Art. XIII.—On the Causes tending to alter the Eccentricity of Planetary Orbits.—By Professor A. W. Bickerton.
[Read before the Philosophical Institute of Canterbury, 6th May, 1880.]
Plate I.
In former papers it has been shown that the partial impact of cosmical bodies may not unfrequently produce a central mass and attendant bodies, which I have called respectively a sun or nebula, and planets. The sun is at a high temperature and rotates. The planets, in a solid, liquid, or gaseous state, revolve round in one general plane with orbits of varying area and of high eccentricity. All the motions, whether of sun or planets, have one common direction. Further it was shown that the planetary path is due to a portion of the original proper motion escaping conversion into heat at impact. For the same reason the temperature of the planet is lower than that of the sun, whose high molecular velocity, due to its temperature and comparatively small mass, may cause it to expand into a nebula.
The present paper requires that the central mass shall become a nebula, and shall expand beyond aphelion distance of the most remote planet. The forces acting on the planet will be the attraction of the nebula, gaseous adhesion while traversing the nebula, and at the same time exchange of molecules with those of the nebula. The heavier molecules will generally be attracted to the planet, while the lighter ones will leave it. The probability of such a system being formed, or the possibility of gaseous planets moving in a nebula with its attendant effects on the size of the orbit and the change of apsides, is not treated in this paper. It is solely occupied with the change of eccentricity.
The following are five causes which are calculated to result in such a change:—
1st. An alteration in the amount of the attractive force exerted on the planet by the nebula.
2nd. The varying resistance and interchange of molecules incurred by the planet in its path.
3rd. The gaseous adhesion to the planet revolving on its axis within a nebula.
4th. The accretion of some of the vast number of small bodies which would exist in the nebula.
5th. Some others which are too dependent upon the special character of the impact to be discussed at present.
