Definition of a planet

[Kardan]

Here's the scientific explanation of what a planet is:

(a) in orbit around a star or stellar remnants
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape
(c) is not massive enough to initiate thermonuclear fusion of deuterium in its core
(d) has cleared the neighbourhood around its orbit.

For information of what "clearing the neighbourhood" means read this article:

http://en.wikipedia.org/wiki/Clear_the_neighbourhood

And this is our solar system and beyond.

Read from top left box and continue clockwise.

[Jesus-Egg]

I don't like this definition. Well, part a, b and c are fine, but i don't like this "clearing the neighbourhood" stuff. Neptune passes across the orbit Pluto, therefore Neptune hasn't cleared its neightbourhood of all objects. So, technically, Neptune should be a dwarf planet. If they're going to have an official definition of a planet, they need one that doesn't have a huge flaw in it.

Dr. Alan Stern, who leads the NASA New Horizons mission to Pluto, contends that Earth, Mars, Jupiter and Neptune have also not fully cleared their orbital zones, which would technically make them qualify as dwarf planets. Earth orbits with 10,000 near-Earth asteroids. Jupiter, meanwhile, is accompanied by 100,000 Trojan asteroids on its orbital path. "If Neptune had cleared its zone, Pluto wouldn't be there," he added.

[RedStratocas]

Its all confusing and everyone wants to be so technical about it. It is kinda weird how sometimes pluto isnt the farthest planet.

[Drewar]

I almost wanted to -rep you for making my head hurt.

has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium

I didn't though :p Considering I want to be a doctor I guess I'll have to start being, how do you say, ummmmmm, "smart".

Anyway yeah, I agree with RedStratocas (as always), it's weird how sometimes Pluto/Neptune trade spots or whatever.

Guess Neptune wins farthest now eh?

[Jesus-Egg]

has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium

Basically, all that means is that it is big enough for it's gravity to pull it into a round shape

[Victimized]

What happens if we get a question about this in GCSE's?


Coz i doubt they'll have time to update everything we know about the solar system in like 9 months.

[RedStratocas]

Anyway yeah, I agree with RedStratocas (as always), it's weird how sometimes Pluto/Neptune trade spots or whatever.

Guess Neptune wins farthest now eh?

Well not really, pluto is extremely far from the sun at times. And it isnt directly orbiting around it. Like the sun is almost perfectly in the center of earth's orbit, but not of pluto's.

[Sarah.]

all this stuff about planets confuses me. why do these people have the power to decide what's a planet and what's a "dwarf planet"? all it does is confuse everybody and soon it'll probably be changed again.

[RedStratocas]

all this stuff about planets confuses me. why do these people have the power to decide what's a planet and what's a "dwarf planet"? all it does is confuse everybody and soon it'll probably be changed again.

Thats really the point.

[FlyingJesus]

Don't suppose anyone knows why the orbits of some planets don't feature the Sun in the absolute centre? Seems strange that the point of high gravity that causes the planets to go round and round and round and round and round doesn't cause them to go round and round and round and round and round at the same distance from it at all times.

Also, is it possible for Pluto and Neptune to collide? I'm sure the odds of it happening are pretty slim but it must be a chance if their orbits intercept each other.