46 KANSAS ACADEMY OF SCIENCE. 
WHERE DID MARS GET ITS MOONS? 
By E. MiuuEer, Lawrence, Kan. Read before the Academy December 31, 1896. 
Newton’s law of universal gravitation is exemplified in the movements of all 
the heavenly bodies, without exception. The illustration nearest to us is that of 
our solar system. Planets, asteroids, satellites, meteors, and meteoric swarms are 
controlled by it, and caniot escape from its power under any circumstances. It 
makes no difference whether the body moves in an elliptic, parabolic, or hyper- 
bolic orbit, or in the direction of a right line; in any case the law holds good. 
The body moving may have such a marvelous velocity as to break away from the 
attraction of other bodies; yet the law remains in operation. In multiple sys- 
tems of stars, some of whose orbits have been determined, and others whose. 
orbits are now being investigated, the law is found to be valid. It is fair, there- 
fore, to presume from analogy that the universe of matter is all subject to the 
law that celestial bodies everywhere act upon each other directly as their masses 
and inversely as the square of their distances. 
It is true that the motion of a body in space may be so great as to effectually 
prevent the operation of the law, in spite of the attracting force of any other 
body, or of a number of others, or of an indefinitely great number of them, 
among which the moving body is passing. No. 1830 Groombridge is an ex- 
ample of a star traversing the celestial spaces at a velocity such that in the 
course of a great number of years the star will escape from the confines of 
our stellar system, and be forever after lost to our sight. Somewhere, some 
time, in the far distant future, 1830 Groombridge will be compelled to slacken 
speed, and acknowledge the supremacy of the law of universal gravitation, 
and will then no longer ‘‘devour its way” at the rate of 230 miles per sec- 
ond ; in other words, it will become a captive star amenable to law, and obliged 
to travel in an orbit of some sort or other. Illustrations of the capture theory 
are to be found in our own solar system, especially in the case of comets that 
have entered the system from outer space, and also of those remains of disinte- 
grated comets— meteoric swarms. There are families of comets belonging to 
our system that became members of it through the powerful influence of the 
giant planets. In every case of a comet of short period of revolution its orbit is 
found to be at certain points very close to the orbit of Jupiter, and when the 
comet’s path crosses that of Jupiter, as Professor Young says, ‘‘ one of the nodes 
is always near the place of apparent intersection, and if Jupiter were at that 
point on its orbit at the time when the comet was passing, the two bodies would 
really be very near each other. The fact as we shall see is a very significant one, 
pointing to a connection between these erratic bodies and the planet. This is 
true of all comets whose periods are less than eight years.’’ Some one has re- 
cently suggested that the fifth moon of Jupiter is the result of the capture of a 
comet by the planet. Is it not possible that some of the moons of the giant 
planets may have been comets taken on the wing, so to speak, and subsequently 
transformed into satellites? 
May not the movements of large comets passing through our system, hundreds 
of thousands of years ago, account for the backward revolution of the satellites 
of Uranus and Neptune? In the satellite system of Uranus, which apparently 
contradicts the theory of the nebular hypothesis, the plane of the orbits of the 
moons is inclined at an angle of 89°.2 to the plane of the ecliptic. We know 
that the inclinations of the orbits of the comets range all the way from 0° to 90°. 
