Some charts explaining why Pluto is not a "planet"
Okay, I looked around but I couldn’t find a good post that visually expressed why Pluto isn’t a planet so I threw this together fast and I apologize in advance for any inaccuracies. Let me know and I’ll fix them..
I’m sure most of you have seen a poster like this at some point in school, with Pluto in it’s proper place as the ninth planet.
But the thing is that map isn’t accurate to the actual orbits of Pluto.
In reality it’s something more like this.
By the way, notice how the red line crosses the orbit of Neptune?
Pluto wasn’t actually the ninth planet from 1979 to 1999, but the eighth.
Makes the memory trick you learned as a kid a little more complicated if you grew up in that period.
(I was in early elementary school myself when Pluto crossed over which is how it was brought home to me early how strange Pluto was compared to the other planets.)
However, even those charts don’t fully express how different Pluto’s orbit is.
Yeah, Pluto is not only elliptical, it literally orbits on a different plane than the rest of the planets. Most are close to the same plane as the Earth with the exception of Mercury, and to my understanding Pluto is more than twice that.
However it’s not just the revolutions around the sun that are strange. A large part of this is because of how large the moon Charon is compared to Pluto and how much mass it possess as well.
(As a side-note— Please pay attention to how Pluto’s diameter is about half the width of the US. Let that sink in. It’s smaller than Earth’s moon even.)
In any case, that size affects how they orbit each other.
This is an example of the type of orbit the Earth and our moon have with each other, with the the earth staying in the center of gravity.
This is more along the lines of what Pluto and Charon have, with the center of gravity in the space between the two bodies.
In fact, because of that orbit and the size factor there’s been some debate to classify Pluto as a double planet, and they are sometimes listed as combined Pluto-Charon system.
More than anything though, the changes in the classification come from us knowing more than we did when Pluto was discovered. While a ninth planet had been theorized for a long time, the actual discovery came in 1930, making Pluto a planet for less than a 100 years. (20 of which were during the period that Pluto was within Neptune’s orbit.)
Keep reading
If anyone’s looking for a longer explanation, I’d recommend How I Killed Pluto (And Why It Had It Coming) by Mike Brown, who was on the team that discovered Eris and Sedna (both pictured in one of the maps below the cut). I read it a few weeks ago and found it pretty enjoyable–the science is easy to understand, and inter-spaced with the memoir enough that it’s not overwhelming or textbook-y.
i’m now at peace with pluto not being a planet
