Comparison of original orbits of Oort Cloud new comets given in various
catalogues
Abstract
Nearly isotropic comets with very long orbital period are supposed to
come from the Oort Cloud. Recent observational and theoretical studies
have greatly revealed the dynamical nature of this cloud and its
evolutionary history. However, many issues are yet to be known. Our goal
is to understand current structure of this cloud as well as its
dynamical origin. For estimating the current structure of the Oort
Cloud, key information lies in the original orbit of the Oort Cloud new
comets (OCNCs) that are defined at a distance where these objects do not
receive gravitational perturbation from major planets (such as at rg =
250 au from the Sun before comets enter into the planetary region).
There have been several attempts to obtain OCNC’s original orbits, but
it never has been an easy task. This requires numerical orbit
propagation of the observed comets with high accuracy including
perturbation from major disturbing bodies. In addition,
non-gravitational forces often play significant roles here. First and
foremost, the orbit determination of OCNC includes substantially large
uncertainty because of limited number of observational arcs and very
large eccentricity of the comets (~1). Here we show our
preliminary result of comparison of various catalogues of OCNCs’
original orbital elements at rg = 250 au: So-called the Warsaw
catalogues by Krolikowska, the ephemeris given by MPC (Minor Planet
Center), that given by Horizons/JPL, and others calculated by a few
individuals (Marsden, Kinoshita, and Nakano). The resulting orbits that
these catalogues yield are overall similar, but sometimes they are
starkly different by reasons yet to be known. Through a series of plots
with a help of our own orbit propagation using numerical and analytic
methods, we give considerations on which catalogue yields the
information that is the most significant (or the most fundamental) for
understanding structure, origin, and evolution of the Oort Cloud.