Quote:
Originally Posted by Fred Brackin
The Galilean moons of Jupiter have much the same problem as Earth's Moon. They obviously came from somewhere else and being small should be geologically old, all other things being equal. All planetary moons would probably have to be captured in this theory.
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I don't think that that necessarily follows. The original nebula largely collapses into a central mass (the sun) and a bunch of smaller masses (the planets); the planets could in turn collapse into a central mass and a bunch of smaller masses (the satellites). The satellites would then cool and solidify much faster than the planets, just as the planets cool and solidify faster than the sun. So you could have the Jovian and Saturnian satellite be solid and compact while the planets were still fluid and diffuse.
I agree that that wouldn't work for a satellite as large relative to the planet as the moon is. And Phobos and Deimos and the minor Jovian and Saturnian moons could be captured sky junk. But Titan and the Galilean satellites don't seem impossible to account for as tertiary condensations.
It's all a rather elegant model and could be fun in a steampunk setting.
By the way, one of the Doctor Doolittle books has the good doctor and his kid sidekick Thomas Stubbins visiting the moon and learning that its near-immortal inhabitants vividly remember when it broke away from the Earth, leaving the Pacific basin behind. . . .
Bill Stoddard