When two masses interact over large distances, the near-Earth approximation $U = mgh$, which uses the gravitational acceleration on the surface of the Earth $g$, no longer applies. Instead, we use the universal form of gravitational potential energy.

For two point masses $m_1$ and $m_2$ separated by distance $r$, the gravitational potential energy is

Here $G$ is the universal gravitational constant, and $r$ is measured between the centers of mass.