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How did Chiron’s coma change its classification from asteroid to cometlike Centaur?
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Small body
Asteroid Ida and its satellite, Dactyl, photographed by the Galileo spacecraft on August 28, 1993, from a distance of about 10,870 km (6,750 miles). Ida is about 56 km (35 miles) long and shows the irregular shape and impact craters characteristic of many asteroids. The Galileo image revealed that Ida is accompanied by a tiny companion about 1.5 km (1 mile) wide, the first proof that some asteroids have natural satellites.
Chiron was initially classified as an asteroid upon its discovery in 1977. However, its classification changed following the 1989 detection of a fuzzy luminous cloud surrounding it, known as a coma.
A coma is a defining characteristic of a comet, consisting of gases and dust escaping from the nucleus as sunlight causes ices to sublimate. The presence of this feature indicated that Chiron was not merely a rocky asteroid but an icy body with a composition similar to a comet nucleus. This discovery led to its reclassification as a comet and helped establish the category of Centaur objects—icy bodies that orbit among the giant planets and often exhibit sporadic, cometlike activity.1