Sunday, December 07, 2008

What if... #7

What if the Earth had two small moons instead of one?

This post is part of the 2008 advent series "What if..."


  1. The obvious effect would be more complicated tidal patterns. Exactly how this would turn out would depend on the relative sizes, eccentricity and inclinations of the orbits. Some tides would be much more pronounced than others.

    Hopefully the orbits would differ enough in radius that the interaction between the moons would be neglible. Otherwise it is likely that the system would be unstable in the long run. Which could have very unpleasant consequences.

  2. Without the moon the earth's rotational axis would not be nearly as stable over long time periods. Human civilization could not have arisen if the Earth tumbled so much that Europe ended up at the pole every few hundred thousand years.

  3. -Neil Armstrong would have had to make two small steps

    -We could possibly have more solar eclipses

    - We would be better protected from incoming space debrise so the dinosaurs might still be roaming the planet

    - There would be twice as many full moons thereby doubling the number of lunatics.

  4. We might have discovered the laws of motion and gravity earlier?

  5. Obviously NASA would of had 2 moon landings to fake instead of one... (-:

  6. Women's menstrual cycles would be even more complicated.

  7. Thanks for the comments...

    There would be no months ;-), perhaps no week, and a very different calendar. I wonder if the heavens then would have been even more confusing? Perhaps special close encounters of the Moons in the sky would have been considered very important events?

    And indeed, no big tides... and I had something in mind as Laskar's Stabilization of the earth's obliquity by the moon. Actually, as Johan and Anonymous have pointed out, long-term stability seems to be quite a problem without a moon as we have it.

  8. Then Earth would be called Mars!

    Stefan, indeed there is some work to indicate that the orientation of the spin vector (i.e., obliquity) of Mars may be chaotic.

    Whether the obliquity of a hypothetical Earth with two small moons becomes chaotic or not would probably depend to a large degree on the masses of the two small moons...

  9. Hi changcho,

    thanks for the links - that's interesting!

    Now, the Mars moons are really small... Reading the Wikipedia entry: Deimos looks more like a bright star or planet for an observer on Mars, only slightly bigger than Venus looks from earth I wonder if the little green men called this tiny thing a moon at all ;-)

    Cheers, Stefan



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