The Inclination Distribution of the Kuiper Belt

Abstract

We develop a general method for determining the unbiased inclination distribution of the Kuiper belt using only the inclination and latitude of discovery of known Kuiper belt objects (KBOs). These two parameters are well determined for each discovered object, so we can use all 379 known KBOs (as of 2001 January 1)-without knowing the object's precise orbit, area, detection efficiency, or the latitudinal coverage of the survey that found the object-to determine the inclination distribution. We find that a natural analytic form for the inclination distribution is a sine of the inclination multiplied by a Gaussian. The inclination distribution of all KBOs is well fitted by sini multiplied by a sum of two Gaussians with widths 2.6d+.8-.2 and 15deg+/-1deg. For this inclination distribution, the Kuiper belt has an effective area of 8100+1500-1100 deg2 and a FWHM of 12.5deg+/-3.5deg in latitude. The inclination distribution of the different dynamical classes appear different. The Plutinos are well fit by sini mulitplied by a single Gaussian of width 10.2d+2.5-1.8, the classical KBOs cannot be fit to a single Gaussian but are well fit by sini multiplied by the sum of two Gaussians of widths 2.2d+.2-.6 and 17deg+/-3deg, and the scattered KBOs are poorly fit by sini multiplied by a single Gaussian of width 20deg+/-4deg. The poor fit of the scattered objects is possibly a result of limitations of the method in dealing with large eccentricities. The effective areas of the Plutinos, classical KBOs, and scattered KBOs are 9300+/-1800, 6100+/-2100, and 17000+/-3000 deg2, respectively. The FWHMs are 23deg+/-5deg, 6.8d+2.0-3.6, and 44deg+/-10deg, respectively. In all cases, the inclinations of the Kuiper belt objects appear larger than expected from dynamical simulations of possible perturbations.