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QUICK – how many planets are there in the solar system? If you were born in the 20th century, the answer on the tip of your tongue might be nine. Of course, the official answer is eight, ever since an International Astronomical Union vote in 2006 that ejected Pluto from the line-up.
One issue was that if Pluto had been allowed to remain a planet, it would have meant admitting many other Pluto-like bodies to the planetary roster. The group ultimately opted to keep the solar system neat and tidy, dumping Pluto and its ilk in a box marked “dwarf planet”.…