Various unknown

astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...

s have been hypothesized throughout

recorded history Recorded history or written history describes the historical events that have been recorded in a written form or other documented communication which are subsequently evaluated by historians using the historical method. For broader world hi ...

. For example, in the 5th century BCE, the philosopher

Philolaus Philolaus (; grc, Φιλόλαος, ''Philólaos''; ) was a Greek Pythagorean and pre-Socratic philosopher. He was born in a Greek colony in Italy and migrated to Greece. Philolaus has been called one of three most prominent figures in the Pyt ...

defined a hypothetical astronomical object which he called the " Central Fire", around which he proposed other celestial bodies (including the Sun) moved.Marco Ceccarelli, ''Distinguished Figures in Mechanism and Machine Science'' (2007), p. 124.

Types of hypothetical astronomical objects

Hypothetical astronomical objects have been speculated to exist both inside and outside of the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

, and speculation has included different kinds of stars, planets, and other astronomical objects. * For hypothetical astronomical objects in the Solar System, see: List of hypothetical Solar System objects * For hypothetical stars, see: Hypothetical star * For hypothetical

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen (hydrogen-1, 1H) into helium in their cores, unlike a main sequence, main-sequence star. Instead, they have ...

s, see: List of brown dwarfs * For hypothetical black holes, see: Hypothetical black hole * For extrasolar moons, all of which are currently hypothetical, see:

Extrasolar moon An exomoon or extrasolar moon is a natural satellite that orbits an exoplanet or other non-stellar extrasolar body. Exomoons are difficult to detect and confirm using current techniques, and to date there have been no confirmed exomoon detecti ...

* For stars, planets or moons whose existence is not accepted by science, see: Planetary objects proposed in religion, astrology, ufology and pseudoscience and Stars proposed in religion * For hypothetical planets in fiction, see:

Fictional planets of the Solar System The fictional portrayal of the Solar System has often included planets, moons, and other celestial objects which do not actually exist in reality. Some of these objects were, at one time, seriously considered as hypothetical planets which were ei ...

Hypothetical planet types

Hypothetical types of extrasolar planets include: , - ,

Iron planet ] An iron planet is a type of planet that consists primarily of an iron-rich core with little or no mantle. Mercury is the largest celestial body of this type in the Solar System (as the other terrestrial planets are silicate planets), but larger ...

, , A planet similar to Mercury (planet), Mercury that consists mainly of an iron core with little mantle. , - , Ocean planet , , A planet whose surface is covered entirely by deep oceans. , - , Superhabitable planet , , A terrestrial planet more habitable than Earth. , - , Tidally detached exomoon , , A planet that was originally a moon but has become gravitationally detached. , - , Toroidal planet , , A planet that is shaped like a

torus In geometry, a torus (plural tori, colloquially donut or doughnut) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis that is coplanar with the circle. If the axis of revolution does not ...

or doughnut. , - , Trojan planet , , A planet that orbits near the or Lagrange points of a more massive object. , - , Vitriolic planet , , A planet with significant amounts of acid.

References

{{Portal bar, Astronomy, Stars, Outer space, Mathematics, Science Astronomy