Planet X



Planet X is a place-holder name used by astronomers in their search for a planet beyond the orbit of Neptune (or more commonly among astronomers, "Planet Nine", since the demotion of Pluto). They found Pluto, although it was later demoted to a "dwarf planet" when it was discovered to be a part of a larger population of small trans-Neptunian objects. Today, modern professional astronomers searching for new planets beyond Neptune prefer the term "Planet Nine" instead of "Planet X". "Planet X" is also the term favored in several apocalyptic predictions and conspiracies to refer to a hypothetical badass-sounding planet that will kill us all.

In astronomy
In the period when Pluto was still considered a (non-dwarf) planet, the name was used again for any hypothetical trans-Neptunian "tenth planet," with the "X" doubling as the Roman numeral for "10". The discovery of Eris and other objects caused people to realise that there was no good definition of "planet", so they made one… and had to demote Pluto (and to promote the asteroid Ceres, but most people don't seem to give a damn about it).

The existence of additional bodies like Pluto were initially predicted by looking at the orbits of the other planets &mdash; a model with 8 planets didn't seem to stack up against the evidence. If any other significant planets existed, but had yet to be directly spotted, their gravitational effect would be very visible as perturbations in the orbits of the other known planets and would account for the discrepancies then thought to exist between the planets' predicted and observed orbits. As it happened, the errors in observation (and the errors in guessing the known planets' masses) completely accounted for the discrepancies, and no astronomer today believes there are any undiscovered massive bodies perturbing the observed orbits.

However, some astronomers have suggested in January 2016 that the eccentric orbits of some bodies of the Kuiper Belt could be explained by the presence of a (not tenth) planet a bit less massive than Uranus or Neptune and that would move in a very eccentric orbit around the Sun, that would need thousands of years to complete. Note in any case that not all astronomers share that idea, it is entirely hypothetical until and unless we find it, and it has absolutely nothing to do with Nibiru or other similar things.

Conspiracies
In the 1990s and early 2000s, Nancy Lieder claimed that a tenth planet — Planet X — would pass by Earth in 2003, causing cataclysmic events, possibly topped with an alien invasion. After the date passed, the Planet X story became incorporated in the 2012 apocalypse claims. It is supposed to be the same as Zecharia Sitchin's "twelfth planet" Nibiru and the names are often used interchangeably or joined with a slash ("Planet X/Nibiru"), but Sitchin's original prediction was for the return of Nibiru in 2085. There is very little evidence that any planet like this exists.

Hercólubus

 * Main Article: Hercólubus

Hercólubus is another tenth planet, proposed by the Brazilian medium Hercilio Maes and other authors who seemingly copied its "work". The thing was expanded by the LSD user Colombian gnostic Rabolú in a mess that includes insults to scientists, a planet six times as large as Jupiter that will cause a pole shift, volcanic eruptions, as well as an unstoppable deadly epidemic, more insults to scientists, lack of understanding of Newton's law of gravity, even more insults to scientists, descriptions of life and morale of Venusians and Martians, and yet even more insults to scientists.

Supposedly the thing destroyed Atlantis 13,000 years ago, was going to be visible at dawn in 1999, and when it approached to 4 AU would mess with us. As of 2018 2019  2020  2021  2022 now, it seems that either Galactus or Unicron ate it as a snack.

Wormwood
Planet X has been syncretized with Wormwood, the star from the Book of Revelation prophesized to smash into 33% of rivers and springs:

As if that won't destroy us. Also, in post-Iron Age astronomy: a planet is not a star.