Likely orbital period of a moon around an earth-like planet

The important thing here is how the moon formed.

Earth's moon formed in a scenario explained by the Giant Impact Hypothesis:

1. Earth, the inner planets and other small bodies coalesce in the Sun's protoplanetary disk.
2. Over the years, they grow from their diminutive initial states to more planet-like sizes.
3. One day, a large protoplanet nicknamed Theia hits Earth.
4. Material from Theia and Earth is ejected out into space.
5. Some of this material falls back to Earth (which contains part of the now-destroyed Theia).
6. The rest coalesces to form the Moon.

This collision could have happened at a variety of angles and at a variety of speeds, and could have led to a variety of outcomes. The angle of impact was only about 45 degrees. A more direct blow could have destroyed Earth.

Does the distance from the planet govern the speed of the moon's orbit?

Yes. You can calculate it.

Set the gravitational force equal to the centripetal force: $$F_g=F_c$$ $$G \frac{Mm}{r^2}=\frac{mv^2}{r}$$ $$v^2=\frac{GM}{r}$$ $$v=\sqrt{\frac{GM}{r}}$$ That's the velocity in meters per second. You can then find the period (in seconds) by $$T=\frac{2 \pi r}{v}$$ Use SI units for everything.

posted about 9 years ago

HDE 226868‭

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