The Evolution of Worlds/Notes 4

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On the Planets' Orbital Tilts

The tilts of the plane of rotation of the Sun and of the orbits of the several planets to the dynamical plane of the system tabulated are:—

Mercury 6° 14′
Venus 2° 4′
Earth 1° 41′
Mars 1° 38′

Asteroids various
Jupiter 20′
Saturn 56′
Uranus 1° 2′
Neptune 43′

where, in the determination of that plane, the latest values of the masses of the planets and the rotations of the Sun, Jupiter, and Saturn have been taken into account.

These tilts suggest something, doubtless, but it is by no means clear what it is they suggest. They are just as compatible with a giving off from a slowly condensing nebula as with an origin by shock. The greater inclinations of Mercury and Venus may be due to their late birth from the central mass without the necessity of a cataclysm, the rotation of that central mass out of the general plane being caused by the consensus of the motions of the particles from which it was formed. The accordance of the larger planetary masses with the dynamical plane of the system would necessarily result from their great aggregations. So that this, too, is quite possible without shock.