How did the Earth capture the Moon ?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by river, Apr 26, 2020.

  1. river

    Messages:
    14,523
    To Issac Asimov it is simply not possible .

    The Earth simply does not have the mass to capture the moon .

    So why is the Moon orbiting the Earth ? ( and the moon does not rotate around its own axis ) . Hence why we see only one side of the Moon's surface , All the time . We never see the Dark Side of the moon , ever .
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. Halc Registered Senior Member

    Messages:
    226
    Current theories say it is not captured, but is rather a collection of ejecta from Earth, explaining its similar composition.

    Moon is orbiting Earth because it lacks energy needed to escape.
    The moon does rotate about its own axis each 27.3 days or so.
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. foghorn Registered Senior Member

    Messages:
    389
    https://www.space.com/24871-does-the-moon-rotate.html
    River, google ''Barycenter of the Earth Moon system.''
    The Earth and Moon are 'orbiting' the centre of mass of the Earth Moon system.
     
    Last edited: Apr 26, 2020
    sculptor likes this.
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. river

    Messages:
    14,523
    What Ejecta from Earth ?

    To your last statement , then why is the Dark Side of the Moon never shown to any point on Earth ?
     
  8. river

    Messages:
    14,523
    I get that , but the moon is not rotating , and the Barycenter of the Earth and Moon does not have the mass to contain the Moons original momentum away from us .
     
  9. river

    Messages:
    14,523
    Relative to the mass of the Earth , compared to other planets that have moons , they have enormous mass relative to the moons themselves .

    The Barycenter of other planets and their moons , systems , makes more sense than does the Barycenter of the Earth - Moon system .
     
    Last edited: Apr 26, 2020
  10. foghorn Registered Senior Member

    Messages:
    389
    I remember Asimov using the expression ''Double Planet'' to describe the Earth Moon system.
    https://www.goodreads.com/book/show/2681424-the-double-planet
     
    paddoboy likes this.
  11. river

    Messages:
    14,523
  12. foghorn Registered Senior Member

    Messages:
    389
    The Moon rotates on its own axis. It also orbits the center of mass of Earth Moon system.
     
  13. Halc Registered Senior Member

    Messages:
    226
    Get big hammer, go splat. Much bigger than the one that wiped out the dinosaurs.

    There is no dark side of the moon. Sun rises and sets every ~708 hours (about 29.5 days).

    Barycenter has nothing to do with the moon's rotation. A moon could in theory orbit Earth (revolve about it) without having any rotation. It would then have a day the same length as its year, but the stars in the distance would remain fixed from any given location. Hubble telescope moves in this manner.

    You speak of the moon's 'original momentum' away from us. The moon is hypothesized to be a collection of multiple objects (said ejecta). The fast ones never came back, the slow ones fell to Earth, and the ones between coalesced into the one object that is today's moon, which gains total energy but loses momentum (relative to Earth) over time. The original momentum might have been 30% (just a guess) higher than today. Momentum of an orbiting object has to do with its proximity to the thing orbited, so the moon, being closer back then, would move faster. As it gains energy, it moves further away and slows.
     
    Last edited: Apr 26, 2020
  14. (Q) Encephaloid Martini Valued Senior Member

    Messages:
    20,438
    If the moon didn't rotate on its axis, we would see all sides of the moon. Simple experiment, two people standing face to face several feet apart, one person starts to go around the other person while maintaining face to face. Notice that the person moving around rotates as they move.
     
  15. river

    Messages:
    14,523
    There is a Dark Side of the Moon , because we can never see it . Hence satellites that take photos of the dark side of the moon .

    The moon does NOT rotate .
     
  16. river

    Messages:
    14,523

    Highlighted

    Think about what you said here . Over and over .
     
  17. billvon Valued Senior Member

    Messages:
    18,326
    The Moon rotates about once a month. There is no "dark side of the Moon" contrary to popular opinion; the Sun rises and sets on the Moon every 29 days or so. Since it rotates as fast as it orbits, the same side faces us all the time.
    What was the Moon's original momentum?
     
  18. foghorn Registered Senior Member

    Messages:
    389
    https://svs.gsfc.nasa.gov/4709
     
  19. river

    Messages:
    14,523
    Ah ... so the Dark Side of the moon does face us , its just there is no light making it visible .
     
  20. river

    Messages:
    14,523
    Don't know . Nobody does .

    The moon rocks are , from radiometric dating , 4.44 billion yrs. old . Where as the oldest rocks from Earth are between , 3.8 to 4.28 billion yrs old .

    Thats 0.16 or 160,000 million yrs. older . ( 4.4 minus 4.28 , times a billion ) .

    Why ?
     
    Last edited: Apr 26, 2020
  21. river

    Messages:
    14,523
    Who can calculate how slow the Moon would have to go to have been captured by Earth ?

    Seriously .

    Because once we do that , then maybe we can figure out where in the solar system the Moon came from .
     
  22. psikeyhackr Live Long and Suffer Valued Senior Member

    Messages:
    1,136
    Further speculations on the origin of the Moon
     
  23. (Q) Encephaloid Martini Valued Senior Member

    Messages:
    20,438
    If and when you do actually figure this out, you'll think back to this post and realize how much of a fool you were for saying that.

    "The moon orbits the Earth once every 27.322 days. It also takes approximately 27 days for the moon to rotate once on its axis. As a result, the moon does not seem to be spinning but appears to observers from Earth to be keeping almost perfectly still. Scientists call this synchronous rotation."

    https://www.space.com/24871-does-the-moon-rotate.html
     

Share This Page