Phaethon, the hypothetical fifth planet that has never been found between Mars and Jupiter

Throughout history, astronomers have postulated the existence of certain planets in the Solar System that have never been found.

Three possible dark stars have been detected, a celestial body that was only a hypothesis
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An example of this is the planet Vulcan, a hypothetical planet that would be located between the Sun and Mercury . Some reputable astronomers even claimed to have seen it in the 19th century, until its existence was ultimately ruled out. Likewise, there have been cases of celestial bodies, such as Ceres, in the Asteroid Belt, or Pluto, in the Kuiper Belt, which were initially considered planets until the category of dwarf planets was created for them.

A hypothetical planet about which many theories have circulated (and still continue to circulate) is Phaethon, a supposed fifth planet between Mars and Jupiter. Its existence was postulated by the German astronomer Heinrich Wilhelm Matthäus Olbers (1758-1840), as a theory to explain the existence of the Asteroid Belt. To this day, Phaethon has not been found, so his possible existence remains a mere hypothesis. On this issue, the channel V101 Space published an interesting video this Friday:

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Image: IGN.