This could be the dumbest question in the world. The answer may be known to everyone else.

If gravity were moderated by a particle with any mass at all wouldn't the momentum imparted by a spinning planet eventually slow a retrograde moon?

I think I've read about "gravitons". And at the time it made sense.

And, wouldn't some gravity be "absorbed" by a moon, so that on the far side of that moon there would be a gravity shadow? Which doesn't happen, I know.

Or is there some other theory as to how gravity acts, or a massless wave/particle which could express it?

The idea of retrograde moons is intriguing. I don't think I've paid any attention to it before, if, indeed, I've read of them. And if these have been around after the first million years, they've been around a long time. And, they may have been retrograding much, much faster a long time ago.

Arf