Planet X has a protracted and storied historical past of non-existence. For about 130 years, astronomers have debated the existence of a further planet or planets to elucidate discrepancies within the orbits of the recognized planets (primarily Neptune and Uranus). Later, the record of discrepancies was expanded to cowl trans-Neptunian objects. However not one of the Planet X candidates found, together with Pluto, have the mass or location to elucidate observations.
Primordial black holes have now been proposed as the most recent planet X (or planet 9, since Pluto was demoted).
Planet X’s origin begins with the invention of Neptune. Neptune was not discovered accidentally: observations of oddities within the orbit of Uranus had been used to calculate the placement of Neptune, and it was subsequently discovered.
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