The Roche Limit was a scientific principle.

The idea behind the limit was for determining the minimum distance from a planet's center that a "fluid satellite can orbit and remain stable against tidal disruption." If the planet and satellite densities matched equally, the limit was 2,456 times the planet's radius.

Solid satellites could exist within the Roche Limit as rock's tensile strength (of which natual, solid satellites were made) held the satellite together. (TNG video game: Echoes From the Past)