I always learned Pluto is a planet. But now I hear it isn’t. What gives?

Our answer:

Ever since its discovery, Pluto has been something of an enigma and a source of disagreements between astronomers. A small rocky body where they’d expect another gaseous one like the four planets preceding it. Today, Pluto is no longer listed as a planet, and all the old textbooks on this issue are considered out of date. Does it matter? Not all that much – but if we’re even considering a question like this, then we must first understand what “planet” actually means.

  1. “Planet” comes from the Greek word for to “wander”. That’s because when you track the movements of stars at night, you’ll note that all stars “move” in a regular, predictable pattern, while SOME “stars” zigzag back and forth, “wandering” the night sky seemingly aimlessly. So, “planets” were all those stars which moved erratically. It’s for this reason that Pluto, once first discovered, was declared a planet.
  2. Pluto is tiny. And it zooms through space accompanied by thousands of other almost as large celestial bodies (we know that since Eris, a trans-Neptunian body of a greater size than Pluto was discovered in 2005). You may thus think of Pluto as one of the largest asteroids in the asteroid belt. If you were to pick one and single it out as a planet – what about the others?
  3. Astronomers have since refined the notion of “planet” as not merely a celestial object moving in an elliptical orbit around a star, but also one which needs to be “massive enough”, must be round due to its own gravity, and must fly alone – not accompanied by other bodies going the same way along roughly the same orbit.

Even by the updated definition, Pluto CAN still be considered a “planet” – even if at a slight stretch. Still, it’s the astronomers that must deal with this matter, not us poor darkies, so if they don’t WANT it to be a planet – it ain’t. So the answer is: NO it’s not a planet, strictly scientifically speaking. But YES, it is a planet – if you want it to be.

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