Chamberlin and Moulton"s hypothesis, the secondary nuclei in
them must revolve in a great variety of elliptic orbits
If the spiral nebulae have been formed in accordance with
Chamberlin and Moulton"s hypothesis, the secondary nuclei in
them must revolve in a great variety of elliptic orbits. The
orbits would intersect, and in the course of long ages the
separate masses would collide and combine and the number of
separate masses would constantly grow smaller. Moulton has
shown that IN GENERAL the combining of two masses whose orbits
intersect causes the combined mass to move in an orbit more
nearly circular than the average orbit of the separate masses,
and in general in orbit planes more nearly coincident with the
general plane of the system. Accordingly, the major planets
should move in orbits more nearly circular and more nearly in
the plane of the system than do the asteroids; and so they do.
If the asteroids should combine to form one planet the orbit of
this planet should be much less eccentric than the average of
all the present asteroid eccentricities, and the deviation of
its orbit plane should be less than the average deviation of
the present planes. We can not doubt that this would be the
case. Mercury and Mars, the smallest planets, should have,
according to this principle, the largest eccentricities and
orbital inclinations of any of the major planets. This is true
of the eccentricities, but Mars"s orbit plane, contrarily, has
a small inclination. Venus and the Earth, next in size, should
have the next largest inclinations and eccentricities, but they
do not; Venus"s eccentricity is the smallest of all. The
Earth"s orbital inclination and eccentricity are both small.
Jupiter and Saturn, Uranus and Neptune, should have the
smallest orbital inclinations; their average inclination is
about the same as for Venus and the Earth. They should likewise
have the smallest eccentricities. Neptune, the smallest of the
four, has an orbit nearly circular; Jupiter, Saturn and Uranus
have eccentricities more than 4 times those of Venus and the
Earth. Considering the four large planets as one group and the
four small planets as another group, we find that the
inclinations of the orbits of the two groups, per unit mass,
are about equal; but the average eccentricity of the orbits of
the large planets, per unit mass, is 21 times that of the
orbits of the small planets.[1] The evidence, except as to the
asteroids and Mercury, is not favorable to the planetesimal
hypothesis, unless we make special assumptions as to the
distribution of materials in the spiral nebulae.
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