Asteroid-Comet Hybrid Discovered to Have Rings

Artist's impression of Chariklo, the largest Centaur asteroid that orbits the sun in the outer solar system, the first such object to be found to possess its own ring system. (PHOTO CREDIT: ESO)
Artist’s impression of Chariklo, the largest Centaur asteroid that orbits the sun in the outer solar system, the first such object to be found to possess its own ring system. (PHOTO CREDIT: ESO)

There is an exclusive group of celestial bodies in our solar system that are known to possess rings. The most famous is Saturn, of course, but Uranus, Neptune and Jupiter also sport some understated dusty rings.

In recent years, however, astronomers have discovered that ring systems aren’t exclusive to the gas giants. In 2011, a small icy minor body in the outer solar system was also discovered to have rings. Chariklo is a centaur, an asteroid-comet hybrid orbiting the sun in a region between Jupiter and Pluto, and its rings were discovered when the object drifted in front of a bright star — an event known as a stellar occultation.

Now a second centaur called Chiron as been discovered to also have rings, revealing that far from being a frozen and inactive subclass of solar system bodies, centaurs may be a lot more lively than thought.

“It’s interesting, because Chiron is a centaur — part of that middle section of the solar system, between Jupiter and Pluto, where we originally weren’t thinking things would be active, but it’s turning out things are quite active,” said Amanda Bosh, of Massachusetts Institute of Technology (MIT) in Cambridge, Mass.

First discovered in 1977, it became apparent that centaurs were, on the whole, fairly dormant. Like their mythological counterpart — which is part man, part animal — celestial centaurs possess qualities of comets and asteroids. They are undoubtedly rocky, dusty objects, but in the 1980′s astronomers noted comet-like activity on the large centaur Chiron.

Since then, brightening events have been spotted on Chiron, linked to jets of material being ejected from the surface by ices being slowly heated by the dim sunlight, subliming vapor into space.

In the mid-1990′s, James Elliot, who was professor of planetary astronomy and physics at MIT at the time, was able to watch a stellar occultation of Chiron and noted its size (approximately 150 miles wide) and discovered evidence for the jets of vapor and dust.

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SOURCE: Discovery News, Ian O’Neill