Expert: Jayendra Upadhye - 5/9/2008

Question
Thank you for your enlightening answer.  I had thought that the lack of atmosphere on the moon was due to the earth's gravity.
If you don't mind, may I ask a few more questions: What impact would the planet be likely to have on its satellite? Would the smaller body necessarily fall into a synchronous orbit? The planet as viewed from the moon would have varying phases. Is that correct?  
Thank you so much,
Mary

Answer
Hi,
Mary I do hope you did not forget the critical part of rating my answer. Many people just "get their answer" and disappear!

Yes ofcourse ask as many questions as you wish.
[ref:-http://en.wikipedia.org/wiki/Moon
This site explains it all.
1 - lunar recession under para "Orbit and relationship to Earth".
2 - same para shows the earthrise photo by apollo 8 where the earth shows "half moon" phase!]

That side, The foremost impact a bigger body (mass wise) has on its satellite is called "tidal phase locking".
[ref:-http://en.wikipedia.org/wiki/Tidal_locking].

All the gas giants and their moons follow this rule. (rather most of them do).
This law states that the smaller satellite body will end up pointing one face to the main planet that it is orbiting. Our moon follows that rule too.
Yes! In spite of the phase locking of the satellite, the planet would continue to show phases when viewed from the satellite.
[the famous "rising earth" picture by the Apollo astronauts showed earth displaying this phenomenon when it appeared hanging just over the moon's horizon].

The mechanism of phase locking is fairly well understood. You see any other state of the satellite, makes a tidal deformation travel along the line joining centers of both bodies, "travel all along the satellite's surface, heating it up / dissipating its rotational momentum. This happens essentially due to a differential (non-synchronised) rotation of the satellite (causing travel of the bulge) and the differential in gravitational acceleration of the parent body from the farthest end of the satellite to the nearest end (causing the bulge in the first place).
[The dissipative effect is akin to trying to ride a bicycle with less air in the tyres! it causes more effort, as the deformation travelling along the tyre surfaces as they roll, disspates energy.
the more the deformation, the greater the effort].
In satellites, the greater the gravity gradient and differential speed at the surface, greater is the braking effect.  

The consequnce is also on the main planet, but lesser in degree due to its greater mass.

Another consequence is that due to this sort of gravitational coupling, the satellite speeds up and the main planet speeds down!

The increased orbital speed catapults the satellite to higher orbital distance. The moon currently is receding from earth 4 cm / year due to this gravitational slingshot effect.
[refer:-http://en.wikipedia.org/wiki/Tidal_acceleration]

The last class is of satellites too close to their parent (Roche limit), in these satellites, the gradient of gravitational acceleration across their bodies becomes so great, it tears the satellite apart! Something that happened to one saturn's satellite, resulting in the rings.
[refer:-http://en.wikipedia.org/wiki/Roche_limit].
 
Please do rate the answer if you find it helpful.
hope that suffices,
regards
Jayen