Assortments of Thought

Other than all the stars, the Moon and the planets classically held attention and commanded wonder, whenever a civilization gazed into the heavens. Of course this was largely because so little was known of outer space, about what else was up there besides what could clearly be seen, but it shouldn’t be denied that the planets of our own solar system are indeed magnificent. And now, while we unfortunately have to rely as yet on artists’ conceptions to visualize them, the recent multitudes of exoplanets found have, along with theoretical considerations, yielded even more diverse and wondrous planets to inspire us. Yet moons and rings are presumably integral parts of planetary systems as well, and while moons at least are virtually certain to exist alongside and beyond many of the planets of our galaxy’s systems, their small sizes have presumably kept them invisible as yet to our instruments and detection methods. Even so, we might hazard that “large” planets nearly always have moons and rings, while “small” ones have them much less so; that most moons are “very small”, except that “large” planets typically have a few “larger” but still non-gaseous ones; that extensive rings are less common, and only ever exist around “large” planets; that most moons lack atmospheres, yet a fair number of systems have at least one atmospheric moon; and that non-unitary planets and moons are comparatively rare, as are moons or rings of moons. To see why these conjectures might be true, let us consider what, in terms of moons, rings, and non-unitary bodies, planetary systems in our galaxy and across all the cosmos might be like.

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