First double centaurs discovered

Centaurs are a class of icy planetoids orbiting the sun between the outer planets Jupiter and Neptune. They are known for crossing the orbits of our solar system’s large gas giant planets. In 2006, the centaur Typhon became the first one of its kind known to have a companion, now called Echidna. These two icy bodies are now known to orbit each other about every 11 days.

Here’s a report from the outskirts of the solar system about the discovery of the first double centaurs.

Centaurs are a bit like asteroids, and also a bit like comets. They go around the sun in the realm of the giant planets: Jupiter, Saturn, Uranus, and Neptune. American astronomer Charles Kowal discovered the first centaur in 1977. It was 200 kilometers wide – about 120 miles wide – orbiting between the orbits of Saturn and Uranus. Astronomers named this object Chiron, for the mythological son of Saturn and grandson of Uranus.

Since then, astronomers have found dozens of other centaurs. In 2006, they examined 12 centaurs with the Hubble Space Telescope and found two that are double. In other words, what looked like a single object is really two objects orbiting a common center of gravity.

Centaurs have unstable orbits, only a few tens of millions of years. That’s because the gravity of the giant planets kicks the centaurs around. Some centaurs get ejected from the solar system. Others get catapulted closer to the sun and become comets as some of their ice vaporizes in the sun’s heat and forms a tail.

So the discovery of double centaurs suggests that some comets might also be double.

Our thanks today to Research Corporation, a foundation for the advancement of science.

Our thanks to:
Keith S. Noll
Space Telescope Science Institute

December 1, 2006

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