Abstract
CAPTURE OF COMETS BY PLANETS.—During the last two or three years several astronomers have studied the action of planets in changing the orbits of comets which pass near them, and a considerable amount of interest has been aroused in this problem. Prof. H. A. Newton, in the American Journal of Science for September and December, establishes a number of propositions relative to the perturbations by planets which lead to the annexation of comets. Some of the results obtained may be expressed as follows.;—(1) If a comet passes in front of Jupiter, the kinetic energy of the comet is diminished; if it passes behind the planet, the kinetic energy of the comet is increased. (2) The greatest effect of perturbation of a planet moving in a circular orbit in shortening the periodic time of a comet originally moving in a parabola is obtained if the comet's original orbit actually intersects the planet's orbit at an angle of 45°, and if the comet is due first at the point of intersection, at the instant when the planet's distance therefrom is equal to the planet's distance from the sun multiplied by the ratio of the mass of the planet to the mass of the sun. (3) If in a given period of time 1,000,000,000 comets come in parabolic orbits nearer to the sun than Jupiter, 126 of them will have their orbits changed into ellipses with periodic times less than one-half that of Jupiter; 839 of them will have their orbits changed into ellipses with periodic times less than that of Jupiter; 1701 of them will have their orbits changed into ellipses with periodic times less than one and a half times that of Jupiter; and 2670 of them will have their orbits changed into ellipses with periodic times less than twice that of Jupiter. (4) Of the 839 comets which are reduced to have periodic times less than Jupiter's period, 203 will, after perturbation, have retrograde motions, and 639 will have direct motions. (5) Somewhat more than five times as many of these comets move in direct orbits inclined less than 30° to Jupiter's orbit as move in retrograde orbits inclined less than 30° to Jupiter's orbit. It may therefore be said that comets which are changed by the perturbing action of a planet from parabolic orbits of every possible inclination to the ecliptic into short period ellipses must, as a rule, move in orbits of moderate inclination, and with direct motions.
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Our Astronimical Column. Nature 45, 186 (1891). https://doi.org/10.1038/045186a0
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DOI: https://doi.org/10.1038/045186a0