How little of gravity before Athletics gives way to Free Fall? Is there a defined border? Would it be reasonable to set one? Is anything with less than 0.1 g microgravity for game purposes, or perhaps less than 0.01 g?
Venus (0.9 g), Mars (0.38 g), Mercury (0.377 g), Luna (0.165 g), Titan (0.138 g), and Europa (0.134 g) all seem like they have enough gravity for Athletics to be the skill dictating movement.
What about Ceres (0.029 g)? It's the lowest surface gravity of significant named objects that I can find. Is 3% of Earth's gravity enough that Athletics would be used, or would this be treated as a microgravity environment requiring Free Fall?