Kirkwood gaps

In astronomy, regions of the asteroid belt, between the planets Mars and Jupiter, where there are relatively few asteroids.

The orbital periods of particles in the gaps correspond to simple fractions, especially 1/3, 2/5, 3/7, and 1/2, of the orbital period of Jupiter, indicating that they are caused by the gravitational influence of the larger planet. The gaps are named after Daniel Kirkwood, the 19th-century US astronomer who first drew attention to them.