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  Hypothetical Planets :  
 

 

Hypothetical planets are planets whose existence has not been verified but are based on scientific observations and theories of the universe. There have been six major hypothetical planets Counter-Earth, Fifth Planet (Phaeton/Planet V), Planet X, Theia and Vulcan. Counter-Earth, Phaeton and Planet X have been discounted by updates in scientific knowledge but it is still unknown whether Planet V and Theia existed or not.

Counter-Earth was proposed by the philosopher Philolaus in the fourth century BC. It was believed a planet like Earth but located on the opposite side of the Earth's orbit was required to balance the Earth. Since the discovery of gravity and our ability to view the area from space the idea of Counter-Earth has been abandoned.


The planet Vulcan was proposed in the nineteenth century and believed to be located between Mercury and the Sun. Observations of Mercury's orbit showed some attributes that did not make sense so the idea of Vulcan was raised as a possible reason. In the twentieth century these anomalies were explained by Einstein's Theory of Relativity so the idea of Vulcan has been abandoned.

A fifth planet between Mars and Jupiter has been proposed in the eighteenth century and again in 2003. Phaeton was believed to have resided between Mars and Jupiter. When the asteroid Ceres was discovered in 1815 it was thought to be the missing fifth planet. After the discovery of the asteroid belt scientists believed that Phaeton had exploded and the asteroids were the remnants of the planet.

We now know that asteroids are formed through accretion so Phaeton has been disproved. In 2003 two NASA scientists proposed a fifth planet had existed after computer simulations showed it was possible. This premise has not been discounted but there is not enough evidence to prove it. 
 

 
  Did you know:
  Theia is believed to have been a planet that existed 3-4 billion years ago before colliding with Earth and creating the moon. This theory, known as the Giant Impact Hypothesis, is currently favored as the most likely theory for the formation of the moon. As yet it has not been proven so Theia remains an hypothetical planet.

In the future there will be many more hypothetical planets as scientists attempt to learn more about how the universe works. As our understanding of the universe grows so does our knowledge of whether hypothetical planets are real or not.