The Distribution of Asteroids in the Direction Perpendicular to the Ecliptic Plane

Extract

For examining the steady-state distribution of asteroids in the direction perpendicular to the ecliptic plane (the z distribution), we shall assume all orbits to be circular. This assumption is incompatible with the north-south asymmetry found by Nairn (1965); but Kresak (1967) has shown that the asymmetry is caused by a combination of cosmic and human factors and is present only among fainter asteroids, B(a, 0)> 16, where the discovery is grossly incomplete. There is another perhaps even more cogent reason for using only the brighter asteroids: The easily understandable practice of confining asteroid hunting close to the ecliptic plane has meant that among the fainter objects, orbits with high inclinations are underrepresented (Kiang, 1966). Actually, in the range 14<B(a, 0)< 15 where, I estimate, the discovery is 95 percent complete, the sample of inclinations may already be somewhat biased in the same sense. One has to balance this risk, however, with the advantage of a much greater data size; and I shall use all the numbered asteroids with B(a, 0)< 15 as given in the 1962 Ephemeris volume (excluding 13 that are regarded as “lost”).