Estimates of Mass and Angular Momentum in the Oort Cloud

Abstract

Estimates can be made of unseen mass (in the form of cometary nuclei) at the heliocentric distances between 3 x 10(3) and 2 x 10(4) astronomical units(AU) under the assumptions (i) that the Oort cloud is a rarefied halo surrounding the core (dense, inner cometary cloud) and (ii) that the mass and albedo of comet Halley is typical for comets both in the core and the Oort cloud populations. The mass appears to be approximately 0.03 solar masses, with angular momentum of the order of 10(52) to 10(53) g-cm(2)/s. This mass is of the order of the total mass of the planetary system before the loss of volatiles. This leads to an estimate of a mass M(o) approximately 100 M( plus sign in circle) (where M( plus sign in circle) is the mass of Earth) concentrated in the Oort cloud (r > 2 x 10(4) AU) with an angular momentum that may exceed the present angular momentum of the whole planetary system by one order of magnitude. The present angular momentum of the Oort cloud appears to be of the same order as the total angular momentum of the planetary system before the loss of volatiles.

Observation of light echoes around very young stars

“…This mass is smaller than that in the minimum-mass solar nebula (Weidenschilling 1977), suggesting that the observed amount of dust around S CrA could have originated in its protoplanetary disk. Estimates of the mass of the current Oort cloud range from several to 100 Earth masses (Weissman 1983;Marochnik et al 1988), which is considerably lower than 2 × 10 −3 M , but one should keep in mind that the Oort cloud is not made of dust, but of larger bodies, as small grains are not expected to survive for billions of years due to non gravitational perturbations.…”

W Hya through the eye of Odin

“…This is considerably smaller than the estimated mass of water ice in the Solar System, assuming most of the present mass of water is bound in comets. The current estimate of the original mass of the Oort Cloud is highly uncertain and varies between 14-1000 M ⊕ (Bailey & Stagg 1988;Weissman 1991;Marochnik et al 1988). We speculate that icy bodies can be either part of the disk (and planets) left over after the formation of the central star, or a remnant envelope of the original cloud from which the star formed, reminiscent of the Oort Cloud.…”

Comets and Constraints on Solar System Formation

“…Since low velocities are required for the aggregation of the cometary material, it confirms an outer planetary region of formation. The mass of the Oort cloud is not well known because of uncertainties in the bulk density of cometary nuclei and in the nucleus size distribution ; recent estimates for the total cloud mass (outer cloud, inner cloud, Kuiper belt) range from 14 to 1000 Earth masses, with an original mass that could have been about a factor of 2 to 5 larger (Bailey and Stagg, 1988 ;Marochnik et al, 1988 ;Weissmann, 1985Weissmann, , 1991.…”