Is it proper to say planet eks or is it planet ten? I’ve always assumed the “X” was a Roman numeral.
I think the International Astronomical Union specifies that it’s the letter X. The B52s agree.
I always thought of it as “The Planet of Scantily-Clad Jogging Blond Aerobic Instructors”, myself.
I thought that was Planet XXX. 
I always try to remember to pronounce the X as the Roman numeral ten, but Planet X sounds cooler than Planet Ten.
Planet ten from outer space just doesn’t have the right ring.
I’ve always presumed it bo be planet “ecks” meaning unknown factor.
I believe the correct pronunciation is “fraud”.
I believe Pluto was reffered to as “Planet X” while they were searching for it, so I think the fact that X is the Roman number 10 is just coincidental. It stands for the unknown, as in the variable x in mathematics.
blink I’ve always thought of it and said it as the letter X. I thought it was a neat that that turns out to be ten, too, but, as Loopus said, Percival Lowell (and proably a lot of other people, too) referred to the then-putative ninth planet as Planet X, too.
No, no… It’s pronounced “Zyt’xlfnordbk!lbtstk” (pardon my Earthling accent).
Actually, a type produced Planet X. It was supposed to have been Planet XX, pronounced “Planet Dos Equis.”
It’s pronounced planet throatwarbler mangrove the X is silent.
If you’re a Mac user, then it’s Planet Ten. If you’re not then it’s Planet Ecks. Your mileage may vary.
I prefer to use Shaggai in lieu of Planet X.