Astronomers Have Been Predicting New Planets in our Solar System for Centuries

The theoretical planet Tyche’s theoretical orbit. via

For every planet in our solar system there’s a hypothetical planet, some heavenly body that would explain some observed astronomical occurrence. It’s a compelling idea–that our Solar System is filled with unseen masses–which is probably why stories of new planets keep popping up. This week, the planet Tyche (pronounced ty-kee) has reappeared in social media circles. The supposed planet is theorized to be four times the mass of Jupiter and lurk in the outer Oort Cloud, orbiting 375 times farther from the Sun than Pluto. But so far, theories are all we have on this planet. 

Astronomers have been predicting new planets based on mathematical models and observations almost as long as the telescope has been around. It’s how astronomers found Neptune–a body was predicted to orbit outside Uranus to explain its orbit. But some predictions haven’t produced as striking (or concrete) a result as Neptune. 

Tyche isn’t a new hypothetical body. In the 1980s, astronomers theorized that the Sun had a companion. The idea was that if our star was part of a binary system with the unseen companion following a highly elliptical orbit, the sister star would periodically perturb comets in the Oort Cloud and send a shower of comets towards the inner solar system. Some of these icy rocks would slam into the Earth eradicating almost all life. This would explain Earth’s periodic mass extinctions. The Oort-lurking star was appropriately named Nemesis.

But the more scientists study the Earth the more certain we are that mass extinctions don’t happen at regular intervals. The idea of Nemesis was retired, but the potential mass remained. It was renamed Tyche, Nemesis’ benevolent sister, and is thought by some to be a rogue gas giant that was captured by our Solar System. In any case, it’s existence is still up for debate.

Neptune, the original “Planet X.” via

Similar to the idea of a stellar companion to the Sun is the idea of a companion Earth. A body orbiting exactly opposite our own such that it is always blocked from the Earth by the Sun. The companion Earth theory went out the window as we started exploring the inner solar system and failed to find the predicted body. There’s also Nibiru, the theoretical planet on a collision course with the Earth that has yet to be found.

Another long-standing hypothetical planet is Vulcan, a planet once thought to reside inside Mercury’s orbit. An amateur astronomer named Lescarbault reported seeing a round black spot transiting the Sun on March 26, 1859. He thought it was a planet, one too small to explain the observed deviations in Mercury’s orbit but a planet nonetheless. Astronomers tried to find Vulcan during solar eclipses (one in 1869 and one in 1878) but never found solid evidence. Still, reports persisted of astronomers finding disks crossing the Sun, and many believed they were small planets. No spacecraft has ever confirmed these bodies, and it’s thought, in hindsight, that the observed disks were actually comets.

There’s also Planet X. Just like Neptune’s orbit was predicted to explain the irregular orbit of Uranus, Planet X was the theoretical trans-Neptunian planet predicted in 1841 to explain the irregular orbit of Neptune. While Planet X was never confirmed, certain trans-Neptunian bodies do explain the planet’s orbital oddities. Specifically two groups of small bodies that orbit in resonance with the ice giant: one composed of Pluto, 1993 SC, 1993 SB, and 1993 RO, and the second composed of1992 QB1 and 1993 FW. Astronomers called of the search for a trans-Neptunian Planet X in 1992. 

Our current Solar System. via

Along with the theorized planets there have been a host of theoretical moons: Venus’ moon Neith; a moon for Mercury; and additional moons of Jupiter, Saturn, Mars, and Uranus. While no new moons for the terrestrial planets have been confirmed, the few interplanetary missions we’ve launched have confirmed the existence of many new moons for the gas giants. 

So new planets and moons have a history of popping up, and in very few cases have they been confirmed as real bodies. So it’s probably not worth forgetting the order of the planets just yet.