Kirkwood gap
Gaps in asteroid belt due to Jupiter orbital resonances.
The Kirkwood gaps are regions in the main asteroid belt where few asteroids orbit, caused by gravitational tugs from Jupiter. Daniel Kirkwood first identified these gaps in 1866 and correctly linked them to orbital resonances with the giant planet.
Quick Facts
- Discovered by
- Daniel Kirkwood
- Year of discovery
- 1866
- Example resonance
- 3:1 orbital resonance at 2.50 AU
- Main gap locations
- 3:1, 5:2, 7:3, 2:1 mean-motion resonances with Jupiter
Facts from the source article.
Asteroid zones
The Kirkwood gaps are not empty spaces in a quick photograph of the asteroid belt. Because asteroid orbits are elliptical, many asteroids still cross through the same distances from the Sun where the gaps are located. The actual density of asteroids within these gaps is about the same as in the regions next to them. The main gaps are caused by mean-motion resonances with Jupiter: the 3:1, 5:2, 7:3, and 2:1.
For example, an asteroid in the 3:1 gap orbits the Sun three times for every one orbit of Jupiter. Weaker resonances also exist, such as the 8:3 resonance at 2.71 AU, where fewer asteroids are found. The main asteroid belt can be split into inner and outer zones, separated by the 3:1 gap at 2.5 AU. The outer zone is further divided into middle and outer zones by the 5:2 gap at 2.82 AU.
The 4:1 resonance is at 2.06 AU, the 3:1 at 2.5 AU, the 5:2 at 2.82 AU, and the 2:1 at 3.28 AU. The largest asteroid in the inner zone is 4 Vesta. In the middle zone, the largest are 1 Ceres and 2 Pallas. In the outer zone, the largest is 10 Hygiea. Beyond the outer zone, 87 Sylvia is probably the largest main-belt asteroid.
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