{ "export": { "source": "https://urth.darkrealm.vip/thread/whorl/802", "note": "Exported from an unofficial mirror of a public mailing list. Copyright in each message remains with the person who wrote it. Email addresses are obscured as `user at host`, the form the original archive published. This file was rebuilt from parsed fields rather than retained headers, so it is faithful in content but not byte-exact.", "addresses": "obscured as 'user at host'" }, "archive": "whorl", "thread": { "id": 802, "subject": "Freaky Orbits", "messages": 2, "voices": 2, "first": "2000-04-03T15:54:46+00:00", "last": "2000-04-04T12:10:36+00:00" }, "messages": [ { "message_id": "", "from": { "name": "Michael Andre-Driussi", "address": "mantis at sirius.com" }, "date": "2000-04-03T15:54:46+00:00", "subject": "(whorl) Freaky Orbits", "in_reply_to": null, "reply_link": null, "blocks": [ { "kind": "text", "depth": 0, "text": "Adam Stephanides and Kieran Mullen,\n\nI am interested in your notes--of course you know I've been puzzling over\nthe orbital details, too.\n\nLately I've been thinking along the lines of those freaky orbits of\nSaturn's moons Janus and Epithemis (sparked into posting this by the refs\nto shepherd moons). Took me a few minutes just now, but I found a clean\nand easy reference:\n\n'Co-orbiting satellites are another weird example of a resonance. Saturn's\ntiny moons Janus and Epithemis nearly share an orbit; but one never passes\nthe other. They're forever going faster and slower in the orbit,\napproaching as though to pass a baton in a relay, only to drop back before\ngetting close enough to touch. As seen from Saturn, they'd get closer,\nslow down, and then separate again as though they'd \"bounced off\" each\nother. Things would look even more bizarre from one of the moons\nthemselves; you'd see the other moon approaching, but you'd slow down and\nit would speed up as you got closer, until finally it would flee out of\nsight. Then the whole pattern would repeat half an orbit later--but you'd\nhave to go around to the other side of the satellite to watch it again.'\n\n'The interaction is like that between a ring and a shepherd . . . '\n\n'The co-orbiters in Saturn's system are stable, and perhaps co-orbiting\nplanets occur somewhere, though I don't know that anyone's looked at the\ndynamics. Two Earthlike worlds, forever chasing each other around a star,\nis not a setting anyone's used, so far as I know!' (Gillett,\nWORLD-BUILDING, p. 34).\n\nSo I think we have a third model to consider.\n\nModel 1: Two Planets (Earth and Venus), with standard Bode-Titus style\norbits and a comparatively wide separation (significant fraction of an\nAstronomical Unit). (Problems: to see one as a looming disk from the\nsurface of the other, the world has to be much closer than this suggests.\nPossible solution: ditch Bode-Titus! )\n\nModel 2: Double Planet (Sainte Anne/Sainte Croix; Urth/Lune) quite close,\ncelestially speaking (which makes it hard to work in that \"six year\" bit),\norbiting around a common center between them (as well as going around the\nprimary star).\n\nModel 3: Co-orbiting Planets. Freaky orbit.\n\nGranted, there are immediate problems: if the model is exactly like that of\nSaturn's moons, then it couldn't be once every \"six local years,\" it would\nhave to be \"twice every local year.\" (Where local year = orbit.)\n\nThe Double Planet mode would work if you can have a wildly eliptic orbit,\nsuch that the two bodies get close every six local years--I haven't thought\nabout this particular angle long enough to form an opinion up or down!\n(Every six years! Holy cow, that's like a comet or something! Or maybe\nthe freaky orbits of Pluto and Neptune--whoops, there's a fourth\nmodel--where sometimes Pluto, the \"furthest planet from Sol,\" is sometimes\ninside the orbit of Neptune.)\n\n(Doh! Adam already mentioned something about the wildly eliptic orbit for\nDouble Planet approach.)\n\nModel 4: Crossing Orbits (like Pluto and Neptune). Only slightly less\nFreaky. (Mercury's got a Freaky Thang, too, but not germane to my rambling\nhere.) But making the Crossing Point a Close Encounter every six years,\nhwoof! That's nigh impossible, even with short \"inner world\" orbits.\nScratch this model in favor of number 3.\n\nAnyway, just throwing out some wild thoughts. Keep working, guys; I'm\nreading your notes and enjoying it. Just a little dizzy right now, I'll\ntry to stablize and contribute more asap.\n\n=mantis=\n\n\n\n*This is WHORL, for discussion of Gene Wolfe's Book of the Long Sun." } ] }, { "message_id": "", "from": { "name": "Jim Henley", "address": "jhenley at nas-corp.com" }, "date": "2000-04-04T12:10:36+00:00", "subject": "RE: (whorl) Freaky Orbits", "in_reply_to": "", "reply_link": "subject", "blocks": [ { "kind": "quote", "depth": 1, "text": "-----Original Message-----\nFrom: Michael Andre-Driussi [mailto:mantis at sirius.com]\nSent: Monday, April 03, 2000 6:55 PM\n\nAnyway, just throwing out some wild thoughts. Keep working, guys; I'm\nreading your notes and enjoying it. Just a little dizzy \nright now, I'll try to stablize and contribute more asap." }, { "kind": "text", "depth": 0, "text": "What if the orbits are not in the same plane?\n\nBest,\n\n\nJim\n\n\n*This is WHORL, for discussion of Gene Wolfe's Book of the Long Sun." } ] } ] }