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Since the moon is moving from the earth by few centimeters every year will it eventually fly away and if it does will make its own orbit around the sun and thus become a planet or will it fling it self into some other celestial object? Is this something that can be figured out?
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As I understand it, the moon will eventually stop receding and begin to come back towards Earth, never leaving its orbit, thusly never reaching even dwarf planetary status.
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"Where the telescope ends, the microscope begins. Which of the two has the greater view?" - Hugo "Men occasionally stumble over the truth, but most pick themselves up and hurry off as if nothing had happened." - Churchill |
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Increasing the scope of the criticism, Tau Ceti has an enormous debris disk which may subject inferior planets to impacts or at least regular, nightly light shows which would put our humble meteor showers to shame. Would those objects be defined as planets even if they're constantly bombarded? This definition isn't about to be changed any time soon AFAIK. Also I don't believe that the moon's just going to "fly away" like in Space 1999 and as phrased by gesturpa. It's going to reach a point where it is unable go any further and there aren't any significant perturbations to its orbit.
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A patriot must be ready to defend his country against his government - Edward Abbey, A Voice Crying in the Wilderness If only it was as easy to soothe my hunger by rubbing my belly. - Diogenes of Sinope |
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![]() Take that IAU! |
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Until our descendants figures out a way to eject the Moon. Maybe to use as a weapon against the Martian Confederacy.
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Fields of Space LOGIC, n. The art of thinking and reasoning in strict accordance with the limitations and incapacities of the human misunderstanding. In the Year 2525. "One small step for (a) man. One giant leap for mankind". If an astronaut doesn't need good grammar, niether does you. DDT, Removing invisible elves from backyards since 1939. |
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As for pluto and neptune, the resonance is why Neptune is considered dominant - it is in a stable, well established pattern in which Neptune is by far the gravitational superior.
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A patriot must be ready to defend his country against his government - Edward Abbey, A Voice Crying in the Wilderness If only it was as easy to soothe my hunger by rubbing my belly. - Diogenes of Sinope |
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Van Rijn's original Invisible Elf was running for the North Carolina Senate, but dropped out of the contest after the paparazzi snapped him with a cute pixie just outside Disney World in Florida. Now he has settled down with her as they await their first child, writing his biography of life in Van Rijn's backyard, - Now you prove me wrong |
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Numbers are not case sensitive. (me) |
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Van Rijn's original Invisible Elf was running for the North Carolina Senate, but dropped out of the contest after the paparazzi snapped him with a cute pixie just outside Disney World in Florida. Now he has settled down with her as they await their first child, writing his biography of life in Van Rijn's backyard, - Now you prove me wrong |
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I do so love fireworks!
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I am Mugs, of the Alien clan of Usa, Nordamerica, a Terran, of Sol. Perception isn't reality. It's merely an abstraction thereof, and quite often not a very good one at that. "Staying young requires the unceasing cultivation of the ability to unlearn old falsehoods." - Heinlein "Freedom begins when you tell Ms. Grundy to go fly a kite." - Heinlein |
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But it is the Moon's presence that keeps our axial tilt at the just so angle it is, otherwise life would be less comfortable, well so I am told
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Van Rijn's original Invisible Elf was running for the North Carolina Senate, but dropped out of the contest after the paparazzi snapped him with a cute pixie just outside Disney World in Florida. Now he has settled down with her as they await their first child, writing his biography of life in Van Rijn's backyard, - Now you prove me wrong |
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There actually have been suggestions by astronomers to label satellites of planets large enough to have achieved hydrostatic equilibrium as secondary planets (meaning they orbit planets instead of orbiting stars directly). |
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Actually, in the solar system, the distinction is quite clear (and we don't have any others to study in sufficient detail). There are no discovered objects that blur the boundary at all. Here is a plot of the mass ratios of some objects in our solar system (object mass vs other stuff in its orbital zone not gravitationally bound to it). See if you can find the obvious cutoff. There is actually far more ambiguity as to when an object has truly achieved hydrostatic equilibrium than there is in this.
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WANTED: Schroedinger's Cat Dead And Alive Last edited by cjl : 18-May-2008 at 12:06 AM. |
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OK. I created the graph myself, in microsoft excel. Now, to dig through my internet history for the source of the data...
OK, found it. The source is Steven Soter's paper "What is a Planet," submitted to the Astrophysical Journal (which is quite an interesting paper btw). Here is a link to it
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The further an object is from its parent star, the less likely it is to clear its orbit. This means if we find a Mars-sized object in the Kuiper Belt, according to the IAU definition, that object is not a planet while the real Mars is. There is an obvious problem here in that the definition looks solely at where the object is rather than what it is. Geophysically, Pluto and Eris are much more like planets than like asteroids. Yes, they are different from the other eight, but that simply means they fall under a different type or subcategory of planet. There is no ambiguity that these objects and Ceres have in fact achieved hydrostatic equilibrium. Astronomical definitions of other objects, such as stars and galaxies, cover a very broad range including many subcategories. Stars are not demoted because they are part of binary systems and therefore don't "clear their orbits." Tiny dwarf galaxies orbiting with the Milky Way are still considered galaxies even though the Milky Way could be said to control their orbits. Why should the definition of planet be so narrowly limited in a way that other astronomical definitions are not? |