In 1846 when there were only eight known planets, French mathematician Urbain Le Verrier predicted from the irregularities in Uranus's orbit that another giant planet was out there somewhere. Then in September of that same year astronomers from the Berlin Observatory made telescopic confirmation of Neptune (which had actually been sighted earlier by the likes of Galileo and other scientists although they were not sure what they spotted). However, the discovery of Neptune did not settle all of the discrepencies that appeared to be occurring in Uranus's orbit. This is why in 1906 tycoon Percival Lowell began the search for another new planet, one he called Planet X.

When Pluto was later discovered in 1930, this put the idea of Planet X to rest but not fully because the dwarf planet, as we now know it, was just too small to make that kind of impact on the ice giant that is Uranus. However, when Voyager was sent into space a half a century later, its measurements determined that the observed irregularities of Uranus and Neptune's orbits were due to an overestimation of Neptune's mass.

Fortunately, Planet X never managed to be far from the space exploration research field. In 1980, it was proposed that an unseen brown dwarf star could cause periodic extinctions on Earth by triggering outbursts of comets, and in 1990, it was suggested that another Jupiter-sized planet existed along the solar system's edge to explain where certain comets where coming from. Claims of Planet X were once again brought forth at the end of 2015, when claims that a faint microwave glow of an outsized rocky planet around 300 AU (astronomical units – the distance from the Earth to the Sun; approximately 150 million km) away was detected.

One of the most hopeful pieces of evidence that a Planet X might truly exist is Sedna. Disovered in 2003 by Mike Brown of the California Institute of Technology, the same scientist that killed Pluto, Sedna is an object slightly smaller than Pluto and Eris located 76 AU away, which is far outside the reach of Neptune's gravity. This means that something massive had to have pulled Sedna into its own orbit.

Although when it was first discovered, there were many theories as to what could have pulled Sedna away, including a passing star or stellar nurseries. However, since its discovery, five other oddities have been discovered in the same viscinity. This concluded Brown and Konstantin Batygin, also of Caltech, to rule out stars as the unseen influencing factor, stating only a planet could cause these strange orbits.

The two believe that the clustering of these six objects is only a 0.007% chance, or 1 in 15,000, of being a coincidence. Instead they are saying this is proof that Planet X, or Planet Nine as they are now calling it, a planet they believe to be the size of Neptune (because the Wide-field Infrared Survey Explorer would have detected anything the size of Saturn or larger) and orbits the sun once every 15,000 years, exists.

“Killing Pluto was fun. Finding Sedna was scientifically interesting, but this one,” stated Brown in Science, “this is head and shoulders above everything else.”

Now, Brown and Batygin believe they just have to wait to for Planet X to appear on a telescope viewfinder to have undeniable proof. They will be using one large telescope out of Hawaii to continue to look for the planet but are also calling on other astronomers to join in their hunt.

If Brown and Batygin are right, then all those that are still upset about Pluto's reclassification can rejoice that there will once again be nine planets in our solar system.