Discovered in 1977 and initially classified as an asteroid, Chiron was the first recognized member of the Centaurs, a new class of Solar System objects. The Centaurs inhabit short-lived orbits between the asteroid belt and the Kuiper belt, a distant region of icy bodies beyond Neptune. These objects are believed to be scattered from the Kuiper belt by the gravitational influences of the giant planets, akin to a pinball in an arcade machine.
Most Centaurs are expected to 'bounce' around the Solar System for about 10 million years before being ejected, with only a few becoming short-period comets. Among them, Chiron has been particularly notable. It is one of the largest Centaurs and exhibits comet-like activity, including the formation of a fuzzy, dusty atmosphere. Recent observations suggest it may even have a double icy ring.
Despite decades of study, Chiron continues to puzzle astronomers. Recent developments have only heightened interest.
In 2021, astronomers at Queen's University Belfast noticed Chiron's unexpected brightness in the night sky, based on data from the Asteroid Terrestrial-impact Last Alert System (ATLAS). This network of robotic telescopes scans the night sky for potential asteroid impacts. They observed that Chiron was reflecting significantly more sunlight than in the previous five years, a change that occurred while it was behind the Sun and not visible from Earth for over five months.
Dr. Matthew Dobson, a PhD student at Queen's, led a team to investigate this phenomenon. Their findings are detailed in a new paper in The Planetary Science Journal. Dobson stated, "The aim of this study was to figure out what caused the change in Chiron's brightness, was it the rings, sudden cometary activity, a new exposed part of the object facing the Earth?
"We combined historic data and examined observations from on-going surveys that had observed Chiron to test these theories. We also used the Gemini Observatory telescope, one of the largest telescopes in the world, to uncover as much as we could."
The study concluded that Chiron had experienced an increase or outburst of cometary activity. Despite the absence of a visible coma, which is typically a sign of a comet, the researchers hypothesize that the coma could be too faint or held close to Chiron by its weak gravity. The increased brightness was attributed to additional dust around Chiron.
Dr. Meg Schwamb, a co-author from Queen's, commented, "Most searches for activity look for the telltale signature of a fuzzy coma around the object. This paper examined the long-term brightness trend of the object over time, and we believe this technique will be crucially important as the next generation of Solar System discovery and monitoring surveys, such as the Legacy Survey of Space and Time, come online in the next few years."
Dr. Charles Schambeau of the University of Central Florida, who led the Gemini observations, added, "The technique utilised with the extensive ATLAS data enabled the detection of Chiron's activity onset, which was later corroborated by observations from the JWST by an independent team that revealed a conspicuous fan-shaped coma. Consequently, Dr. Dobson's method for identifying activity, even when traditional approaches suggest inactivity, can be confidently extended to study additional objects in the future."
Research Report:The Discovery and Evolution of a Possible New Epoch of Cometary Activity by the Centaur (2060) Chiron
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