Chiron (astronomy)

Chiron (astronomy), small comet-like body that orbits the Sun as a centaur object between the orbits of the planets Saturn and Uranus. Centaur objects are made of ice, dust, and rock, and come from the Kuiper Belt in the outer solar system beyond Neptune.

Chiron completes one revolution around the Sun every 51 years. Its eccentric orbit takes it from a distance nearest the Sun (perihelion) of about 8.45 AU to a farthest distance (aphelion) of about 19 AU, for an average distance of about 13.7 AU. An astronomical unit (AU) is the distance between Earth and the Sun, or about 149,600,000 km (92,956,000 mi). Chiron’s path crosses inside the orbit of Saturn.

Chiron is roughly spherical in shape with a diameter of about 142 km (88 mi). Its rotation period is 5.9 hours. Its highly porous surface is covered in water ice and darker material that likely contains carbon compounds. Chiron has a grayish appearance and reflects only about 11 percent of the sunlight that reaches it, making the object slightly darker than the surface of the Moon.

In January 1995 scientists reported detecting an envelope of gas and dust around Chiron, similar to the coma of a comet, but held in place by gravity from the large body. Other observations have documented different levels of cometary activity on Chiron over time. In some cases, astronomers have found old photographs that recorded Chiron long before it was recognized as a special object. Calculations suggest at some time in the future Chiron could move into the inner solar system to become a short-period comet. Short-period comets have orbital periods of 20 years or less, and are influenced by the gravitational pull of the planet Jupiter.

The American astronomer Charles Kowal discovered Chiron in 1977 and originally classified it as a large asteroid. It was named Chiron after the most notable of the centaurs, half-man, half-horse monsters in Greek mythology. The object is officially known as 2060 Chiron and is listed in the catalog of minor planets. It is also listed as a comet with the name 95 P/Chiron.