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Uranus's axis
In article ,
Russell Wallace wrote: On Sun, 7 Sep 2003 08:46:53 -0700, "Chosp" wrote: Your question was, in fact, answered. You used the word pull in the present tense. Nothing has to continually pull it in a direction perpendicular to its orbit around the sun. How it originally got that way is not known for certain. There simply isn't enough information to completely rule out any one of a number of hypotheses. I suspect "how it originally got that way" was the intent of his question. That's something I'm curious about as well, though I don't have a clue about the answer - in particular, if an impact tipped the axis over (which is the one candidate explanation I know of), how would that have made its moons follow suit? Are there any hypotheses which would account for that? Well, at least that can easily be explained: the moons of Uranus were formed after the rotational axis of Uranus had been tipped. -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://www.stjarnhimlen.se/ http://home.tiscali.se/pausch/ |
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Uranus's axis
I suspect that even more people are disappointed when science CAN
explain something... :-) On Mon, 8 Sep 2003 06:28:10 +0000 (UTC), (Paul Schlyter) wrote: In article , Greg Neill wrote: "Bill" wrote in message ink.net... I apologize for using the word astrology instead of astronomy, however I was surprised that no one knew the answer and could only reply to my misuse of words. I was disappointed. Thanks anyway. ??? You received several answers. How is it you missed them? In one way he was right though: currently, science has no answer to why Uranus' rotation axis has such a large inclination. And some people who don't understand the scientific process but instead view science as a kind of religion get disappointed when learning about something science cannot explain. |
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Uranus's axis
In message , Paul Schlyter
writes In article , Russell Wallace wrote: I suspect "how it originally got that way" was the intent of his question. That's something I'm curious about as well, though I don't have a clue about the answer - in particular, if an impact tipped the axis over (which is the one candidate explanation I know of), how would that have made its moons follow suit? Are there any hypotheses which would account for that? Well, at least that can easily be explained: the moons of Uranus were formed after the rotational axis of Uranus had been tipped. Not necessarily. The original moons would probably have been ejected or destroyed during the impact, but if not, tidal forces would bring them into line with the equator. -- "Forty millions of miles it was from us, more than forty millions of miles of void" |
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Uranus's axis
On Mon, 8 Sep 2003 18:37:54 +0100, Jonathan Silverlight
wrote: Not necessarily. The original moons would probably have been ejected or destroyed during the impact How do you reckon? Wouldn't the impactor miss most or all of them? but if not, tidal forces would bring them into line with the equator. They would? Okay, fair enough. (Why doesn't this happen with e.g. Earth's moon, various bits of debris orbiting the Sun in inclined orbits, or globular clusters orbiting our galaxy in such orbits? Is it a case of they will eventually but the forces involved are relatively weaker so not enough time has elapsed yet?) -- "Sore wa himitsu desu." To reply by email, remove the small snack from address. http://www.esatclear.ie/~rwallace |
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Uranus's axis
"Russell Wallace" wrote in message
... On Mon, 8 Sep 2003 18:37:54 +0100, Jonathan Silverlight wrote: Not necessarily. The original moons would probably have been ejected or destroyed during the impact How do you reckon? Wouldn't the impactor miss most or all of them? but if not, tidal forces would bring them into line with the equator. They would? Okay, fair enough. (Why doesn't this happen with e.g. Earth's moon, various bits of debris orbiting the Sun in inclined orbits, or globular clusters orbiting our galaxy in such orbits? Is it a case of they will eventually but the forces involved are relatively weaker so not enough time has elapsed yet?) Earth's moon is rather large as far as moons go. There's a *lot* of angular momentum to deal with. The relaxation time would be very long indeed. |
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On Tue, 9 Sep 2003 09:43:34 -0400, "Greg Neill"
wrote: Earth's moon is rather large as far as moons go. There's a *lot* of angular momentum to deal with. The relaxation time would be very long indeed. So if our moon were the size of e.g. Phobos or Deimos, it would be orbiting over Earth's equator by now? How does that work? I would have though the gravitational force per kilogram on a moon didn't vary with the moon's mass? -- "Sore wa himitsu desu." To reply by email, remove the small snack from address. http://www.esatclear.ie/~rwallace |
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"Russell Wallace" wrote in message
... On Tue, 9 Sep 2003 09:43:34 -0400, "Greg Neill" wrote: Earth's moon is rather large as far as moons go. There's a *lot* of angular momentum to deal with. The relaxation time would be very long indeed. So if our moon were the size of e.g. Phobos or Deimos, it would be orbiting over Earth's equator by now? How does that work? I would have though the gravitational force per kilogram on a moon didn't vary with the moon's mass? It's a matter of torque and energy dissipation. In other words, inertia. Phobos and Deimos are mere specks of dirt compared with the Moon. So I'd say, yes, if they were in orbit about the Earth at a comparably close distance, then they would be tidally locked and orbiting very nearly in the plane of the equator by now. The Sun's influence would cause purturbations, of course, since the equator is tilted w.r.t. the ecliptic. |
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Uranus's axis
In article ,
Greg Neill wrote: "Russell Wallace" wrote in message ... On Tue, 9 Sep 2003 09:43:34 -0400, "Greg Neill" wrote: Earth's moon is rather large as far as moons go. There's a *lot* of angular momentum to deal with. The relaxation time would be very long indeed. So if our moon were the size of e.g. Phobos or Deimos, it would be orbiting over Earth's equator by now? How does that work? I would have though the gravitational force per kilogram on a moon didn't vary with the moon's mass? It's a matter of torque and energy dissipation. In other words, inertia. Phobos and Deimos are mere specks of dirt compared with the Moon. So I'd say, yes, if they were in orbit about the Earth at a comparably close distance, then they would be tidally locked and orbiting very nearly in the plane of the equator by now. Yes they would, but the reason would be the proximity to the Earth, not their small sizes. Phobos and Deimos may be tiny specks compared to the Moon, but they're huge giants compared to the artificial satellites we've launched. And our artificial satellites don't move towards an equatorial orbit much faster because of their very low mass.... The Sun's influence would cause purturbations, of course, since the equator is tilted w.r.t. the ecliptic. -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://www.stjarnhimlen.se/ http://home.tiscali.se/pausch/ |
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"Paul Schlyter" wrote in message
... In article , Greg Neill wrote: It's a matter of torque and energy dissipation. In other words, inertia. Phobos and Deimos are mere specks of dirt compared with the Moon. So I'd say, yes, if they were in orbit about the Earth at a comparably close distance, then they would be tidally locked and orbiting very nearly in the plane of the equator by now. Yes they would, but the reason would be the proximity to the Earth, not their small sizes. Phobos and Deimos may be tiny specks compared to the Moon, but they're huge giants compared to the artificial satellites we've launched. And our artificial satellites don't move towards an equatorial orbit much faster because of their very low mass.... Suppose we could perform two trials. In one we put, say, Phobos in a given proximate orbit to the Earth and timed its orbit's relaxation to an equitorial one, and then did the same with a small satellite (after removing Phobos, of course). Would we see the same relaxation time? What factors might influence the results? Certainly the smaller satellite would present less volume for tidal action (inverse cube with distance) and dissipation of energy in its structure. The satellite would also be much more rigid. The small satellite would not raise measurable tides on the Earth, but then tides due to Phobos would be tiny, too. The larger size of Phobos would present a slightly larger "handle" for torques, due to the tidal bulge of the Earth, to act. In computing the gravitational parameter mu for the system, the satellite's mass would be totally negligible, and Phobos' nearly so. But the mutual gravitational force would be ever so slightly larger and the orbital period ever so slightly shorter. Have I missed anything? |
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