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Comet near the Earth

  1. Sep 25, 2010 #1

    A huge meteor can cause to destroy the civilization.
    But let assume that a comet pass by the Earth.
    Can a comet cause such a big destruction without collision?


    Let assume that a comet collide with the Moon.
    This situation can cause such a big destruction on the Earth?


    And in the case of just small perturbation,
    what kind of effects can be detected?
    For example the length of he day can change?
  2. jcsd
  3. Sep 25, 2010 #2


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    A typical comet might mass something like 1e15 kg. This is in the order of 1/100,000,000 the mass of the Moon. A near miss would have no measurable effect on the Earth.

    A direct collision with the Moon would have less of an effect on the Moon's orbit than the variation it already exhibits due to its eccentricity, so again, the effects on Earth would be nil.
  4. Sep 25, 2010 #3
    Depends on how big and how close. Close enough and tidal forces would cause earthquakes, but too close and the comet would break up, with unpredictable consequences. Smaller comets also leave a trail of debris behind them which can cause a meteor storm, though the meteors typically look spectacular without any effect on the ground.

    Debris from the collision can either fall or collide with the Earth, with disastrous consequences, but the comet needs to be large.

    That's very unlikely as the angular momentum of the Earth is very large. Any perturbations will be very small, though probably measurable. If the 'comet' is hundreds of kilometers across - a dwarf planet - then its tidal interaction could cause perturbations of several minutes in a day.
  5. Sep 26, 2010 #4
    It is my firm belief that the Tunguska event resulted because of an airburst of a meteor in the lower atmosphere of the earth.

    A 10 meter meteor can cause an airburst comparable to the fatman nuclear device dropped on japan.

    With the Tunguska event, the blast was directed downward at first and then travelled along the ground in an outward radius. The blast radius was 8 kilometers wide and scorched and laid flat trees. Windows were shattered in villages more than 200 miles from the blast.

    The meteor completely burned up in the atmosphere. So it never impacted the Earth. But, it was extremely destructive, nonetheless, and would have been a horrific tragedy of historic proportions if the blast had occurred over a populated area.
  6. Sep 27, 2010 #5
    I dont want to talk about meteors entering into the atmosphere.
  7. Sep 27, 2010 #6
    It happens many times every day.
  8. Sep 27, 2010 #7


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    What do you want to talk about? The question was pretty vagur.
  9. Sep 27, 2010 #8
    If you are talking specifically about a comet, and you mean that it passes by the Earth but does not enter the atmosphere, then I don't know why you need an answer from us. Why would a comet travelling outside our atmosphere have any impact on humanity other than that it could possibly impact with a satellite?

    Many comets have solid cores of rock in their nucleus. Others are a mixture of rock and ice. Smaller comets with non-solid rock interiors would almost certainly burn up in the upper atmosphere. A larger comet with a solid rock core could produce the same explosion as a similarly sized meteor.
  10. Sep 27, 2010 #9


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    Janus' post #2 anwers any questions about near misses by comets.
  11. Sep 28, 2010 #10
    My question is theoretical for example a very big comet (bigger than real ones)
    without entering the atmosphere can cause such effects.?
  12. Sep 28, 2010 #11


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    Ah. Fiction. Well, all bets are off then, aren't they?

    How big do you want this planetesimal to be? You'll have to start looking at some of the larger asteroids. Ceres is still 1/100th the mass of the Moon.

    How close would you like it to come? Graze the atmo?
    Last edited: Sep 28, 2010
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