made.

Ironically, last Friday was the first time the new guidelines have been implemented in a real case -- and the result was almost exactly the same as before. Less than a day after the report went out, an astronomer found old photos that eliminated the chance of an impact on the stated date.