Why Pluto Isn’t a Planet

From its discovery in 1930 to its demotion to dwarf planet status in 2006, Pluto was the ninth planet in our solar system.  To many of us, who grew up with nine planets, the news that we lost Pluto was almost heartbreaking.  To this day, there are those who refuse to accept the decision that the International Astronomical Union (IAU) had made and continue to call Pluto a planet.

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But was Pluto’s demotion a stupid decision?  Why was it demoted in the first place?  Well, there are a slew of reasons, so let’s go through them:

(1)  Pluto is smaller than the Moon, in every way.

Pluto’s diameter is only 70% of the Moon’s diameter, giving Pluto only about 34% of the Moon’s volume and only 0.59% of the Earth’s volume.  You could fit almost 170 Plutos inside Earth.  Pluto has 18% the mass of the Moon or 0.2% the mass of the Earth.  Pluto’s surface area is 3.3% the surface area of the Earth, and if you were to ‘flatten’ Pluto out, it would roughly cover an area the size of Russia.

pluto_earth_charon_compared_800

 

(2)  Pluto has, like, a gazillion brothers and sisters, and it’s not the biggest.

At the time of its discovery, Astronomers thought that Pluto was the biggest thing past Neptune, so they thought it was a safe assumption to call it a planet.  However, astronomical equipment has improved a lot since 1930, and astronomers were able to find that there are an estimated 70,000 objects in the Kuiper Belt (the belt of objects on the edge of our solar system) that have the same composition as Pluto.  Most of them are smaller than Pluto; however, there a few that are roughly the same size, and one so far that is actually bigger than Pluto—Eris.

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(3)  It doesn’t dominate its orbit.

Planets dominate their obits, meaning that if smaller objects were to get near its orbit, it would have influence over them and either consume them or eject them into deep space.  Pluto doesn’t do that.  In fact, it has only 0.07 times the mass of the other objects in its orbit.  It’s not the big dog, it’s the Chihuahua.

Due to these reasons, especially number 3, the IAU decided that it wasn’t okay to call Pluto a planet anymore.  After all, if they did, does that mean that Eris is a planet?  Or how about the other similar objects in the Kuiper belt, are they planets, too?  Instead of having a solar system with a ton of planets, we decided to have one with just eight.

I would say that these reasons are good enough to say that the IAU was not stupid to demote Pluto, and that it is for the best that they did.

Now that you know the details of Pluto’s sob story, what do you think?  Should we have kept Pluto?  Even if you think that we should have, the IAU’s decision is final.  Pluto is never coming back as a planet, so there is only one thing we can say:  goodbye.  Revolve in peace, Pluto, revolve in peace.

Links:

http://www.universetoday.com/39565/how-big-is-pluto/

http://www.universetoday.com/13573/why-pluto-is-no-longer-a-planet/