Estimates of Mass and Angular Momentum in the Oort Cloud

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Science  28 Oct 1988:
Vol. 242, Issue 4878, pp. 547-550
DOI: 10.1126/science.242.4878.547


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.