A study of the original orbits of “hyperbolic” comets

The problem of hyperbolic incoming orbits for single-apparition comets is investigated. In this context the effect of non-gravitational acceleration on cometary dynamics was analyzed for the sample of 33 “hyperbolic” comets. The orbital elements of each cometary orbit were determined by the least squares procedure based on positional observations. These osculating orbital elements serve as a basis for the determination of the incoming orbits. The new method of estimating the uncertainties of (1/a)ori based on a statistical approach to the orbit determinations is applied. For sixteen comets it was possible to determine the non-gravitational effects and original “non-gravitational” orbits. We show that for almost all the comets with detectable non-gravitational effects the incoming barycentric orbits changed from hyperbolic to elliptical when the non-gravitational effects were included. However, it was also ascertained that excess velocity at great distance are not cancelled by the nongravitational acceleration itself. We show that the non-gravitational effects are responsible for small modifications of the osculating elements (mainly eccentricity), which are sufficient, however, to obtain the elliptic original orbits for comets recognized in the literature as hyperbolic.