Why Pluto is Not a Planet

This is a video explainer that describes why Pluto is no longer a planet. It talks about the history of Pluto and its discovery, and then the discovery of Eris, which is larger than Pluto. Now you can learn the official rules for planethood. Created by Christian Ready for Universe Today

[HTakara]

Pluto will forever be a planet in my heart </3

[frasercain]

No, their orbits don't actually intersect because Pluto's orbit is highly inclined.

[SabbyNeko]

I got half way through that Rick and Morty episode before I had to Google for an actual answer. Seems this is the only resource out there that actually explains in laymans terms why Pluto no longer meets the definition of a planet, rather than reporting on the controversy surrounding it.

Thanks for that.

[frasercain]

Dwarf planets can have Moons. Eris has at least 1 moon as well.

[laurele]

Each class of planets is different from one another. Putting the eight largest together in one category and then saying Pluto is different results from cherry picking one set of characteristics over others. The point of the geophysical planet definition is to have "planet" as a broad category with multiple subcategories to designate the many different types of planets.

[laurele]

Eris was initially thought to be bigger than Pluto but in Nov. 2010, more accurate measurement showed it is slightly smaller though more massive. But Eris is certainly rounded by its own gravity and therefore a planet.

[richo]

"Pluto was my(and still is) favorite planet"
That's cool - it is still the same object - and it can stay a favorite - it hasn't changed.
Its like Ceres, Pallas and Vesta - they were all called Planets when they were discovered - now we call them asteroids and Dwarf Planets.
If we insisted on Pluto staying a Planet - then we wouldn't have 9 planets we would have >70, 000.
Easier to have 8 planets and lots of Dwarf planets, Comets and asteroids. The decision was the most sensible one available.

[frasercain]

The Voyagers didn't pass near Pluto when they left the Solar System. But New Horizons is headed straight for it, and will take pictures in 2015.

[lilgossgirl]

Thank you so much for this video. I've always wondered why Pluto was now a dwarf planet and you explain it wonderfully :)

[frasercain]

@christianready Right. Any two objects orbiting one another will have a barycenter somewhere, but Pluto and Charon orbit a location that's above Pluto's surface. For a while astronomers proposed that it made Pluto a binary planet.

[LaunchPadAstronomy]

You could even sub-classify the giants into gas giants (Jupiter & Saturn) and Ice Giants (Uranus & Neptune)

[rubyatneta]

i came here to do homework for science class. pretty helpful video! it also helped my cousin know why Pluto is no longer a planet.

[randombobandfriends]

This really helped me out with my homework - Thanks!

[laurele]

Yes, they are, according to the geophysical planet definition, because they orbit a star and are rounded by their own gravity (a state known as hydrostatic equilibrium).

[laurele]

Agreed. I expect we will need to create additional subclasses for exoplanets we find that do not fit into any of the existing planet categories.

[woodfur]

I always wondered what the exact definition of a planet was and why Pluto wasn't one; now I know. Thank you.

[ulfberht]

From what I’ve read, Pluto is being promoted as a planet again. I think it was because of how problematic the whole rebranding will be for textbooks, lectures, history etc., it’ll total chaos. Plus, we’ve known Pluto as a planet for so long, almost 80 years in fact, and now it’s going to be demoted. Again, that causes major problems. It’s all complicated but I’m glad they’re making Pluto a planet again. It’s good to have some exceptions in life. After all, when has science ever been consistent itself?

[frasercain]

Well, it was scientists that discovered Pluto in the first place. And now they've discovered all these new objects too.

[Stormprobe]

So much Pluto hatred. But when we got there, there was a giant heart staring at us. So perfect.

[jaytea]

Excellent video and narration Fraser! Nice graphics to facetime ratio!