Objects that Collide with Earth

Question: Hypothetical question: We hear about what would happen when the Earth is struck by comets and asteroids; the extinction of the dinosaurs for example or the end of life on our planet for us humans. In its infancy the Earth was struck by another protoplanet and survived the impact that formed our Moon. How large would the object have to be to cause the Earth to disintegrate having been struck by it?  — David

Answer: First, lets set the scale of impact events.  The object that collided with the Earth about 65 million years ago which resulted in the extinction of the dinosaurs was about 10 km is diameter.  Clearly an impact of this magnitude would lead to mass extinction of most species on Earth.  Also, as you pointed out, the most likely theory which explains the formation of our Moon involves a collision with a Mars-sized object early in the formation of the solar system.  Mars is about 3500 km in diameter.  Compare this to the diameter of the Earth, which is about 12,700 km.  So, an object which is anywhere from 5,000 to 10,000 km in diameter contains enough energy to seriously damage, and possibly even destroy, the Earth.

Jeff Mangum


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2 Responses to Objects that Collide with Earth

  1. David Knight says:

    Please may I seek clarification on a question I submitted to you on 01.03.2013. Quote,”The object that collided with the Earth about 65 million years ago which resulted in the extinction of the dinosaurs was about 10 km in diameter.” Does the, “10 km in diameter” refer to the size of the object as it entered Earth’s atmosphere or the size of the object that actually hit the ground?

    Could you please answer a hypothetical question for me to do with our Sun’s magnetic field. My query arose from watching a programme on our Sun by Professor Brian Cox. Using some beautiful animation he described how the Sun’s powerful magnetic field warped gases into arches on the surface of the Sun and hurls out solar flares from the Sun. On the Earth my oil filled army compass settles down until needle points north and south. If I could stand on the Sun’s equator with my compass would the needle point north and south or fluctuate or spin wildly?

    (May I thank Jeff Mangum for the time and trouble he has taken in answering my questions on Astronomy.)

    • Jeff Mangum says:

      Hello David,

      The 10 km diameter refers to the size of the object before it entered the Earth’s atmosphere.

      Regarding your question about the Sun’s magnetic field, I believe it would depend upon exactly where you were standing which would dictate how the needle on your compass behaves. The magnetic field on the Sun is both position and time dependent. I expect that the needle would in fact fluctuate rather than point in a particular direction.

      Jeff Mangum

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