tethering 2 bodies together

Group,

What is involved to tether a guest body to an inhabited host planet?
The guest needs to be close, and rotating independently of the host.
This rotational differential is used to generate energy.

They would be connected at the poles, to be sure, but what type of
flexibility/rigidity/strength might be involved? Is there a practial
limit to the size/distance of the guest sheroid? Imagine a body
earth's size as the host, to keep things familiar.

The secondary question is what is the expected amount of energy
available with a tethered object that has one end of the tether fixed
to the guest, and the other rotating with respect to the host at it's
pole?

Thanks!

Pat