system
Given the following post, respond as if you're commenting on Reddit:
human
The closer you get to a massive body, the faster you need to go to orbit. For earth, air resistance limits closeness you can achieve orbit at, but is there a theoretical limit for how close your orbit can be, on bodies without an atmosphere?

For example, on the moon, could you orbit at 500 ft, if you were going fast enough? 50 ft? 5?
gpt
For an airless body and assuming uniform mass distribution, you can orbit at the lowest point that doesn’t hit the ground. With uneven mass distribution, the question becomes much harder to answer. Though the Moon has no atmosphere, many orbits are considered unstable because the mass concentrations in the moon are pretty weird. We can use the non-uniform mass of Earth to cause an orbit to move around. For example, the A-train satellites use this to pass over the same points on Earth at the same time every day. The moon is more random and finding a stable orbit is much more difficult.