Right, so if you’re like me, then you had learned in school that there were 9 planets .
Viz. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus (stop laughing) , Neptune and Pluto.
But since, 2006 , this list has changed, the IAU no longer considers pluto as a planet?
BUT WHY? HE WAS MY FAVORITE!
So, I was the only one who thought this guy lived in space ?
I know right? Why would anyone do that? He was so cute !
Okay I’ll grow back up now
Okay but seriously, why did they do this? And why is Pluto not a planet anymore?
What the hell is a planet anyway?
Well, that is the tricky part. Because after 2006 , the IAU changed the definition of the word ‘planet’ .
Okay, so to understand the curious case of pluto, let us learn what our little solar system is made of .
So lets see .. there is a big hot thing in the center around which everything revolves.
Then, the closest to that is mercury, followed by venus, then us, then mars.
Between mars and Jupiter there is an asteroid belt which consists of huge rocks floating through space
Then Jupiter, Saturn, Uranus
Right next to pluto is the kuiper belt, which is very much like the asteroid belt but much much larger and with larger rocks.
Right ,so lets go back to the main topic of why Pluto isn’t a planet anymore.
Well, after 2006 , the IAU changed the definition of a planet as follows
A planet is a
1) a body which revolves around its neighboring star (check)
2) is a sphere by its own gravity ( wooohoo we are on a roll)
3) and ‘clears its neighborhood’ (aw, dang.)
So, pluto fails to meet the 3rd criteria .
But what does it mean?
It means that it’s gravity must be the dominant one in its neighborhood.
Meaning that it must either eat or fling away the other neighboring things that are flying around it .
So turns out, Pluto is incapable of doing so .
Some objects in the Kuiper belt are more dominant than Pluto. And hence, it fails to be recognized as a planet today.
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Image sources: https://www2.bc.edu/alaina-beyar/images/pluto.jpg