The Evolution of Worlds

by Percival Lowell

A fifth congruity is no less striking. All the satellites of all the planets that we can observe well enough to judge of turn the same face always to their lords. That the Moon does so to the Earth is a fact of everyday knowledge, and the telescope hints that the same respectful regard is paid by Jupiter’s and Saturn’s retinues to them. What is still more remarkable, Mercury and Venus turn out to observe the like vassal etiquette with reference to the Sun. And it will be noticed that they stand to him the nearest of his court. Here, then, is a law of proximity which points conclusively to some well-established force.

Last is a remarkable congruity which study disclosed to me likewise some years ago, and which has received corroboration in discoveries since. This congruity is the peculiar arrangement of the masses in the solar system.

Consider first the way in which the several planets, as respects size, stand ordered in distance from the sun. Nearest to him is Mercury, the smallest of all the principal ones. Venus and the Earth follow, each larger than the last; then comes Mars, of distinctly less bulk, and so to the asteroids, of almost none. After this the mass rises again to its maximum in Jupiter, and then subsequently falls through Saturn to Uranus and Neptune. Here we mark a more or less regular gradation between mass and position, a curve in which there are two ups and downs, the outer swell being much the larger, though the inner, too, is sufficiently pronounced.

Now turn to Saturn and his family, which is the most numerous of the secondary systems and that having the greatest span. Under Saturn’s wing, as it were, is the ring, itself a congeries of tiny satellites. Then comes Mimas, the smallest of the principal ones; then Enceladus, a little larger; then Tethys, the biggest of the three. Next stands Dione, smaller than Tethys. Then the mass increases with Rhea, reaching its culmination in Titan, after which it declines once more. Strangely reproductive this of the curve we marked in the arrangement of the planets themselves, even to the little inner rise and fall.

Masses of planets and satellites.

Striking as such analogous ordering is, it is not all. For, scanning the Jovian system, we find the main curve here again; Ganymede, the Jupiter or Titan of the system, standing in the same medial position as they. Lastly, taking up Uranus and his family of satellites, the same order is observable there. Titania, the largest, is posted in the centre.

Thus the order in which the little and the big are placed with reference to their controlling orb is the same in the solar system and in that of every one of its satellite families. Method here is unmistakable. Nor is it easy to explain unless the cause in all was like. That the rule in the placing of the planets should be faithfully observed by them in the ordering of their own domestic retinues, is not the least strange feature of the arrangement. It argues a common principle for both. Not less significant is the secondary hump in their distribution, denoting recrudescence farther in of the primary procedure shown without.

One point to be particularly noticed in these latter-day congruities is that they are not simply general concords like the older ones—the fact that the planets move in one plane or in the same sense in that plane—but detailed placings, ordered according to the distances of the planets from the Sun or of the satellites from the planets. They are thus not simply of the combinative but of the permutative order of probabilities, a much higher one; in other words, the chance that they can be due to chance is multiplicately small. Thus just as these analogies are by so much more remarkable, so are they by so much more cogent. They tell us not only of an evolution, but they speak of the very manner of its work. They do not simply generalize, they specify the mode of action. The difficulty is to understand their language. It is a case of celestial hieroglyphics to which we lack the key.