For a brief period in December 2004, the odds of Apophis hitting Earth were estimated at 1-in-37 but changed as more observations were recorded. The 1-in-45,000 figure will change yet again, and it's expected that Apophis will become less of a threat, not more, as time goes on, Tholen said.

Brian Marsden, who recently retired as director of the Minor Planet Center at the Smithsonian Astrophysical Observatory at Harvard University, but remains involved in its work, said the probabilities frequently change substantially with increased observations.

Apophis "won't be dangerous ... at least not for centuries to come, millennium to come," Marsden said.