2003 was the first year that astronomers spotted fewer killer asteroids than the year before, an encouraging sign that recent efforts to catalogue the most dangerous objects are bearing fruit.
Worried that a killer asteroid might go unnoticed until too late, the US Congress in 1990 gave NASA the job of finding 90 per cent of all near-Earth asteroids larger than one kilometre across by the end of 2008. Since then, the number of new discoveries has increased as new search projects come online. In 2001, the Spaceguard project found 89 objects, and in 2002 it found 95, but last year the figure dropped to 67.
David Morrison of the NASA Ames Research Center in Moffett Field, California, believes the drop reflects 鈥渢he fact that we have already discovered nearly two-thirds of this population group.鈥� Astronomers estimate that there are probably about 1100 near-Earth asteroids and 691 have now been spotted. Morrison believes that at the current rate of discovery, Spaceguard should hit its target before 2010.
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Spaceguard is now turning its attention to smaller objects that could wreak regional devastation. Nearly 400 candidates smaller than 1 kilometre across were discovered last year.