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A planet is a star that moves.  Or is it?

Many decades ago, I thought that anything that orbited the Sun had to be a 'planet'. Of course I was wrong. I considered tiny fist sized meteors, were they planets too?  How about comets, are they planets too? 

So then I crafted a theory that they should be massive enough. How massive? I wasn't sure, but astronomers have decided that means massive enough to create a spherical body due to gravity. That makes sense, planets are spherical. For example, Ceres is spherical, and in the news yesterday with organic precursor molecules.

Astronomers couldn't accept Ceres as a planet, even though massive enough and it orbits the Sun. It's in the asteroid belt and all objects in the asteroid belt are asteroids, right?  So a new restriction was developed that the body must clear it's orbit of other objects. You know, like Neptune has cleared it's orbit of Pluto.  Don't those orbits cross? Has the Earth cleared it's path of the Moon?  Eventually it will. Have we allowed enough time for Neptune to clear it's path of Pluto?  How about Ceres, given a billion years, will it clear it's path of the asteroids? Are we too quick to judgment?

I find the technical definition of a planet to be somewhat arbitrary. Over the last two hundred years, it is a maleable definition, merely altered to suit the current set of facts and fashion. The definition is as firm and fixed as a bowl of jello. In other words, not really a definition. What are we to make of the theorized Planet IX, which is recently in the news. Will it require another change in the definition to force it in or out of contention? Will we need to contort ourselves yet again?

Is Pluto a planet? Perhaps we should ask Petronius Arbiter, literally the arbiter of 'Good Taste' in Emperor Nero's court and where the word arbitration comes from.  If Petronius arbitrarily decides it's a planet, then it is! If not, then it isn't. Because, after all, he has the power!!  Or does he?

Brad

PS That was a well crafted letter Frank, and certainly before it's time.  Well played!