Planet or Space Debris?

I keep hearing Pluto referred to as a planet when the evidence certainly points to it being a Kuiper Belt object(along with it’s Charon and Triton) trapped in orbit around the sun. Most people I talk to say it should remain a planet. I say no.

  1. Should we demote Pluto?

  2. How should we define planet? (The Webster’s definition is to vague)

Tougher question than it sounds. E.g., did you realize that by some definitions Jupiter is a star? (And I’m talking astrophysics, not “well, it’s a point of light, so…”) Under gravational contraction and possibly radioactives in its core, Jupiter emits at a temperature 100 K what it would be at from insolation alone.

My categories:
Star: Mass of hydrogen, helium, and admixtures of heavier elements powered by nuclear fusion of some sort, with at least some visible light emitted (not reflected). Includes as special cases white dwarfs and neutron stars, which technically don’t meet first half of definition.
Brown dwarf: Composed as with star but does not undergo nuclear fusion. Radiates in infrared from gravitation and radioactives. Shines if at all by reflected light.
Giant planet: Composed as with star but does not radiate measurably. Shines as with brown dwarf.
Terrestrial planet: Composed of rock and/or metal. May also have atmosphere and perhaps hydrosphere if heavy enough. Shines as with brown dwarf. Minimum size: over 1,000 km radius.
Asteroid: Resembles terrestrial planet (but without atmosphere). Maximum size: under 1,000 km radius.
Iceball: Composed of frozen volatiles, possibly with rock/metal admixture.

Under this definition, the Solar System has:
1 star, 1 brown dwarf, 3 giant planets, 4
terrestrial planets, ~1,000 asteroids, and ~100 known iceballs.

Well, it’s smaller than some moons: Strike one.
It has a very elliptical comet-like orbit: Strike two.
Curve ball coming: It has it’s own satellite.

Who’s going to make the call? It was dubbed a planet when Tombaugh found it in the '30s.
Rightly or wrongly, I don’t think anyone’s going to bother demoting this little snowball. And if so, will anyone care?

If you’re hot, that’s good.
If you’re cool, that’s good.

I don’t get it.

Triton? I thought that was moon of one of the Jovian planets.

Have you heard that there is growing evidence of a tenth planet? Two groups of scientists, working independently, have reached the same conclusion, estimating it to be of at least multiple-Jupiters in mass, and located around 3 trillion miles from the sun (a considerable portion of a light year, anyway). I’ll have to break away and repost.

What some people have to say:

Sake, sorry, couldn’t find it right away and the day’s over. I will try again tomorrow, if you’re interested. Also, an asteroid has recently been discovered that has its own satellite body. Unfortunately, that’s also a link I don’t have time to provide now . . .

Cecil on the alleged 10th planet.

Livin’ on Tums, Vitamin E and Rogaine

There has been another object detected out past the orbit of Pluto. (Just this decade, as a matter of fact.) Problem is, it’s even smaller than Pluto, and has an even more eccentric orbit.

This object was deemed too small to be a planet. It’s just a somewhat-close-orbiting Kuiper belt object. And, sorry, I don’t remember the exact year of the discovery or the name given to the object.

Quick-N-Dirty Aviation: Trading altitude for airspeed since 1992.

BTW, I think you meant “Chiron,” not “Triton,” the Neptunian satellite–or is it also considered a KBO?

Simply having a satellite does not prove “planet-ness”. I’ve read of at least one large asteroid which is orbited by another, much smaller asteroid. The name of the object escapes me at the moment (because of my weak gravitational pull, ha!), but I’ll look for a cite when I get home.

Laugh hard; it’s a long way to the bank.

Mjollnir: Triton it Neptune’s largest moon, of the same stock as Pluto, Charon, and hundreds of other pieces of debris.

PolyCarp: I like your classifications. Two observations though. It seems you are counting Mercury as a terrestial planet, when it has a negligible atmosphere. I also think formation should have something to do with the definitions of stellar objects (e.g., Theoreticlly we could terraform an asteroid, suddenly promoting it to a planet).

There is a recent
report which describes a Kuiper belt object which is easily within the definition of planet, aside from its location.



Wrong article. Sigh.

Search in progress, I will try to post the new one when I find it.



Sake: Personally, I wouldnt say that Mars’ atmosphere is that negligible since there are cloud formations (even a hurricane like formation in one photograph), as well as clouds that form off of the tops of the volvanoes. Though they are often very thin and not of much mass, but clouds none the less.

Oh, and the asteroid with a moon is called “Eugenia”. Go here to read about it: Moon Spotted Orbiting Asteroid

‘The beginning calls for courage; the end demands care’

Aiyaa! Ugh, I made a BIG mistake in my first post here, I seriously forgot that Sake Samurai was talking about Mars. I submitted my post and saw that it was Mercury that was being discussed! Horror! This is the last time I post here at 3:50 AM!!! Sorry Sake Samurai! room spinning, odd things appearing before my eyes 'scuse me while I go to bed!

‘The beginning calls for courage; the end demands care’

OK. Chiron is another mysterious object that might possibly be a KBO.

Sake: Agreed that Mercury has no atmosphere (other than when the lead vaporizes ;)), but if you check my definitions, I had atmosphere as an extra-cost option, not standard equipment. If you want atmosphere to come with the purchase price, check out our special on giant planets…


I am really sure I did not make this up, but I cannot find the article again. So, here is my best recollection.

Recently, observations were reported of an object in the remote regions of the solar system which is larger than Jupiter, although still not of stellar size. While further from the Sun than any other observed object included in the “Solar System,” it is on or near the Ecliptic, and might well be a planetary object.

I do not expect anyone to take my word for this, of course, but I hoped that someone else here might have read something about it. I seem to recall it being reported fairly recently, within the last month or two, which would probably place the actual observations some time in the last year.


Here is the BBCNews web site page on the object that is claimed by two separate teams to exist beyond Pluto. Each team reached its conclusions by studying the orbital motions of several Oort cloud comets that had come through the solar system and concluded that their orbits had to have been perturbed by the supposed object.

Interestingly, I read in USA Today that the English astronomer who is making his claim in the Monthly Notices, Dr. John Murray, had his findings rejected by some other publications of ‘higher’ standing. However, there was no such information regarding the American professor publishing in Icarus.

As for whether Pluto is a ‘planet’ or not, define ‘planet’ and then apply the definition… :wink:

The “discovery” is like the “discovery” of extrasolar planets that has been reported on at length over the past couple of years. In both cases,excellent indirect evidence points to the probability of such an object(s). But there is no conclusive, observed proof of its/their existence.