If the world comes to an end in 2044, it won't be because of asteroid 1999 AN10, a kilometer-wide rock that caused a media sensation earlier this year (ScienceNOW, 20 April 1999). Professional astronomers have debated the chances of the asteroid hitting Earth since its discovery in January, but thanks to some diligent searching by two German amateurs, the world can rest assured. The "doomsday asteroid" is harmless.
Initial calculations by Andrea Milani of the University of Pisa and his colleagues hinted at a small but nonzero possibility that the rock would slam into Earth--with apocalyptic consequences--in 2039, following a close encounter on 7 August 2027. In May, further observations by Australian amateur astronomer Frank Zoltowski seemed to worsen the odds; based on his photos, astronomers at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, predicted a 1 in 500,000 chance of an impact in 2044.
From their home in Berlin, amateur astronomers Arno Gnädig and Andreas Doppler recently searched through the Digital Sky Survey, a set of photographic plates obtained at Palomar Observatory in California in the 1950s, which have been digitized and made publicly accessible through the Internet. Last Sunday, they discovered the asteroid's trail on a plate taken on 26 January 1955, says Gnädig. On Monday, after carefully checking their results, they reported their discovery to the Minor Planet Center in Cambridge, Massachusetts, where astronomers Brian Marsden and Gareth Williams used it to calculate a new orbit. The revised path makes it clear that the close encounter in August 2027 will never happen, and 1999 AN10 won't pose a threat for many decades to come, says Marsden. "We were a little bit surprised," he adds.
Gnädig points out he and Doppler wouldn't have been able to find the trail if Marsden and Williams hadn't calculated a revised orbit based on Czech and Australian observations only weeks ago. "We were just lucky," says Gnädig. Indeed, Donald Yeomans and his colleagues at JPL recently carried out an automated search of the Palomar plates, and came up with nothing. "Either our search constraints were too tight, or the image was too faint," says Yeomans.
The discovery goes to show, says Marsden, that "there are many great amateurs out there doing wonderful work for us." David Morrison of NASA's Ames Research Center agrees. "[This field] has always been a partnership between professionals and amateurs," he says.