The Moon: What is it's purpose?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by John99, Jan 23, 2009.

  1. Nasor Valued Senior Member

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    Things in space stay warm for a very long time, because there's nothing around to conduct the heat away. The only way to cool down is via black body radiation, which is very slow. When the space shuttle goes into space it has to immediately open its cargo bay doors to help radiate heat away, or it would rapidly get too hot.
     
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  3. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Partially, but mainly to show the aliens that we are friendly - inviting them in for tea, etc.

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  5. Roman Banned Banned

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    The moon doesn't have a purpose.
     
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  7. Nasor Valued Senior Member

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    Oh, don't worry, we're well past actually discussing the OP
     
  8. Saquist Banned Banned

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    A Mars sized Earth collision?
    are you serious? At what point? And why is this likely at all?

    Plus
    I'm very intrested in this "good explanation" you speak of. My head just instantly went back to the Theory of a temporary Earth Moon capture event.

    That was a good use of analogy.
     
  9. Nasor Valued Senior Member

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    I don't think I made an analogy. I was just trying to emphasize that things don't cool down quickly in space. The more surface area/volume you have, the faster you cool. Opening the shuttle cargo bay doors give a big increase in surface area. A spherical planet has the worst possible surface area/volume ratio, and will cool pretty slowly.
     
  10. Trippy ALEA IACTA EST Staff Member

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    Perfectly serious.
    I think about 3-3.5 billion years ago - don't quote that as an exact figure, i'm at work and too lazy to go and look it up. Among other evidence, I believe is the fact that around x-billion years ago the earths crust appears to have 'suddenly' thinned.

    Short answer - because the earths gravity (effectively) pulls the heavy elements closer to it, and the lighter elements float further away.

    Here's an analogy.

    Take a half pint of beer in a pint glass with a good head on it.
    Hold it out at arms length.
    The gravity of the earth pulls the beer down, and the froth floats on top of it.
    Think of the earths gravity as being the moons self gravity and the pint glass (and it's contents) as being a colum through the moons crust and mantle.
    Now we can all agree that when we spin something to create 'artificial gravity' that we're using 'centrifugal force' in lieu of gravity correct?
    So if, while holding your pint of beer at arms length, you start spinning around on the spot, you will 'generate' some 'centrifugal force' acting on the beer, which can be thought of as an artificial gravity. This 'artificial gravity' represents the earths gravity.
    If you look at your beer and the head, you will find that the beer tends to collect on on the outwards side of the pint glass, and the froth on the inside, but if your beer has enough of a head, then there's still froth over all the beer.
    So, if the outside of the pint glass is the near side of the colum, and the inside (from your perspective) is the far side of the colum, then we would expect the crust (or froth) to be thicker on the far side, then on the near side.
    Incidentally, this is how we know the lopsidedness has nothing to do with centrifugal force, because if it did, the thickness distribution would be reversed.
     
  11. Saquist Banned Banned

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    And what sort of series of events do you suppose would perturb a MARS sized planet to colide with the stable orbit Earth?....I'm mean that's a bit hard to imagine a larger object or that this Mars side object formed with in the solar system in an unstable orbit and finally crash into the earth.

    That's far more complicated.


    I kinda figured that explanation was coming.

    Here's an analogy.

    uh huh. I understand.
     
  12. John99 Banned Banned

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    If it were gone tomorrow did it serve a purpose? a function?
     
  13. D H Some other guy Valued Senior Member

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    That is the prevailing hypothesis. It explains a lot of things, such as why the Moon has a fairly low amount of iron, why the Earth and Moon have very similar isotopic ratios oxygen, evidence that the Moon was largely molten early in its history.

    Google "giant impact hypothesis" for more.

    It was 4.533 billion years ago (how the GIH proponents came up with such a precise number, I don't know). There is no evidence that the "earths crust appears to have 'suddenly' thinned" that I know of. One consequence of the giant impact hypothesis is that the impact pretty much wiped out any evidence of what the Earth looked like before the impact.
     
  14. Saquist Banned Banned

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    The problem I have with the Theory is that they are propposing that Earth recieved it's 24 hour day from the impact. They're also suggesting that the Earth's current path around the sun is the result circular though eccentric.

    Now how does Mercury have an more eccentry orbit than Earth but Earth was invovled in a massive shape altering colision with another planet?
    There must be Mars sized objects flying all over the place in this early Solar System. Venus gets hit with one, Earth, and apparently Mars to which has a similar day length as Earth.

    Where are all these "Mars" sized objects now? They can't all have had perfect collisions to have been absorbed into the Struck Planet.
     
    Last edited: Feb 4, 2009
  15. Trippy ALEA IACTA EST Staff Member

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    Not neccessarily.
    The early solar system was a crowded place, and all that's really required is an orbital resonance with one of the big planets (eg Jupiter).
    Also, the orbtis of the inner planets are inherently chaotic.
     
  16. Trippy ALEA IACTA EST Staff Member

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    The number comes about because the age of the moon, and the size of the impactor set strong constraints on when it occured, as for the other thing, i've seen references to it, but I don't remember where. i'll have to go digging (when I have more time).
     
  17. bones Registered Member

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    Without our moon, we wouldn't be here..

    Without the Moon, I believe that we would not be here. In the form that we are anyways.. Human. The Moon has a few huge impacts on our planet that allow us the ability to live here. To find life out there in far off space, you'd have to have a similar Earth - Moon system.. For humans anyways. I would think. Not just a planet in the habitable zone. The moon caused the Earth to have a slowed down spin, which in turn (no pun intended) Enabled the Earth to create, and have a stable journey around its star. The Moon also created plate tectonics, which you definitely need for life. Also, the Moon gives us our tides.. Which if life starts in the water, tides are good to have. Back in the day, shortly after the Moon would've hit Earth, the moon would've been extremely close to the earth.. Would’ve been HUGE in the sky.. With this closeness, the waves and tides at that time would've been massive! Massive enough to wash water all around this planet. Hundreds if not Thousands of feet high!! Filling up those pools for life to begin.
     
  18. Roman Banned Banned

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    No.
    Stuff would change, but that doesn't imply purpose.
     
  19. Saquist Banned Banned

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    I'd go for that if we had any idea of how many "eddies" eventually became massive objects. I don't think we do.

    I think Venus is the only other planet that obviously had a massive collision with a Massive object. The slow retrograde rotation of 224 days is an obvious massive impact clue. But the planet has almost no tilt to speak of, and it's the least eccentric orbit of all the planets.

    I think both of these points away from a large impact. If the odds of solar impact are as good as you say at this point no planet should a straight axis and a circular orbit. Yet Venus does. That along with no internal magnetic field to me implies that retro grade motion was created by formation. Two Planetary eddies that "colided" in a similar orbital pattern. I think perhaps even in the same or similar orbit. The colision calused a retro motion off the other and the two melded with a slower rotation but ultimately didn't . (

    Any massive impact should have caused a tilt in the axis or cause the speed of the form to accelerate or decerlated. Mercury is 36 million, Venus is 67 million, and Earth is 93 mission and Mars is 141 million. Those are divisions are close to 35 million kilos between orbits.

    I want to check orbital speed of Venus to Mercury and Venus to for anomolies otherwise I think this more logical for Venus.

    As far as the Moon and Earth are concerned...
    Earth's tilt is the only sign of massive impact which could just as easily be the product of perturbation by near collisions in side 1.5 million km from the planet's center.

    Earth's eccentricity is 0.016710219 , Venus' 0.00677323 Orbital inclination, Mars 0.093 315,eccentricity Jupiter's 0.04839266 Orbital inclination Saturn — Eccentricity: 0.055 723 219 ,Uranus' orbit is 0.0471, Neptune Eccentricity: 0.011214269, Mercury 0.2056), Pluto Eccentricity: 0.248 807 66


    Mars is the Inner planet that truely shows after formation eccentricity. It's orbit is 13 times more eccentric that Venus and the massive scar as well as the impact craters and the rogue moons while Earth is only 2 times more eccentric.
    Earth's orbit is only 2x as eccentric as Venus and nearly the same as Neptune. Pluto is 36 times more eccentric and Mercury is in the same neighbor hood as far as eccentricity goes.
     
  20. D H Some other guy Valued Senior Member

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    You have to go to great lengths to make an impact explain Venus' orientation. Where is the impactor? If it is now part of Venus, an impact does not explain Venus orientation. (Venus' orbit is pretty much on the ecliptic.) If it is not part of Venus, where is it? Fortunately, an impact is not needed to explain Venus wierd orientation. See the references in [post=2148290]post #27[/post].

    An impact does, however, explain a lot of Martian anomalies. See http://www.space.com/scienceastronomy/080625-mars-impact.html, for instance.

    No, they don't. The reason the giant impact hypothesis (GIH) is currently winning the day is because it is more consistent with observation than any other hypothesis. That doesn't mean the GIH is correct; the GIH does not explain everything and there are a number of pieces of evidence that appear to contradict the GIH.

    This paper proposes an answer to the question, "where did the Moon come from?". The answer: It formed at one of the two triangular Sun_Earth Lagrange points.

    Balbruno, E., Gott, J.R. III, "Where did the Moon Come From?", Astronomical Journal, 129:1724-1745 (2005).
     
  21. Trippy ALEA IACTA EST Staff Member

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    Actually, that paper assumes the GIH and examines where the impactor came from - in other words, it's not saying the Moon formed at L4/L5, it's suggesting that if a Mars sized object formed at one of these locations it would become perturbed enough to enter an orbit that would eventually lead to a collision that meets the requirements of that predicted by the GIH.

     
  22. Saquist Banned Banned

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    Really?

    Okay. One more time.

    Two "planets" form in very similar orbits with slightly different orbital velocities. Let us assume they are nearly exactly opposed to each other in Orbit. Over time 'falling' material aiming for the sun collects on both masses. They're still very fluid and both have a counter clock wise rotation. Years down the line they meet 'slowly' Because they are both counter clockwise they're rotation grinds to halt when they colide, they meld and cool.

    No ejecta or streams of debris to create a moon.
    The orbits were the same from the start and the collision only produces a 2 degree tilt in the new planet with very very little eccentricity.
    A further result is that the dynamos that had been given spin by early coalesing has also ground to a near halt. Thus the planets minmal magnetic field, with no pump in the center the magma is more solid less fluid and heat reaches the surface far slower, so no currents in the magma layer to break up the crust. Venus' release of heat happens in 2,000 year periods of build up in which the entire surface liquifies and sinks into the magma layer.

    If the mass was small and rapidly rotating then the collision would end with a very slow retrograde.

    So why is this a more difficult explanation?
     
  23. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I can believe that the moon formed at L4 or L5 and that it was perturbed away from those rather shallow gravitational wells but not that it was then captured by the Earth. That would require still a third body of considerable size.

    I thus accept the theory that the moon was blasted out of Earth by a large body impact. (Possibly ejecting Earth crust that was where the Pacific Ocean is now, but that is not easy to support.) Probably several other “moons” existed in the initial post impact years until thrown into the Earth or a larger new moon to make the current moon as only two mutually orbiting masses (Earth and Moon) are stable. From Roche’s limit arguments we know that the current moon did NOT form with the Earth from a gas cloud. Fact that the moon is much larger wrt the planet (Earth in this case) than any other moon also suggests that moons co-formed from the gas cloud normally are a much smaller fraction of the total mass. (I.e. even without the Roche limit proof, the moon is unlikely to have formed with the Earth, when the Earth did.)

    BTW I am not much impressed by some simulation that show Jupiter could prevent any planet from forming in the asteroid belt as that assumes Jupiter formed faster than a small dense "pre-asteroid" planet could. I.e. I have not given on up the now discredited earlier idea that the asteroids are the (not yet scattered away by Jupiter) residue of an exploded planet.

    That old POV explains why some are nearly pure iron/nickel (from the planet's core) and does not require making the assumption that Jupiter had formed before the much smaller planet could. It seems counter intuitive to me that Jupiter's huge mass of gases would collect into one planet* before a much smaller mass of heavier elements would assemble a planet that could later explode due to high content of radioactive core materials making a natural positive thermal coefficient fission reactor. (Like Chernobyl foolishly was.)

    -----------------
    *As they tried (as the gas compressed) they would self heat and slow the process. - Not much of a problem with smaller dense planet forming.
    Especially if one considers that heavy atoms, with the same energy of light atoms (same temperature) have much less momentum, so an iron on uranium atom collisions can "stick" much easier than H on H2** etc. I.e. it seems at least plausible that the "later to be asteroids" planet had core rich in high atomic number atoms and could make a thermal run-a-way fission years after forming. Does anyone know if the relative abundance of the Ni & Fe isotopes found in the metallic asteroids is at least consistent with the nickel and iron having been subjected to relatively slow neutron flux for many months (pre explosion) at least?

    **Especially since molecular H3 is unstable anyway!

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