Hypothetical astronomical object

Artist's concept of Earth, orbited by a hypothetical second moon
31 Crateris, a possible eclipsing binary initially mistaken for a moon of Mercury
Artist's concept of a carbon planet. The surface is dark and reddish from hydrocarbon deposits.
Artist's conception of HD 209458 b, a possible Chthonian planet, transiting its star

Various unknown astronomical 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.[1]

  1. ^ Marco Ceccarelli, Distinguished Figures in Mechanism and Machine Science (2007), p. 124.