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.
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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.
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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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Now, using two powerful telescopes on Hawaii (NASA's Infrared Telescope Facility on Mauna Kea and the Las Cumbres Observatory Global Telescope Network at Haleakala), Bosh's team was able to precisely measure another occultation event in 2011, revealing even more detail in Chiron and the space surrounding it. Their reseach has been published in the journal Icarus.
"There's an aspect of serendipity to these observations," said Bosh. "We need a certain amount of luck, waiting for Chiron to pass in front of a star that is bright enough. Chiron itself is small enough that the event is very short; if you blink, you might miss it."
After analysis of these occulation data, the researchers revealed a surprise - two sharp, symmetrical features were detected before and after the few minutes that Chiron blocked the light of the distant star. These features could be interpreted as a ring system, two bands 3 and 7 kilometers wide with a radius of 300 kilometers from the center of the centaur, adding detail to Elliot's original observations in the 1990′s.
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Although these new observations could provide evidence of rings, there's other possibilities, including a shell of debris surrounding Chiron or they could just provide further evidence for Elliot's active jets ejecting material from the object's surface. Although further observations of Chiron occultations are needed, if this is solid proof or rings around Chiron, it provides tantalizing clues as to the dynamics of this cold region of the solar system.
"Centaurs may have started further out in the solar system and, through gravitational interactions with giant planets, have had their orbits perturbed closer in to the sun," said co-author Jessica Ruprecht, also from MIT. "The frozen material that would have been stable out past Pluto is becoming less stable closer in, and can turn into gases that spray dust and material off the surface of a body. "
"Until Chariklo's rings were found, it was commonly believed that these smaller bodies don't have ring systems," added Bosh. "If Chiron has a ring system, it will show it's more common than previously thought."
Source: MIT via Physorg.com