A Conversation for Ask h2g2
How should we define "planet"?
Lemon Blossom (aka Athena Albatross) Started conversation Mar 21, 2004
How should we define "planet"?
I suggest that it should be an object orbiting a star (or co-orbiting a star with an object no more than 100 times its mass) massive enough that its shape is determined solely by gravity and rotation.
This definition gives the solar system at least 16 planets:
1.) Mercury
2.) Venus
3a.) Earth
3b.) Luna
4.) Mars
5.) Ceres
6.) Jupiter
7.) Saturn
8.) Uranus
9.) Neptune
10.) Ixion
11a.) Pluto
11b.) Charon
12.) Varuna
13.) Quaoar
14.) Sedna
Planets 1-5 are terrestrial, planets 6-9 are jovian, planets 10-14 are KBOs (I propose the name plutonian to describe them).
Disagree? Agree? Alternate definitions?
How should we define "planet"?
DA ; Simply Vicky: Don't get pithy with me! Posted Mar 22, 2004
Your definition makes sense to me, Lemon...
How should we define "planet"?
Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! Posted Mar 22, 2004
I think it should be by "roundness" and a good tea shop!
How should we define "planet"?
Potholer Posted Mar 22, 2004
Not sure I'm adding much here, but anyway...
Is there any accepted definition (apart from a 100:1 mass ratio) for distinguishing between 'orbiting' and 'co-orbiting'.
I seem to remember some distinction betwen 'planet' and 'satellite' that was based on the centre of rotation of the two bodies, which I *think* would make Luna a satellite if the centre of rotation is within the Earth.
How should we define "planet"?
Lemon Blossom (aka Athena Albatross) Posted Mar 22, 2004
"I seem to remember some distinction betwen 'planet' and 'satellite' that was based on the centre of rotation of the two bodies, which I *think* would make Luna a satellite if the centre of rotation is within the Earth."
I came up with the 1:100 one myself. I've never heard it mentionedd anywhere.
As for the center of rotation, I'm pretty sure I've read that it is outside of the Earth.
As for the earlier post someone made, the current definition for planets in our solar system is anything on the list of nine things the IAU calls planets. No general rule exists. For extrasolar planets, it is anything orbiting as star too light to fuse deuterium.
How should we define "planet"?
Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! Posted Mar 22, 2004
I'm still thinking "roundness" is pritty good way of defining a "planet" as i hav'ent seen anything here which even comes close to a logical argument!
How should we define "planet"?
A Super Furry Animal Posted Mar 22, 2004
>> As for the center of rotation, I'm pretty sure I've read that it is outside of the Earth. <<
All the evidence suggests otherwise, LB. Care to back that one up?
RF
How should we define "planet"?
MMF - Keeper of Mustelids, with added P.M.A., is now in a relationship. Posted Mar 22, 2004
I was taught that a Planet is an object that had an orbit (regular or otherwise) around a star-like object, and that a star was an object that released energy. Thus 'object' 10, by definition, is a planet. However some astronomers claim that Pluto, Mercury and other such objects are purely satellites that have too much mass to be sub-summed by the star, but too little to be planets. They are effectively free-loaders.
How should we define "planet"?
A Super Furry Animal Posted Mar 22, 2004
Don't gas giants emit energy? Admittedly not as much as the sun, but I understand that there is such a thing as Saturn-shine.
RF
How should we define "planet"?
Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! Posted Mar 22, 2004
"Roundness" "roundness" is the way to define planets on h2 today
How should we define "planet"?
A Super Furry Animal Posted Mar 22, 2004
I think "round, and orbiting the sun" is the way. Otherwise the moon becomes a planet.
RF
How should we define "planet"?
A Super Furry Animal Posted Mar 22, 2004
Oh, and one other thought...
Why should we define planets? Is LB planning to take over the Solar System this time?
RF
How should we define "planet"?
Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! Posted Mar 22, 2004
YAY i knew it!
How should we define "planet"?
HonestIago Posted Mar 22, 2004
I think the biggest argument for the moon not being a planet is the fact that it's matter came from the Earth. I can't think of a good argument for Charon not being a planet though
How should we define "planet"?
Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! Posted Mar 22, 2004
i'm off to take the dogs for a walk! TTFN!
How should we define "planet"?
Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! Posted Mar 22, 2004
right i'm back, just taken the dogs out and i've been pondering this unverse shaking poser, as we are the only ones actually living in the unverse that we know of, it really dos'ent matter does it, untill we can check it against someone elses defnition it my not be revelent, we can't even travel to the next planet!
I'm still thinking that "roundness" will be the best way for science to define planets, as its best to keep it simple, because all the best science stuff has really simple definitions, I could be wrong!
How should we define "planet"?
GodBen (The Magical Astronomer) - 00000011 Posted Mar 22, 2004
Pluto's not a planet. Sedna's not a planet.
How should we define "planet"?
A Super Furry Animal Posted Mar 22, 2004
Them's fightin' words, GodBen!
RF
How should we define "planet"?
GodBen (The Magical Astronomer) - 00000011 Posted Mar 22, 2004
No, they're just the reality we'll have to face up to.
Key: Complain about this post
How should we define "planet"?
- 1: Lemon Blossom (aka Athena Albatross) (Mar 21, 2004)
- 2: DA ; Simply Vicky: Don't get pithy with me! (Mar 22, 2004)
- 3: creachy (Mar 22, 2004)
- 4: Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! (Mar 22, 2004)
- 5: Potholer (Mar 22, 2004)
- 6: Lemon Blossom (aka Athena Albatross) (Mar 22, 2004)
- 7: Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! (Mar 22, 2004)
- 8: A Super Furry Animal (Mar 22, 2004)
- 9: MMF - Keeper of Mustelids, with added P.M.A., is now in a relationship. (Mar 22, 2004)
- 10: A Super Furry Animal (Mar 22, 2004)
- 11: Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! (Mar 22, 2004)
- 12: A Super Furry Animal (Mar 22, 2004)
- 13: A Super Furry Animal (Mar 22, 2004)
- 14: Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! (Mar 22, 2004)
- 15: HonestIago (Mar 22, 2004)
- 16: Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! (Mar 22, 2004)
- 17: Jackruss a Grand Master of Tea and Toast, Keeper of the comfy chair, who is spending a year dead for tax reasons! DNA! (Mar 22, 2004)
- 18: GodBen (The Magical Astronomer) - 00000011 (Mar 22, 2004)
- 19: A Super Furry Animal (Mar 22, 2004)
- 20: GodBen (The Magical Astronomer) - 00000011 (Mar 22, 2004)
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