Astronomy and Space

Planets and Moons

What are Kuiper Belt Objects?

Kuiper Belt Objects (KBOs) are, as their name implies, objects that originate from or orbit in the Kuiper Belt. Only one KBO was known for more than 60 years: Pluto. Many KBOs have been discovered since 1992, however, and the current estimate is that there are millions, if not billions, of KBOs.

KBOs are basically comets without tails: icy dirtballs that have collected together over billions of years. If they get large enough—such as Pluto did—they evolve as other massive planetlike bodies do, forming dense cores that have a different physical composition than the mantle or crust above it. Most short-period comets—those with relatively short orbital times of a few years to a few centuries—are thought to originate from the Kuiper Belt.


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