Planet X
Theoretical outer world
Planet X is a hypothetical planet believed to exist in the outer reaches of our solar system, beyond Neptune.
The term originated in the late 19th century when astronomers searched for a large body whose gravity might explain perceived irregularities in the orbits of Uranus and Neptune.
Though that search led to Pluto's discovery in 1930, Pluto proved too small to be the predicted Planet X.
The term now refers to any undiscovered large planet in the outer solar system: Astronomers continue searching for Planet X in the Kuiper Belt region.
- NibiruPseudoscientific catastrophe world
- ancient astronautHypothetical prehistoric alien visitor
- TiamatSumerian primordial sea goddess
- doomsday prophecyPrediction of cataclysmic end
- end timesProphesied apocalyptic conclusion
solar system · orbital · trans-Neptunian · mystery · pseudoscience · conspiracy theory · hypothetical · enigmatic · infrared · science fiction · perturbation · deep space · space opera · alien worlds · heliosphere · Nemesis · dark matter · celestial sphere
- Fictional PlanetsTatooine, Arrakis, Krypton, Vulcan, Gallifrey
- debunked beliefsflat earth, phlogiston, spontaneous generation, geocentrism, phrenology
- Space mythsman in the moon, moon rabbit, shooting stars, star signs, zodiac
- Prog MetalTool, polyrhythms
Planet XEarth
Our world
the Moon · inner planets · home planet · Mercury · Mars
- home planetOne's world of origin
- Planet EarthOur inhabited world
- planetary motionMovement of worlds around stars
- planetary bodiesMasses orbiting stars
- save the planet
- dwarf planetsSmall orbiting spherical bodies
planet, planets, planetary, planetoid, planetarium, interplanetary, protoplanet, exoplanet