Definition of a planet

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25-08-2006, 10:09 PM
Kardan

Definition of a planet

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.

http://i70.photobucket.com/albums/i9...bo/planets.png
25-08-2006, 10:29 PM
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.

Quote:

Originally Posted by Wikipedia

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.
25-08-2006, 10:31 PM
RedStratocas

Its all confusing and everyone wants to be so technical about it. It is kinda weird how sometimes pluto isnt the farthest planet.
25-08-2006, 10:45 PM
Drewar

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

Quote:

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?
25-08-2006, 10:59 PM
Jesus-Egg

Quote:

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
25-08-2006, 11:01 PM
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.
26-08-2006, 12:20 AM
RedStratocas

Quote:

Originally Posted by Drewar

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.
26-08-2006, 12:21 AM
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.
26-08-2006, 12:23 AM
RedStratocas

Quote:

Originally Posted by Night

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.
26-08-2006, 12:25 AM
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.
26-08-2006, 12:38 AM
RedStratocas

Quote:

Originally Posted by 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.

Yes, it is possible, but is said to not happen for another thousands of years. And they arent sure what would happen, because neptune is a gas planet. (a planet thats basically gas, like a cloud). So they arent sure if pluto would just pass right through, or if it would mess up the shape or what.
26-08-2006, 12:59 AM
FlyingJesus

Neptune would probably just dissolve Pluto or something.. that would be quite a laugh.
26-08-2006, 03:56 AM
Herman

Quote:

Originally Posted by FlyingJesus

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.

Haha, that would be interesting to see. But anyway, all this planet stuff gives me a headache. I say just leave the solar system as it is, 9 planets. And forget about the other stuff they found, like Xena or whatever. :) Kidding.
26-08-2006, 08:29 AM
FrozenWhisper

Quote:

Originally Posted by Herman

Haha, that would be interesting to see. But anyway, all this planet stuff gives me a headache. I say just leave the solar system as it is, 9 planets. And forget about the other stuff they found, like Xena or whatever. :) Kidding.

Imo, there will stil always be 9 planets. None of this "dwarf planet" stuff.
26-08-2006, 11:14 AM
beth

Quote:

Originally Posted by 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.

thats's what i was thinking, i mean my science exam is next may.. are we seriously meant to learn this whole new complicated definition in that time? cus i know i won't remember it, rofl.
26-08-2006, 07:33 PM
FlyingJesus

I've never had a science question to do with the planets, ever. And I've finished school.
26-08-2006, 07:58 PM
beth

Quote:

Originally Posted by FlyingJesus

I've never had a science question to do with the planets, ever. And I've finished school.

i had a few in my uh year 9 SATs. i think. or it could have been year 6.
26-08-2006, 08:07 PM
Mentor

Quote:

Originally Posted by RedStratocas

Yes, it is possible, but is said to not happen for another thousands of years. And they arent sure what would happen, because neptune is a gas planet. (a planet thats basically gas, like a cloud). So they arent sure if pluto would just pass right through, or if it would mess up the shape or what.

actualy chances are very unlikly they ever will, becuse of there orbit timeing they never come even remotly close to each other, earth is closer to the sun that pluto ever comes to neptune