Note: to see the current impact probability for a specific asteroid, please visit our Risk page.

The calculation of impact probability involves the disciplines of orbital dynamics, estimation theory, and numerical analysis. The orbit of a comet or asteroid is determined from a set of observations (right ascension/declination coordinates). The observations are typically accurate to 0.5 arc-sec, although this can vary somewhat according to the pixel size used in the CCD detectors: some observatories have only 1.0 arc-sec accuracy. Because there are some errors in the observations, there will be uncertainties in the orbital determination for the object. The uncertainty in the orbital elements also depends on the number of observations and the time span over which they are made. The more observations we have, and the longer the time span, the less the uncertainties will be, and the more precise the orbit will become. Thus, for a newly discovered object, the uncertainties tend to be large initially. As more observations are obtained on the object's position, the uncertainties are reduced, and any potential impacts are then eventually eliminated for the vast majority of the cases. See also this animation, courtesy of the Spaceguard Foundation in Italy.