Eight more moons for Saturn |
Eight more moons for Saturn |
Jul 15 2006, 07:32 PM
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#16
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Member Group: Members Posts: 509 Joined: 2-July 05 From: Calgary, Alberta Member No.: 426 |
Add various disturbances and it becomes clear that no large satellite can have own moons in our Solar System. It would be interesting, though, if some of these outer-irregular satellites of the giant planets were of the double-asteroid type, i.e. two similarly sized bodies in close orbit. Cassini might be able to resolve this sort of thing (albeit just barely). |
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Jul 15 2006, 08:35 PM
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#17
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Member Group: Members Posts: 249 Joined: 11-June 05 From: Finland (62°14′N 25°44′E) Member No.: 408 |
If the irregular satellites originate from captured and disrupted asteroids, it wouldn't be surprising if some of them are close (or contact) binaries.
Aren't they way too far to be detectable by Cassini? -------------------- The universe is not only stranger than we imagine, it is stranger than we can imagine.
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Jul 16 2006, 02:46 AM
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#18
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Member Group: Members Posts: 903 Joined: 30-January 05 Member No.: 162 |
Seems like Iapetus would have a uniquely large Hill sphere for a moon . . . .
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Aug 5 2006, 11:39 AM
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#19
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Newbie Group: Members Posts: 9 Joined: 5-August 06 From: Berlin (Milky Way) Member No.: 1014 |
Titan probably has larger Hill sphere than any other satellite. Still, the radius of its Hill sphere is mere 52,400 km. Callisto, whose orbital radius is larger, has slightly smaller Hill sphere (50,100 km). Jupiter's greater mass and smaller orbital distance makes Ganymede's Hill sphere much smaller, only 31,700 km in radius. Add various disturbances and it becomes clear that no large satellite can have own moons in our Solar System. Hi, using the Hill sphere formula given in this chat, it becomes indeed obvious that the larger satellites have Hill spheres about 1-2 orders of magnitudes smaller than the planets: Ganymede 0.00021 AU Callisto: 0.00033 AU Titan: 0.00035 AU Iapetus: 0.00025 AU Mercury, in comparison, has 0.0015 AU. However, tiny asteroid (243) Ida has only 0.00005 AU, or 8200 km, but owns a satellite. How does this work? T. |
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Aug 5 2006, 03:07 PM
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#20
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Member Group: Members Posts: 509 Joined: 2-July 05 From: Calgary, Alberta Member No.: 426 |
However, tiny asteroid (243) Ida has only 0.00005 AU, or 8200 km, but owns a satellite. How does this work? Simple... the satellite has to stay closer (in practice, substantially closer) than 8200 km from Ida. Otherwise the sun will snatch it away. Staying within the Hill sphere, though, is no guarantee of a stable orbit when we're talking about satellites of satellites. The Galilean satellites all have Hill spheres, but that doesn't mean they can have moons of their own. For example, anything going into orbit around Callisto (within Callisto's Hill sphere) would probably be able to stay in that orbit for a year or two. Eventually, though, the huge gravitational perturbations from Jupiter would destabilize it. It would most likely end up crashing into Callisto. This is one of the problems that has to be considered for the Europa Orbiter; it will need to constantly stabilize itself, and that's going to eat up fuel. |
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Aug 6 2006, 02:55 PM
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#21
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Member Group: Members Posts: 249 Joined: 11-June 05 From: Finland (62°14′N 25°44′E) Member No.: 408 |
Dactyl's orbit is poorly constrained, but it is roughly 100 km.
-------------------- The universe is not only stranger than we imagine, it is stranger than we can imagine.
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