Hypothetical astronomical object
A hypothetical astronomical object is an astronomical object (such as a star, planet or moon) that is believed or speculated to exist but whose existence has not been scientifically proven. Such objects have been hypothesized throughout recorded history. For example, in the 5th century BCE, the philosopher Philolaus "defined a hypothetical astronomical object which he called the Central Fire", around which he proposed other celestial bodies (including the Sun) moved.
Types of hypothetical astronomical objects
Hypothetical astronomical objects have been speculated to exist both inside and outside of the Solar System, and speculation has included different kinds of stars, planets, and other astronomical objects.
- For specific hypothetical planets in the Solar System, see: List of hypothetical Solar System objects
- For specific hypothetical extrasolar planets see: List of unconfirmed extrasolar planets
- For hypothetical stars, see Hypothetical star
- For hypothetical brown dwarfs, see: List of brown dwarfs
- For planets whose existence is not accepted by science see: Planetary objects proposed in religion, astrology, ufology and pseudoscience
- For hypothetical planets in fiction see: Fictional planets of the Solar System
A hypothetical planet or hypothetical planetary object is a planet or similar body whose existence is not proven, but is believed by some to exist.
- For hypothetical planets in the Solar System, see: List of hypothetical Solar System objects
- For hypothetical extrasolar planets see: List of unconfirmed extrasolar planets
Hypothetical types of extrasolar planet include:
- Carbon planet: a terrestrial planet composed primarily of carbon, rather than silicon
- Chthonian planet: A hot Jupiter whose outer layers have been completely stripped off by its parent star
- Coreless planet: A terrestrial planet that has no metallic core
- Goldilocks planet: A terrestrial planet that lies at just the right distance from its star to support life
- Helium planet: a gas giant planet formed around a white dwarf star that is composed mainly of helium instead of hydrogen
- Iron planet, a planet like Mercury that consists mainly of an iron core with little mantle
- Ocean planet: A planet whose surface is covered entirely by deep oceans
- Rogue planet: A planet not tied to any star, but wandering freely through the galaxy
- Trojan planet: A planet that orbits with a star instead of around it
A hypothetical moon or hypothetical natural satellite is a natural satellite that is believed by some to exist, but whose existence has not been scientifically proven.
- For hypothetical moons in the Solar System, see: List of hypothetical Solar System objects
- For extrasolar moons, all of which are currently hypothetical, see: Extrasolar moon
- For moons whose existence is not accepted by science see: Planetary objects proposed in religion, astrology, ufology and pseudoscience
- Marco Ceccarelli, Distinguished Figures in Mechanism and Machine Science (2007), p. 124.