> Why are the rocks in the centre "fused together"? Gravity.
That's what fused them in the first place but they hold together on their own now. Like an asteroid - it's a big rock, gravity is not the force holding it together.
Unlike the earth which has a liquid core, as far as I know the moon is a single solid chunk of rock. So the Roche limit is not an accurate measure - you need to take into account the tensile strength of rock.
> The point you make about the tidally-locked orbit doesn't hold. Tidal forces are there whether or not the object is tidally locked.
You misunderstood me. In a rotating body the tide would cause the object to flex on every rotation, given enough time it would surely break apart from material fatigue.
But in a tidally locked body the force is applied once (a stretching force) and stays that way, so there is no fatigue - either it's strong enough or it's not.
That's what fused them in the first place but they hold together on their own now. Like an asteroid - it's a big rock, gravity is not the force holding it together.
Unlike the earth which has a liquid core, as far as I know the moon is a single solid chunk of rock. So the Roche limit is not an accurate measure - you need to take into account the tensile strength of rock.
> The point you make about the tidally-locked orbit doesn't hold. Tidal forces are there whether or not the object is tidally locked.
You misunderstood me. In a rotating body the tide would cause the object to flex on every rotation, given enough time it would surely break apart from material fatigue.
But in a tidally locked body the force is applied once (a stretching force) and stays that way, so there is no fatigue - either it's strong enough or it's not.