Freethought & Rationalism Archive

Abacus · 10-08-2002, 02:55 PM

Quote:

Originally posted by Liquidrage:
<strong>To me it's a planet.

What makes a planet/moon round while most asteroids are not? Is it not the gravitational force pulling the surface inwards and thus creating the round shape?

And if an object has enough mass to have this process occur (the rounding, all objects obviously have the process) and it is orbiting a star directly then to me that is a planet.</strong>

So, should the asteroid <a href="http://www.sudekumplanetarium.com/features/2001/01-09ceres.shtml" target="_blank">Ceres</a> located in the asteroid belt be considered a planet? It is spherical as well.

[ October 08, 2002: Message edited by: Abacus ]

[ October 08, 2002: Message edited by: Abacus ]</p>

Liquidrage · 10-08-2002, 03:09 PM

So, should the asteroid <a href="http://www.sudekumplanetarium.com/features/2001/01-09ceres.shtml" target="_blank">Ceres</a> located in the asteroid belt be considered a planet? It is spherical as well.

Why not? Because there are are lots of other objects in the same orbital plane that are much smaller that don't display the same gravitational crushing? There might even be a few more in the asteroid belt that would satisfy my definition of planet.
If it is large enough to experience gravitational crushing to the extent of making an obvious sphere and it orbits a star then to me that is a planet.

Autonemesis · 10-08-2002, 03:32 PM

My take on the planet/asteroid dilemma is that an object is not a planet unless:

1) It is large enough to assume a spherical shape
2) It does not closely share similar orbital characteristics with many other similar and/or related objects
3) Stable orbit

What's so wonderful about my definition? All the objects we think of as planets remain planets, and none of the objects we think of as not-planets become planets under this definition. I think it might need a little refinement to make it more specific, but the general principle that a planet is a standout or exception among solar system objects is central to my idea, and I think it is a good one.

All the objects we consider planets are unusual and rare, when compared to the totality of objects in the solar system. It's possible Pluto might be demoted to a Kuiper belt object under my definition, if "similar orbit" and "closely related objects" are defined just so, but I don't mind that.

I think Pluto IS an example of a large Kuiper belt object, but sometime in the past, it was thrown into its unusual orbit, perhaps by interaction with Neptune, or a nudge from a passing star. My idea would be discounted if other Kuiper belt objects are discovered in eccentric, highly inclined orbits similar to Pluto. But then Pluto would no longer be a planet, since would share orbital characteristics with other similar or related objects.

Bottom line: get it over with, the 9th planet is really 0 Pluto (followed by 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, etc.).

[ October 08, 2002: Message edited by: Kind Bud ]</p>

Hypernovean · 10-09-2002, 10:18 PM

Why not just call Pluto, Quaoar, and any other similar objects discovered in the future, "planetoids"? Not quite planets, but also not quite asteroids/comets/et cetera. The name "ice dwarf", I think fits nicely; and if it isn't made purely from ice, call it a "dwarf planet", or something similar.
In my opinion, not evry spherical object should be clumped under the title "planet". If it's small, and/or shares its orbital area with a lot of other objects, just call it a planetoid/planetissimal/dwarf planet/whatever. Just not a planet!

Shadowy Man · 10-10-2002, 06:14 AM

I have yet to see where Pluto and Quaoar fall on the size distribution function of Kuiper Belt objects, but I don't see any reason not to call it a Kuiper Belt object.

Naming is just semantic convention anyway, so in the end it really doesn't matter.

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10-08-2002, 03:09 PM	#12
Liquidrage Veteran Member Join Date: Dec 2001 Location: Tallahassee Posts: 1,301	So, should the asteroid <a href="http://www.sudekumplanetarium.com/features/2001/01-09ceres.shtml" target="_blank">Ceres</a> located in the asteroid belt be considered a planet? It is spherical as well. Why not? Because there are are lots of other objects in the same orbital plane that are much smaller that don't display the same gravitational crushing? There might even be a few more in the asteroid belt that would satisfy my definition of planet. If it is large enough to experience gravitational crushing to the extent of making an obvious sphere and it orbits a star then to me that is a planet.

10-08-2002, 03:32 PM	#13
Autonemesis Contributor Join Date: Feb 2002 Location: I've left FRDB for good, due to new WI&P policy Posts: 12,048	My take on the planet/asteroid dilemma is that an object is not a planet unless: 1) It is large enough to assume a spherical shape 2) It does not closely share similar orbital characteristics with many other similar and/or related objects 3) Stable orbit What's so wonderful about my definition? All the objects we think of as planets remain planets, and none of the objects we think of as not-planets become planets under this definition. I think it might need a little refinement to make it more specific, but the general principle that a planet is a standout or exception among solar system objects is central to my idea, and I think it is a good one. All the objects we consider planets are unusual and rare, when compared to the totality of objects in the solar system. It's possible Pluto might be demoted to a Kuiper belt object under my definition, if "similar orbit" and "closely related objects" are defined just so, but I don't mind that. I think Pluto IS an example of a large Kuiper belt object, but sometime in the past, it was thrown into its unusual orbit, perhaps by interaction with Neptune, or a nudge from a passing star. My idea would be discounted if other Kuiper belt objects are discovered in eccentric, highly inclined orbits similar to Pluto. But then Pluto would no longer be a planet, since would share orbital characteristics with other similar or related objects. Bottom line: get it over with, the 9th planet is really 0 Pluto (followed by 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, etc.). [ October 08, 2002: Message edited by: Kind Bud ]</p>

10-09-2002, 10:18 PM	#14
Hypernovean Junior Member Join Date: Oct 2002 Location: - Posts: 67	Why not just call Pluto, Quaoar, and any other similar objects discovered in the future, "planetoids"? Not quite planets, but also not quite asteroids/comets/et cetera. The name "ice dwarf", I think fits nicely; and if it isn't made purely from ice, call it a "dwarf planet", or something similar. In my opinion, not evry spherical object should be clumped under the title "planet". If it's small, and/or shares its orbital area with a lot of other objects, just call it a planetoid/planetissimal/dwarf planet/whatever. Just not a planet!

10-10-2002, 06:14 AM	#15
Shadowy Man Veteran Member Join Date: Jun 2002 Location: A Shadowy Planet Posts: 7,585	I have yet to see where Pluto and Quaoar fall on the size distribution function of Kuiper Belt objects, but I don't see any reason not to call it a Kuiper Belt object. Naming is just semantic convention anyway, so in the end it really doesn't matter.

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