Planet X
A hypothetical planet in the Solar system, beyond the currently known outermost planetA hypothetical planet in the Solar system, beyond the currently known outermost planet. (The term was applied to Eris for a short while, when Pluto was still considered the ninth planet.)
» Clyde joined the search for Percival Lowell's "Planet X", a planet beyond Neptune.
Meaning
3 sensesA hypothetical planet in the Solar system, beyond the currently known outermost planet. (The term was applied to Eris for a short while, when Pluto was still considered the ninth planet.)
Transpluto, Planet X
Плане́та ХPlanéta X, Плане́та ИксPlanéta Iks
(obsolete)A theoretical planet responsible for reported gravitational perturbations of Neptune's orbit. (This was initially believed to be Pluto. The reported perturbations were an error.)
(obsolete)A theoretical planet responsible for observed gravitational perturbations of Uranus' orbit. (This planet was discovered and is now known as Neptune.)
Examples
1 sentencesClyde joined the search for Percival Lowell's "Planet X", a planet beyond Neptune.
Translations
6 languagesBy meaning 1
By meaning 1
Origin
X represents an unknown as opposed to the Roman numeral for 10 (initially, Planet X wouldX represents an unknown as opposed to the Roman numeral for 10 (initially, Planet X would have been the ninth planet).
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