Below this a body is a rock rather than a world, meters.
200 km, not isLandable's 1,000 km. That predicate answers "can a ship put
down here and have somewhere to be", which is a gameplay question; this one
answers "is there enough ground for a descent from orbit to two meters to
pass through every level", which four hundred kilometers of diameter is. The
cut also keeps Enceladus (252 km) and Miranda (236 km) in, and they are two
of the most geologically interesting surfaces there are.