The search for Planet X
In the early 1840’s, our Solar System had seven known planets. At this time, a French mathematician named Urbain Le Verrier, discovered that Uranus’ orbit may have been disturbed by a large unknown planet.
Some years later, in 1846, Heinrich d’Arrest announced the discovery of Neptune. This new planet didn’t fully account for Le Verrier’s calculations, so the hunt for a missing planet resumed.
In 1906, Percival Lowell began a project to search for a planet beyond Neptune, which he dubbed “Planet X”. Lowell hoped that finding a ninth planet would establish his scientific credibility. He was famous for (incorrectly) identifying features on Mars as canals that had been constructed by Martians. Planet X eluded his search.
It wasn’t until January 1930 that a candidate for Planet X was finally discovered by Clyde Tombaugh. Named Pluto, it was later found to be far too small to have much of an effect on the other planets. Pluto was demoted from the rank of “Planet X” long before it lost the status of “planet”.
In the early 1990’s the mass of Uranus was calculated more accurately. The change accounted for Le Verrier’s results and Planet X was no longer needed to explain Uranus’ orbit. At this time astronomers generally accepted that Planet X did not exist.
Planet X, the destroyer of worlds!
Despite little evidence for an unknown planet, theories persist.
One of the most popular is that the dinosaurs were killed off by Planet X. It is based on the idea that extinction events on Earth could be occurring with an interval of about 26 million years. If Planet X were a large planet or a dim star, then it could be disturbing the icy asteroids in the Oort cloud. Some of these snow-balls could be thrown into inner solar system where they could collide with the Earth and ruin everyone’s day.
Comet McNaught in January 2007. Credit: ESO
This snow-ball throwing planet has been appropriately nicknamed “Nemesis”.
Nemesis and friends
A more recent theory to emerge suggests that Planet X may have friends that include Planet Y or even Planet Z. These objects would be larger than the Earth and very far away, at least 200 times the distance the Earth is from the Sun. Pluto is just 29 times that distance.
Certain bodies, such as the dwarf-planet Sedna have orbits that can’t easily be explained without involving an unknown massive object. Whether that object is one or more new planets that orbit our Sun, or caused by an event in the distant past, is not known.
The answer awaits
Our current technology is not capable of easily spotting planets that are a long way from our sun. Detection technologies are rapidly improving, and we will provably know if Planet X is out there, eventually.
I think that we will find something that could be labelled “Planet X”. It was barely 30 years ago that we knew of only 9 planets (now 8) in the entire Universe. Since then we have found that most stars have planets, dim stars drift between the galaxies, and planets wander through space alone. It would not surprise me if a handful of large, distant planets are quietly orbiting our sun.