L. M. Mukhin

Estimates of Mass and Angular Momentum in the Oort Cloud

Estimates can be made of unseen mass (in the form of cometary nuclei) at the heliocentric distances between 3 x 103 and 2 x 104 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 1052 to 1053 g-cm2/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 Mo ≃ 100 M⊕ (where M⊕ is the mass of Earth) concentrated in the Oort cloud (r > 2 x 104 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.

Evolution of the Oort cloud angular momentum: Numerical simulation

This paper considers the evolution of a flat svarm of cometary bodies (under the effect of the passage of stars), initially moving in one direction along the circular orbits with radii 1.4×104<r<2×104 AU and along elliptic orbits with semi-major axes 5×103<a<1×104 AU and with perihelia within 50<q<100 AU. Numerical simulation shows that the original flat belt of comets is thermalizing. Its root-mean-squarez-coordinate grows withr. A cometary cloud forms with a dense flattened inner core and a rarefied halo (the Oort cloud proper). The value β=Ncore/Nhalo varies within a wide range (up to the order of magnitude) depending on the model used (Ncore andNhalo are the numbers of comets in the core and the halo, respectively).The hypothesis of a massive Oort cloud (Marochniket al., 1988) implies that the Oort cloud should have a large angular momentum. This paper employs numerical simulation to calculate Oort cloud models to which the initially flat located at the periphery of the solar nebula rotating cometary swarms is evolving in time. The loss of the initial angular momentum over the time of the Oort cloud evolution is not large.