Yes, it wouldn´t be a planet anylonger. Objects with eccentric, secant orbits, are unstable in the long run. Only stable objects would qualify for planethood. If a Jupiter-sized object would throw us out of our stable orbital path, we would start living on a planetoid, in which case we´d better take steps for abandoning it quickly.

No way. Earth sized objects in the Kuiper belt would be planets if they had a stable orbit. Notice that only the gravitational signature is enough to the classification. No assumptions, no arbitrary limits. Domina gravitas ruling.

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Thanks for answering the poll. I think this summarized all the prevailing thoughts on the subject.

I would like to add something I didn't see mentioned. Remember when Titan was called a planet, casually? Its composition and dynamics is what is of interest to the geologist, and what it's orbiting is not a meaningful part of the "terrestrial planet" designation.

We need a word for any astronomical body that is indeed a separate body (it is disjoint from others), not a star or black hole, and implies that it is a place of interest. The meaning of "interesting" is context-dependant, not absolute.

If you want to be absolute, you wind up with overlapping classifications, period.

How many counties are there in the U.S.? Can you name them? There is a big book at the post office, if you really cared. Knowing 50 states is bad enough, and most people who live in one can't enumerate them but can tell you whether a name is or is not a state. Speaking of which, software that processes addresses needs to treat "DC" identically to a state, but it is defined as not being one.

Just as we have a greater awareness of geography that is local to us, we find those planets that are also part of the central disk to be inherently interesting because they are "nearby" and all different.

The least contraversial thing would be to leave the terms "planet", "planetoid", etc. as casual or context-dependant. The IAU has a list of all the individual items. Different people want to group them together in different ways, and each grouping could have a name for the group, standardized to a level appropriate to the range of its audiance.

What do you call a trunkless elephant? The term "trunkless elephant" is indeed the most succienct and immediatly meaningful term, even though "having a trunk" is one of the defining properties of an elephant! We can intuitivly make sence of things even without a strict definition.

Spiders and slugs are not "bugs". So what is the term for a tiny critter that doesn't immediatly appear to be mamalian and is crawling through the kitchen? My wife says, "Eeeek! there's a bug in here!" without stopping to grab a magnifying glass and count its legs. I don't think she would appreciate having to call it a "pest-oid" because taxonomists have a strict definition for everything.

I know better than to call a tiny mullosk a "bug", just as I know better than to call a large plutino a "planet".

So, any word on when the definition will be forthcoming?

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Just one, that I'm aware of. :P

Haha, the way you said that it's almost as if you know what the IAU are going to say... 8-[

Are they? Does, for instance, Pluto not have a 'stable' orbit? Where do you draw the line between a 'stable' and 'unstable' orbit? Somewhere between Mercury's and Pluto's? Somewhere inbetween Pluto's and Sedna's? And what does it take into consideration...eccentricity, inclination or both?

with regards

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I think you think he's saying "countries." he's not; he's saying "counties." very different.

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Hmmm....Counties? I thought that was just English propaganda... :roll:

with regards

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Perhaps he was thinking of the District of Columbia county?

According to this:

http://en.wikipedia.org/wiki/County_%28United_States%29

There are 3086 "counties" (some aren't called that) in the various states or territory.

Here's a map:

http://en.wikipedia.org/wiki/Image:M...y_outlines.png

Now, hopefully, back to astronomy ...

I never knew that, thanks for the pic.

Sorry John Dlugosz...

with regards

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For all of you so hyped on the circular orbit nonsense, you do realize you just demoted over a dozen planets larger than Jupiter found orbiting other stars to "massive concentrations of hydrogen and other gases"?

Jeez. Critical thought, I knew it well, Horatio...

Edit: insufficient caffeine present in bloodstream...

A stable orbit is one that is found to be so. Pluto has a stable orbit because of the high inclination (it always misses Neptune) and because it is in resonance with Neptune. Pluto is a (double) planet in my model.

(*) I don´t know why you put the stable and unstable words between quotes. Stable and unstable are accepted words to refer to orbits, and they have precise meanings; I didn´t invent them.

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Sorry....I don't quite get you...Pluto isn't unstable because it is in resonance with Neptune...and because it has a high inclination? I don't get it. :-?

What are the specifics, you mentioned Pluto is apparently considered a stable planet - what kind of object wouldn't be? It doesn't sound very specific to me.

with regards

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We´re not here to define stability, or orbits.

Pluto´s orbit, though secant and inclined, is stable, and that´s sufficient for my proposed classification.

Comets (orbits) are unstable. They are not planets. Btw, we went through those difinitions on the interesting thread started by Macro Mouse, called "My Idea For Defining a Planet".

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Ok, I'll give that thread a quick browse.

with regards

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OK, I can see you are arguing that we should have thousands of planets...I don't think we should have that many. Thousands or millions of planets is ridiculous, in my opinion. If you're going to be that nondescript, you need to have an extensive classification system to group them all.

I don't see what is wrong with placing Pluto as the arbitrary limit to the size of a planet - provided the object is not big enough to be a brown dwarf, is in orbit around a star[s] and has a stable orbit (which makes plenty of sense now :P).

with regards

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Astronomy is about big numbers. Don´t we already have millions of "asteroids" (planetoids)? Don´t we have millions (billions) of stars and galaxies? Won´t we have thousands (surely millions) of extrasolar planets in the future? When we treat those objects as database records all the problem disappears. After all, only a few objects in each of those categories are significant in day-to-day life, and we´ll always have meaningful names for meaninful objects. The rest can be treated as numbers.

:wink:

Edited

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