US Naval Observatory ephemerides of the largest asteroids

Authors
Citation
Jl. Hilton, US Naval Observatory ephemerides of the largest asteroids, ASTRONOM J, 117(2), 1999, pp. 1077-1086
Citations number
35
Categorie Soggetti
Space Sciences
Journal title
ASTRONOMICAL JOURNAL
ISSN journal
00046256 → ACNP
Volume
117
Issue
2
Year of publication
1999
Pages
1077 - 1086
Database
ISI
SICI code
0004-6256(199902)117:2<1077:UNOEOT>2.0.ZU;2-7
Abstract
A new set of ephemerides for 15 of the largest asteroids has been produced for use in the Astronomical Almanac. The ephemerides cover the period from 1800 through 2100. The internal uncertainty in the mean longitude at epoch, 1997 December 18, ranges from 0".05 for 7 Iris through 0".22 for 65 Cybele , and the uncertainty in the mean motion varies from 0".02 per century for 4 Vesta to 0".14 per century for 511 Davida. This compares very favorably w ith the internal errors for the outer planets in recent Jet Propulsion Labo ratory planetary ephemerides. However, because the asteroids have relativel y little mass and are subject to perturbations by other asteroids, the actu al uncertainties in their mean motions are likely to be a few tenths of an arcsecond per century. As part of the improvement to the ephemerides, new m asses and densities were determined for 1 Ceres, 2 Pallas, and 4 Vesta, the three largest asteroids. These masses are as follows: Ceres = (4.39 +/- 0. 04) x 10(-10) M-circle dot, Pallas = (1.59 +/- 0.05) x 10(-10) M-circle dot , and Vesta = (1.69 +/- 0.11) x 10(-10) M-circle dot. The mass for Ceres is smaller than most previous determinations of its mass. This smaller mass i s a direct consequence of the increase in the mass determined for Pellas. T he densities found for these three asteroids are 2.00 +/- 0.03 g cm(-3) for Ceres, 4.2 +/- 0.3 gm cm(-3) for Pallas, and 4.3 +/- 0.3 g cm(-3) for Vest a. The density for Ceres is somewhat greater than that found for the taxono mically similar 253 Mathilde.