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Why do astronomers call Kuiper belt objects trans-Neptunian objects?
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Kuiper belt
An artist's rendition of a binary object in the Kuiper belt. The two objects depicted orbit each other at the edge of the solar system.
Astronomers refer to Kuiper belt objects (KBOs) as trans-Neptunian objects (TNOs) because their orbits lie beyond the orbit of the planet Neptune.12
While the Kuiper belt is a specific region of the solar system, the term "trans-Neptunian object" is a broader classification based on the object's orbital distance from the Sun. Specifically, these objects have semimajor axes greater than that of Neptune, which has a mean orbital distance of approximately 30.1 astronomical units (AU). Because these bodies are located at such great distances, they are categorized by their position relative to the outermost giant planet.12