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

• Category

  Science & Technology

[ArbyBrentJ]

Isn't it possible for Neptune & Pluto to collide? Their orbits are on different planes, but Pluto does come inside Neptune's orbit.

[Fraser Cain]

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

[Johndric Valdez]

There is a lot of misconceptions regarding this. It's not true that Pluto is no longer a planet. It's still a planet, but a dwarf planet. It orbits the sun, so it's a planet. It became a dwarf planet because it's much smaller than the moon. But it's still a planet.

[Laurel Kornfeld]

There are three, not two, classes of planets: four terrestrials, four gas giants, and six and counting dwarf planets.

[Laurel Kornfeld]

Pluto is not a "dirty snowball," a description used for comments. It is estimated to be 70% rock, and it is geologically differentiated into core, mantle, and crust just like Earth is. That does not equal crumbly rock. Any planet brought close enough to its parent star would develop a tail. Mercury has a tail, as do some very large exoplanets orbiting very close to their stars. It turns out this is very normal behavior for planets in close orbits.

[virumoz]

If you go by composition, you’ll arrive at the distinction that Neil deGrasse Tyson, for example, usually makes:

the innermost four rocky planets;

the gas giants which are the next four;

finally, dirty snowballs with crumbly rocks caked in.

So you see, your composition criterium lets you arrive at just that picture. After all, if Pluto was as close to the sun as Earth is, Pluto would develop a comet tail. »That’s not a proper behaviour for a planet!« (Tyson -:)

[James Haney]

Really picky about that debris-clearing stipulation.

[Laurel Kornfeld]

It doesn't make sense and is inconsistent with the use of the word dwarf in astronomy. Dwarf stars are still stars, and dwarf galaxies are still galaxies. Dwarf planets are compositionally just smaller versions of the larger planets.

[wasup dude]

pluto is always a bit piece of rock so much as other big bunch of rocks.It is or it is nok the planet definition says planet is an astronomical object orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity. lack of right definition cause the discovery of a new planet(?) ops rock!! :)

[MRconfusedboy]

pluto is part of the solar system, i dont agree with that bs :D i love you pluto