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What if the moon

  1. Oct 12, 2007 #1
    ...was destroyed by an asteroid which was destined for Earth? Where would that leave Earth? What would happen to Earth orbit? Rotation?
  2. jcsd
  3. Oct 17, 2007 #2
    If that happen,the rotation of the earth will faster !due to the angular momentum of the lunar system transfer to the earth !
  4. Oct 17, 2007 #3
    Earth would be hit by chunks of the moon leaving it full or craters and depending on the size of the chunks of the moon and parts of the asteroid that hit the moon that hit the earth, the earth itself would probably expirence multiple asteroids hitting the earth with equal or greater size than the one that hit the earth killing the dinosaurs most likely sending us into another ice age due to the climate change caused by the impact. That is just the after effect but the problems that the asteroids would cause as soon as they hit the earth would be astronomical and on a global scale most likely causing the deaths of millions.
  5. Oct 18, 2007 #4

    Jonathan Scott

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    If the moon was somehow cleanly removed without showering the Earth with fragments, then this would have a slight effect on the Earth's orbit but no immediate effect on its rotation. The effect on the Earth's orbit can be understood by considering the Earth and moon as a combined rotating system; if the moon is suddenly removed, the overall momentum of that system is changed by the momentum of the moon in its orbit around the Earth.

    Using figures from the internet, I make it that the mass of the moon is very roughly about 1/80th of that of the Earth, and the relative velocity of the moon in its orbit about the Earth is about 1/30th of that of the Earth about the sun, so the fractional change in momentum of the Earth in its orbit would be about 1/(80*30) = 1/2400. If the change in momentum were aligned forward or backwards along the orbit to maximize the effect on the velocity, then the fractional change in kinetic energy in the orbit would be proportional to the square of this, that is around 1 part in 6 million.

    Another effect of losing the moon would be that ocean tides would be much smaller (something like only 1/3 of the amplitude), as they would only be due to the sun. They would also be locked into a repeating daily cycle with some variations over a yearly cycle instead of changing in time of day and amplitude over a monthly cycle.

    The reduction in the tides would also mean in the very long term that the rate of slowing of the Earth's rotation would be reduced.
  6. Oct 18, 2007 #5
    Hmmm, Is your theory taking into account the removal of the earth moon barycenter? Wouldn't the Angular momentum about the pre-existing BC be transfered as pure kinetic energy depending on when the moon was removed? Wouldn't this somewhat alter the eccentricity of earths sun orbit?? Just curious.
  7. Oct 19, 2007 #6

    Jonathan Scott

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    Not angular momentum, but linear momentum due to the moon's orbit around the Earth. I've assumed as an approximation that its orbit is about the center of the Earth, not about the barycenter of the Earth/moon system which is nearer the Earth's surface, hence the word "roughly". The effect does depend on the point in the orbit at which the moon was removed, and could alter both the eccentricity and overall energy of the orbit slightly.

    Another way to look at it is that the Earth wobbles slightly in its orbit around the sun because of the moon pulling on it. If the moon is suddenly removed, the current direction of the wobble effectively becomes an impulsive change affecting the overall orbit (mainly causing about half of it to be higher and half of it to be lower than before, but also causing a slight change in the overall energy).
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