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I End of the moon?

  1. Oct 31, 2016 #1
    Which scenario true about the Moon's end? Can someone explain me?
     
  2. jcsd
  3. Oct 31, 2016 #2

    berkeman

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    Welcome to the PF.

    You need to be a lot more specific and detailed in this question. What do you mean by "the end of the Moon"? Do you mean like if it gets hit by a big enough asteroid? Or when the Sun is near the end of its life and it eats the Moon and Earth? If you could post links to the reading you have been doing about this, that would help us to help you. :smile:
     
  4. Oct 31, 2016 #3
    Thank very much, sir.My English not good enough to explain myself but I will try.When Sun, becoming the Red Giant, it will probably swallow the earth, is that right? In this situation, what will happen to the Moon? Swallowed by Sun too? Or it will left to orbit long time ago? Or like you said, something crash to the moon and split that? Really, really sorry for my english and thanks your time!
     
  5. Oct 31, 2016 #4
    When the sun becomes a red giant in its last phases of life there are two possibilities for the Earth and moon:
    1. The Earth and moon will be consumed by the sun; or
    2. The Earth and moon will not be consumed.
    As the sun ages, particularly in its red giant phase, it also loses mass. As the sun loses mass it also loses its gravitational attraction on the planets and they begin to orbit further and further away from the sun. Therefore, by the time the sun reaches its red giant phase it might be possible for both the Earth and the moon to escape being destroyed by the sun. However, even if the Earth and moon escaped destruction by the sun, they both would be close enough to the sun's surface to be burnt to a cinder.



    Sources:
    Distant future of the Sun and Earth revisited - Oxford Journals, Monthly Notices of the Royal Astronomical Society, Volume 386, Issue 1 (arXiv free reprint)
    Orbital effects of Sun's mass loss and the Earth's fate - arXiv GR-QC/0511138
    The Sun Will Eventually Engulf Earth--Maybe - Scientific American, September 1, 2008
     
  6. Oct 31, 2016 #5
    Which is more possible scenario? What do you think?
     
  7. Oct 31, 2016 #6
    We do not have a good enough understanding of exactly how large the sun may become in its red giant phase, nor precisely how much the Earth's orbit may increase by. Therefore this question cannot be answered with confidence today. As our models of solar evolution improve we may well be able to do so.

    That said, I believe that at present it is thought more likely that the Earth will escape being swallowed. That view could change as we improve our understanding.
     
  8. Nov 2, 2016 #7

    Chronos

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    The moon currently receeds from earth by about 4 meters per century, according to lunar laser ranging data, due to tidal braking. This also slows down earth's rotation. By the time the moon receeds from its current average distance of about 400,000 km to 550, 000 km an earth day will nearly double and ocean tides [assuming any oceans remain] will cease. In theory, the moon would then reverse course and begin to creep back towards earth. If this continues long enough [and we are talking a very very long time] Also, in theory, the moon would eventually creep inside the earths Roche lobe and be destroyed by earth's gravity, forming pretty Saturn-like rings around earth. Of course, this assumes that in the mean time the sun does not consume the earth or moon and earth retains its oceans. So just how long might this take? To put it in perspective, the moons average orbital distance will increase about 10% and an earth day will increase around 3-4 hours over the next billion years - which is probably long enough for the oceans to be evaporated by the sun, thus eliminating the primary cause for the moon's orbital changes. So, gravitational destruction of the moon by earth is an unlikely fate for our moon. For discussion, see http://www.davidreneke.com/the-fate-of-our-moon/
     
    Last edited: Nov 2, 2016
  9. Nov 2, 2016 #8

    Bystander

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    Come again?
     
  10. Nov 2, 2016 #9

    Chronos

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    No oceans ~ no tides ~ no tidal braking.
     
  11. Nov 2, 2016 #10

    Bandersnatch

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    Crustal tides are still a thing. Every part of a body that is not an ideal rigid solid can produce a tidal bulge.
     
  12. Nov 2, 2016 #11

    Bystander

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  13. Nov 2, 2016 #12

    Bandersnatch

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  14. Nov 2, 2016 #13

    Bystander

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    "Solid" planet plus moon is only four per cent the braking of an earth sized (and shaped) liquid ocean.
     
  15. Nov 2, 2016 #14

    Bandersnatch

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    Yes, but that's a far cry from no braking.
     
  16. Nov 2, 2016 #15

    Bystander

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    One to one point five orders of magnitude is genuinely in "no man's land."
     
  17. Nov 3, 2016 #16

    Chronos

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    Im just saying tidal braking without oceans is a negligible factor, not zero.
     
  18. Nov 3, 2016 #17
    "...due to tidal braking."
    No argument there !!
    Wiki also mentions... " Most of the dissipation occurs in a turbulent bottom boundary layer in shallow seas such as the https://en.wikipedia.org/w/index.php?title=European_Shelf&action=edit&redlink=1 [Broken] around the British Isles, the Patagonian Shelf off Argentina, and the Bering Sea.[15]
    However, from the Topex/Poseidon data ... http://earthobservatory.nasa.gov/IOTD/view.php?id=654
    "... about 1 terawatt, or 25 to 30 percent of the total tidal energy dissipation, occurs in the deep ocean. The remainder occurs in shallow seas, such as on the Patagonian Shelf."
    IMHO, the deep ocean topography is *fairly* stable compared to the continental shelves, whose dissipation will be subject to ice ages, continental drift, the Wilson Cycle and such. For example, when Australasia, heading ~NE at ~62~70mm/yr closes the gaps around Indonesia, or when 'Sundaland' was dry during 'recent' ice ages...
     
    Last edited by a moderator: May 8, 2017
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