The Kirkwood gap
Daniel Kirkwood (1867)
No asteroids at 2.5 or 3.3 a.u. from sun
2:1 & 3:1 resonance with Jupiter
Jack Wisdom (1981) solved three-body problem
of Jupiter, the Sun and one asteroid at 3:1
resonance with Jupiter.
Showed that asteroids with such specifications
will behave chaotically, and may undergo large
and unpredictable changes in their orbits.