Does the solar system have eight planets?

Connor Haley, who was recently wondering about the definition of fruit, has now turned to more celestial matters. It is true that are only eight planets in the solar system where there used to be nine, not as the result of interplanetary catastrophe but the stroke of a pen that changed the meaning of the word “planet”.

Now that hardly seems fair. Who are they to go and redefine a chap’s words? The shadowy cabal behind this decision are the International Astronomical Union, or IAU, which it turns out aren’t concerned so much with tea breaks and overtime for astronomers and allied trades but more with the names of celestial objects.

There used to be nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. But there are a lot of other things flying around out there, too, like asteroids, comets, the contents of the Kuiper belt and the hypothetical but ominously named Oort cloud.

Pluto always was a bit of a black sheep, bucking several planetary trends. Starting late last century new discoveries revealed a number of other objects that were much more like Pluto than the likes of our own little rock. If Pluto remained a planet then these newly discovered bits and pieces would be planets, too, leaving the definition so broad as to be useless. So, like a club tightening its rules to keep out the nouveau riche, in 2006 the IAU adopted a strict definition that left Pluto out in the cold (and boy is it cold out there past Neptune). Pluto is now officially one of several dwarf planets.

Poor old Pluto — but remember that it was only discovered in 1930 and most people have never actually seen it (it’s too faint to see with the naked eye). There are people alive for whom the IAU is just going back to the good old days.

There are eight planets, with good reason. You may still harbour nostalgic feelings for Pluto, but if you like it so much why don’t you go and live there? Heavens above, it’s just a rock!

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