Why Does the Moon & Earth Have Different Relationships with the Sun?

[Martin Rattigan]

Why does the Moon keep the same face toward the Earth but the Earth not keep the same face toward the Sun?

 

[D H]

It's tidal locking. Tidal forces are proportional to 1/R³.

The Moon is much closer to the Earth than the Earth is to the Sun. The Moon is also much smaller than the Earth and much lumpier than the Earth. All of these things combine to make the tidal lock time for the Moon an extremely short time (astronomical time frame) while the tidal lock time for the Earth is very, very long.

 

[Martin Rattigan]

I thought that was probably it. Do you know of anywhere that goes thro' the mechanics of that?

OK - I found something thro' Google - Thanks.

 

[Vanadium 50]

Indeed, no planets are tidally locked, and almost all close-in moons are. (I think there is one exception - Hyperion) R³ is the reason.

 

[SHAMSAEL]

I've wondered about this, for a while: Is it correct to assume that, given enough time, any orbiting body will become tidally locked?