On February 14, 1996, the enigmatic object Chiron reached perihelion inside the orbit of Saturn and on April 1 will reach perihelion opposition, its closest approach to Earth. Chiron is unusual because it has a detectable coma, indicating that it is a cometary body, but it is over 50,000 times the characteristic volume of a comet, a size more commensurate with a large asteroid, which it was initially assumed to be. Furthermore, its curious orbit is unstable on time scales of a million years, indicating that it hasn't been in its present orbit long. Chiron was the first of four bodies discovered so far with similar orbits and properties. These bodies have been designated Centaurs, after the race of half-man/half-horse beings from Greek mythology, in recognition of their dual comet/asteroid nature. (Chiron is named after the wisest of the Centaurs, the tutor of Achilles and Hercules.) It is believed that the Centaurs may be objects which have escaped from the Kuiper belt, a disk of objects orbiting beyond Neptune. Chiron is showing increased activity as it approaches perihelion. In an effort to coordinate observations and gain an unprecedented view of a possible Kuiper belt body, the Chiron Perihelion Campaign was organized. This page contains information on Chiron and the campaign to observe its perihelion passage as well as links to images of Chiron from various sources.
Images of Chiron taken by Denis Bergeron, 2 and 3 April 1995.
More information available in the caption
After Chiron was first discovered by Charles Kowal on November 1, 1977 (on a photographic plate taken on October 18) and designated 1977 UB, earlier views of the object on photographic plates dating back to the 1895 perihelion were recognized. Images of Chiron near aphelion in 1970 showed that it was bright even at that great distance from the Sun. This along with evidence of a coma as early as 1988 indicated continuing surface activity and coma production at low temperature. This points to super-volatile substances such as methane, carbon monoxide, and molecular nitrogen, which can sublime at these low temperatures from the surface of Chiron, as being the source of the coma.
The Kuiper belt is a hypothetical disk-shaped reservoir of objects of sizes ranging from tiny particles to Pluto or larger sized bodies. It was theorized to exist as early as 1949 as a source of comets additional to the more distant Oort comet cloud. It may also be the origin of Pluto and Neptune's moon Triton. Since 1992, almost 20 objects have been discovered in the Kuiper belt with diameters of 100 to 300 km, leading to estimates that 20,000 to 40,000 such bodies exist in this region. A 1995 Hubble study discovered about 30 objects 6 to 10 km in diameter which may be part of the belt.
The argument that Chiron is an escaped member of the Kuiper belt is based on a number of lines of reasoning. Gravitational perturbations from the giant planets should occasionally force Kuiper belt objects into Neptune-crossing orbits from which they can evolve into orbits like the Centaur's. The similarity in size between Chiron and the discovered Kuiper belt objects makes this a likely source. Asteroids are also in this size range, but the observations of a coma on Chiron appear to rule out an asteroidal origin. The evidence that Chiron still retains super-volatiles which would only persist for long times at lower temperatures than it presently experiences indicates a colder source region, beyond Chiron's present orbit. The data gathered by the Chiron Perihelion Campaign should help determine if Chiron is indeed a former inhabitant of the Kuiper belt.
Observatories involved in this campaign include many major Earth based observatories and proposals have been made for the Hubble Space Telescope. These images of Chiron will be posted here as they are made available, and results from the observations will be reported. Over the next couple of years we will certainly come to better understand the mysterious object known variously as Comet 95P/Chiron or minor planet (2060) Chiron.
Chiron Fact Sheet
Asteroids and Comets Page
Occultations by Chiron - 1990-1995
- Harvard University
List of Centaur Objects - Minor Planet Center
Hubble Observations of Chiron planned for 16 March 1996
- call for concurrent observations.
Request for Chiron Observation Information - from the HST/FOS Chiron observation team (21 August 1996)