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Showing results for tags 'tidal forces'.
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The forest frosts around you, but there's a spring in your step. The wood's getting colder by the hour, and already most of the region's larger wildlife has retreated to its dens. Or at least, so you hope; not many of Rimelight's nocturnal fauna have been catalogued yet. Stopping by the shores of an iced over lake, you set your gaze skywards. A mere glance upward justifies this world's name; the sky itself almost seems to have frosted over. Arcs of magnificent icy rings dominate the heavens, appearing in celestial increments around the enormous turquoise globe in the center of the cosmic firmament. Finding yourself beaming once again at the sight, you begin setting up your trusty telescope. There's a lot of ring-gazing to do before the sun rises in twenty more Earth-hours. This is the vague conception I have for a new science fiction worldbuilding project: I am attempting to design a planetary system in which a functioning multicellular ecology could evolve on a shepherd moon. I think I could do some pretty nifty things with the setting, but I need a little guidance on the proper astrometrics of such a system. A shepherd moon is a moon that orbits around the edge of a gas giant's ring system. They may also appear within gaps between the rings. A shepherd moon is defined by the gravitational effect it projects upon the ring particulates--it "herds" the dust and ice particles into sharp, stable shapes like those of Saturn's characteristic rings. Shepherd moons orbit close enough to the rings of their planet that I imagine the view from one would be spectacular; unfortunately, there are a few astronomical issues I'm facing in this world construction. First of all: the moon can't be located too close to the planet itself. The tidal forces of an object as large as a gas giant could literally destroy the moon every other week. If you don't believe me, check out the maps of Io--or the lack thereof. Jupiter's tidal forces, coupled with those of the nearby moons, is enough to bring the moon's magma to the surface and completely restructure the continents on a regular basis. It's hard to imagine carbon-based, water-filled life surviving in such an inhospitable habitat. That means that the moon of Rimenight will need to be an outer shepherd, orbiting far enough away from the planet that the tidal forces don't tear the crust apart like an almond flour pizza crust that's been in the oven too long. But if I position the moon too far away, it could take well over a week to orbit its parent body--thus radically lengthening the day/night cycle. Weeks of day followed by weeks of night could make for a fascinating setting itself, but it isn't at all what I want for Rimenight. I want a day/night cycle no longer than three Earth days. The proper distance from the gas giant would be bewildering enough for me to figure out--but since I want this to be a shepherd moon with a good view of the rings, I'll need to contend with the issue of the moon's "flock." Wikipedia cheerfully informs me that one of the primary mechanisms of a shepherd moon's herding is the accretion of rogue particles from the ring system. Now, "accretion" is just fine for a rocky potato like the ones that pick up rocks as they orbit Saturn, but for a world with a complex ecosystem, "accretion" looks more like this: I'm fine with a few extinction-level impact events on this world. As long as the major impacts are limited to once every thirty million years or so, I can play around with a fascinating Eocene-like ecosystem for this moon's bioregions. But my concern is that a shepherd moon, even one with a thick atmosphere, even one with other moons drawing away fire, would undergo such a massive and continuous pummeling that cellular life, much less multicellular life, might never get the chance the evolve. So in summary: I need to know the habitable zone for a moon orbiting a Saturn-sized gas giant. I also need to know how common and how severe impact events would be over this moon's history. If the answer to the previous question is "pretty sparking bad", then I'd appreciate some guidance on how to lessen the hostility of the environment. Thanks in advance! Anyone who posts comments on this thread gets a Rimenightian geologic feature named after him/her!
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