Sciency Words: Planet X

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Today’s post is part of a special series here on Planet Pailly called Sciency Words.  Every Friday, we take a look at a new and interesting scientific term to help us all expand our scientific vocabularies together.  Today’s word is:


Planet X is the name given to any hypothetical planet yet to be discovered in our Solar System.  Percival Lowell originally coined the term back in the early 1900’s.  Lowell is the same astronomer who thought he saw canals on the surface of Mars, “proving” the existence of a Martian civilization.

At one time, Uranus and Neptune could have born the Planet X title.  Scientists long suspected the existence of a seventh planet due to anomalies in the orbit of Saturn.  After Uranus was discovered, anomalies in its orbit hinted at the existence of Neptune, and anomalies in Neptune’s orbit hinted that there might be even more planets beyond it.

Recent data from the Wide-Field Infrared Survey Explorer, a.k.a. WISE, found no evidence of a Planet X, which seemed to put the matter to rest once and for all.  There are lots of dwarf planets out there, like Pluto and Eris, but nothing large enough affect Neptune’s orbit in any meaningful way.

Now NASA scientists are proposing the existence of Planet X again to explain anomalous perturbations in the orbits of two of the most distant known dwarf planets.  To be fair, WISE failed to detect any Saturn or Jupiter-sized planets.  This new Planet X would be much smaller, closer to the size of Earth or Mars.

It seems our Solar System just keeps getting more and more crowded.

9 Planets

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