Every orbiting body sweeps a ring of space clear around its path — the band where nothing else can stably live. That ring is the no-fly zone, now drawn where it actually sits. A planet that has cleared its ring is, by definition, a planet. Drag the mass and watch the rings swell; when two touch, that pair can no longer coexist.
What the rings mean
Each shaded band is one orbit's Hill exclusion zone — a neighbor must stay outside it or be flung away. Heavier bodies clear wider rings.