Sciency Words: Kirkwood Gaps

Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at the term:

KIRKWOOD GAPS

Some of the asteroids in the asteroid belt have gone missing.

The asteroid belt begins at a distance of 2.1 AU (astronomical units) from the Sun and stretches all the way out to 3.5 AU from the Sun. But there are empty regions at approximately 2.5 AU, 2.8 AU, 3 AU, and 3.3 AU. These empty regions are called Kirkwood gaps.

Kirkwood gaps are named after Daniel Kirkwood, the astronomer who first discovered them and correctly deduced what caused them.

Any asteroid orbiting the Sun at a distance of 2.5 AU would happen to be in a 3:1 orbital resonance with the planet Jupiter. This means Jupiter would complete exactly one orbit for every three orbits the asteroid completed. The 2.8, 3, and 3.3 AU distances happen to correspond to other orbital resonances with Jupiter.

Asteroids in these resonant orbits would experience nagging, persistent gravitational tugs by the Solar System’s largest planet. This would slowly drag them away from their original circular paths around the Sun and throw them into new, highly eccentric orbits.

Many of the asteroids that cross Earth’s orbital path are probably former residents of the Kirkwood gaps. So the next time an asteroid comes along and wipes out the dinosaurs, don’t get mad at the asteroid. It might not be the asteroid’s fault.

Get mad at Jupiter.

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Today’s post marks the end of asteroid belt month for the 2015 Mission to the Solar System… and the beginning of Jupiter month!