# Two moons of Earth?

Hypothetically, suppose there is a situation where the Earth's moon gets neatly sliced into two equal hemispheres, and the force responsible for this slicing also creates a distance between the two halves of say, half the (average) distance from the Earth to the Moon, as it originally stood.

Do the two halves revolve around each other? Do they rotate individually? Do they each still revolve around the Earth?

EDIT: The angular momentum of each half after the division is the same as the angular momentum of the moon before the division occurred.

• Unless the force also creates an angular momentum between the two halves so that one orbits around the other, the two halves fall together again and make a really big explosion. Jan 21, 2013 at 18:47
• As Peter Shor hints, this problem isn't well defined. To evolve the system, you need to specify two of (energy | position | velocity | angular momentum) for each object. You've given the initial positions, but it's not clear how fast everything is moving when you are all done rearranging things.
– user10851
Jan 21, 2013 at 21:16
• Noted. Will make the necessary changes. Jan 22, 2013 at 5:50
• Do you really mean that the angular momentum of each half is the same as the original, rather than the angular velocity? If it's the angular momentum then they will each have twice the angular velocity and they will either enter highly elliptical orbits or leave the Earth altogether (I think it's the latter), whereas if it's the angular velocity then they will be in orbits similar to the original one, and the answer is given by Peter Shor's comment. Jan 22, 2013 at 6:00
• Also, you probably know this, but they wouldn't stay hemispherical for very long because rock isn't strong enough to prevent gravity from re-shaping them into more spherical shapes. Jan 22, 2013 at 6:04