Planet Nine hypothetical planet Actions Share Share Share to social media Facebook X URL https://www.britannica.com/science/Planet-Nine Share Share Share to social media Facebook X URL https://www.britannica.com/science/Planet-Nine Also known as: Planet X, ninth planet Written by Fred Frommer Fred Frommer is a sports historian, author, and writer who has written for a host of national publications. Fred Frommer Fact-checked by The Editors of Encyclopaedia Britannica Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors. The Editors of Encyclopaedia Britannica Last Updated: Sep 18, 2024 • Article History Table of Contents Also called: Planet X (Show more) Planet Nine, hypothetical ninth planet in the far reaches of the solar system, further from the Sun than Neptune, the eighth and most distant planet. The Kuiper belt is a flat ring of icy small bodies that revolve around the Sun beyond the orbit of Neptune that is thought to be the source of most of the observed short-period comets. In 2014 some Kuiper belt objects (KBOs) were found to be moving in similar orbits. American astronomers Michael Brown and Konstantin Batygin postulated in 2016 that the similarity in orbits could be caused by the presence of a planet with ...(100 of 342 words)

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