03-22-2004, 06:57 AM
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Developer & Designer, News Editor Emeritus
Join Date: Aug 2006
Posts: 12,959
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Sedna - the 10th planet or not?
In case you've been 'out of this world', scientists discovered a supposed 10th planetary body about a week ago, which they've called Sedna.
It's three times further from Earth than Pluto is.
The question I'm asking is - do you think Sedna is a planet, or just some asteroid floating around?
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03-22-2004, 12:55 PM
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Intellectual
Join Date: Dec 2003
Posts: 217
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Jupiter is a planet. Saturn is a planet. Sedna is not a planet. I don't think Pluto is either but because it has been considered a planet for so long it's only fair that it retains it's planetary status.
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03-22-2004, 01:25 PM
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Ponderer
Join Date: Jan 2004
Posts: 95
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Isn't there a minimum size to be designated a planet? Calculations so far suggest that Sedna is, at most, 1,000 miles in diameter. That's half the diameter of Pluto.
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03-22-2004, 01:48 PM
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Philosopher
Join Date: Aug 2006
Posts: 541
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Based on the dictionary definitions of a Planet SEDNA could be either one that is why astronomers are going to meet to nail down the definition of a planet and decide whether Senda is the 10th planet or a permantly orbiting asteroid.
IMHO it is a planet albeit a very small one...
plan�et ( P ) Pronunciation Key (plnt)
n. - A nonluminous celestial body larger than an asteroid or comet, illuminated by light from a star, such as the sun, around which it revolves. In the solar system there are nine known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
- One of the seven celestial bodies, Mercury, Venus, the moon, the sun, Mars, Jupiter, and Saturn, visible to the naked eye and thought by ancient astronomers to revolve in the heavens about a fixed Earth and among fixed stars.
- One of the seven revolving astrological celestial bodies that in conjunction with the stars are believed to influence human affairs and personalities.
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Middle English, from Old French planete, from Late Latin planta, from Greek plants, variant of plans, plant-, from plansthai, to wander. See pel-2 in Indo-European Roots.
planet
\Plan"et\, n. [OE. planete, F. plan[`e]te, L. planeta, fr. Gr. ?, and ? a planet; prop. wandering, fr. ? to wander, fr. ? a wandering.]
1. (Astron.) A celestial body which revolves about the sun in an orbit of a moderate degree of eccentricity. It is distinguished from a comet by the absence of a coma, and by having a less eccentric orbit. See Solar system.
Note: The term planet was first used to distinguish those stars which have an apparent motion through the constellations from the fixed stars, which retain their relative places unchanged. The inferior planets are Mercury and Venus, which are nearer to the sun than is the earth; the superior planets are Mars, the asteroids, Jupiter, Saturn, Uranus, and Neptune, which are farther from the sun than is the earth. Primary planets are those which revolve about the sun; secondary planets, or moons, are those which revolve around the primary planets as satellites, and at the same time revolve with them about the sun.
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03-22-2004, 03:38 PM
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Thinker
Join Date: Aug 2006
Posts: 439
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I figure, if it has enough mass to create enough gravity to make itself round, as opposed to some irregular lumpy shape, and has a nice semi round orbit, why not call it a planet.
There is also some kind of equation that you can use to figure out where planets "should" be. All the existing planets, except pluto, but including the asteroid belt (which could have been a planet at one time) work with this equation. I wonder if Sedna does.
Robb
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03-22-2004, 05:44 PM
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Moderator Emeritus
Join Date: Aug 2006
Posts: 1,998
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I'm not a scientist by any stretch, but to me a planet maintains an orbit around the sun, just as a moon orbits a planet. I'm probably over simplifying it, but that's what qualifies to me.
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03-22-2004, 05:56 PM
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Thinker
Join Date: Aug 2006
Posts: 439
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Yes, but comets orbit the sun, as does the asteroid belt. But they're not planets. I think it's all about the size of the thing and definitely some politics going on. "What? ten planets? no way, there have always been nine!"
Robb
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03-22-2004, 06:07 PM
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Moderator Emeritus
Join Date: Aug 2006
Posts: 1,998
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Good points. Like I said, I figured I was over simplifying it. 
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03-22-2004, 06:24 PM
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Magi
Join Date: Feb 2004
Posts: 2,186
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I think the main determining factor will probably be whether it's classified as a "Kuiper Belt Object". This is a ring of icy objects that orbit the sun beyond Neptune.
There are some who think that Pluto is a Kuiper Belt Object, which is why we've had the debates in recent years about whether Pluto is a planet.
In my opinion, it's a planet if it's a) at least Pluto size or larger, and in a fairly stable orbit around the sun, or b) got a satellite. While Pluto has a highly eccentric orbit (it's sometimes inside the orbit of Neptune), it does have a satellite. If Sedna has an orbit like Pluto's, and it does NOT have a satellite, I don't think it should be classified as a planet.
This was also debated a few years ago when Quaoar was discovered.
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03-22-2004, 07:11 PM
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5000+ Posts? I Should OWN This Site!
Join Date: Jul 2003
Posts: 5,133
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I think it's all about publishers wanting to make new textbooks and schools not wanting to have to buy them... 
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