Using comet light-curve asymmetries to predict comet returns

Abstract

THE gravitational attractions of the Sun and planets do not account completely for the orbital motions of short-period comets, which tend to return to perihelia with some delay or advance as compared with the gravitational solution. Debate over the physical cause of these 'nongravitational effects' has continued from the time they were discovered, in the early nineteenth century. Uncertainty over their origin has made prediction of these effects for any particular comet impossible. To clarify the roles of the radial and transverse components of the nongravitational force, and thus to arrive at an accurate picture with predictive power, we have used observational data on gas production rates from comets as a diagnostic of the force. The shapes of the production curves, based mostly on visual light curves, correlate very well with the nongravitational delays or advances of a number of comets, and we have used this correlation to predict a substantial advance of the recent perihelion passage of comet P/Brorsen–Metcalf, as verified by observations.