• Question: how long till the moon falls out of orbit

    Asked by js109345 to Austin, Kirsty, Nicola, Nike, Sarah on 19 Jun 2012.
    • Photo: Kirsty Ross

      Kirsty Ross answered on 19 Jun 2012:

      Actually, the moon is moving away from the earth at a rate of about 2.5cm a year. This is due to the earth’s rotation slowing due to friction from the tides. To make up for that, the moon is moving away from the earth. Eventually the earth’s rotation will slow to the point that it matches the rotation of the moon around the earth. At that point the earth and moon will constantly present the same face to one another and the moon will stop receding.

      However, this slowdown of the Earth’s rotation is not happening fast enough for it to get to that point. About 2.1 billion years from now, the continual increase of the Sun’s radiation will cause the Earth’s oceans to boil away – that will remove the bulk of the source of tidal friction. Even without this, 4.5 billion years from now the Sun will evolve into a red giant and likely destroy both the Earth and Moon.

    • Photo: Austin Elliott

      Austin Elliott answered on 20 Jun 2012:

      Hmm. 2.1 Billion years until the oceans boil away – sounds a good long way off..!

      I think we can be pretty sure we won’t be around…! The earth is about 4.5 Bn years old, and humans have only been around for a tiny, tiny bit of that time, as Kirsty and I discussed over here.

      Great ans, BTW. I never knew that about the earth and the moon moving apart.

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