Abstract
A COMMON feature of the older theories of the origin of the solar system is that they all suppose it to have been derived from a more or less symmetrical rotating nebula in a gaseous or quasi-gaseous state. By some process, the details of which differ in different theories, this mass is supposed to have condensed locally to form the sun and planets. A recent paper by Jeans has indicated a way of examining whether such condensation is possible. Viscosity is insufficient to cause a mass so large as the primitive nebula to rotate like a rigid body; each part would revolve practically independently around the centre under gravity, and the matter near any point, on account of the differences between the velocities of different parts, would be in a state of rotation with an angular velocity different from that of its revolution as a whole. It is, however, easily shown that the two are of the same order of magnitude. Now a mass cannot condense locally unless the density is so great that mutual gravitation is enough to balance the centrifugal force due to the rotation, and this indicates that, before condensation started at distance r from the centre, the density there must have been at least comparable with the mean density of a sphere of radius r and mass equal to that of the sun. Planets having been formed at many different distances from the sun, it follows that the mass must have originally been widely distributed through the system. The distribution of density and velocity being thus fcnown within sufficiently narrow limits, it can be shown by the principle of the constancy of angular momentum that if planets of the sizes of ours were formed, the resulting central body could not possibly rotate so slowly as the actual sun. There is no agency capable of reducing this rotation, and it seems necessary to abandon completely those hypotheses that require the solar system to have been formed by the gradual condensation of a nebula.
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REFERENCES
J. H. Jeans : "The Part Played by Rotation in Cosmic Evolution," Monthly Notices of Royal Astronomical Society, vol. lxxvii., 1917, pp. 186–99; "Note on the Action of Viscosity in Gaseous and Nebular Masses," loc. cit., pp. 200–4; "The Motion of Tidally Distorted Masses, with Special Reference to Theories of Cosmogony," Memoirs of R.A.S., vol. lxii., 1917, PP. 1–48.
Harold Jeffreys : "The Resonance Theory of the Origin of the Moon," Monthly Notices, vol. lxxviii., 1917, pp. 116–31; "On the Early History of the Solar System," loc. cit., pp. 424–41.
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JEFFREYS, H. The Early History of the Solar System . Nature 101, 447–449 (1918). https://doi.org/10.1038/101447a0
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DOI: https://doi.org/10.1038/101447a0