The Intrinsic Distribution and Selection Bias of Long-Period Cometary Orbits

Abstract

A question that arises in the study of cometary orbits is whether or not the directed normals to the orbits are uniformly distributed on the celestial sphere. Previous studies by statisticians have not taken selection effects into account and have tended to reject uniformity. Here a plausible selection mechanism is proposed that gives rise to a one-parameter family of distributions on the sphere. Data on long-period comets are analyzed using this one-parameter family. A nonzero selection effect is detected, and its size is estimated. Subject to this selection effect, uniformity of the directed normals can no longer be ruled out.