After the IAU shares its wisdom, how many official planets will we have in our solar system?

Either 8, or no definition (they have to talk about something on those astro boards after all).

My best guess is 8, though - The Definition will somehow involve near-circularity of orbit and history of formation - thus demoting Pluto/Charon, sadly.

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Non sunt multiplicanda entia praeter necessitatem.

I think that we'll be up to 11 or more.

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Quaeso quousque humi defixa tua mens erit? Nonne aspicis, quae in templa veneris?

Ten, but the number will rise soon.

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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
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I think that Quaoar will be in immediately as well. Not to mention Sedna, Orcus, and the others.

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8 they're clever people, I don't want to have to remember the name of 300 or more planets

I have a feeling they will go 10....but I really don't know what I'd like to happen myself. :-?

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I disagree....such a definition would be ridiculous. Consider we discover a large Earth to Neptune sized with a high eccentricity? And what about exoplanets?

I don't think they will go that far....too many becoming planets at once..

But it was an interesting idea somebody mentioned in a previous post about having:

Rocky inner-planets: Mercury - Mars
Gas planets: Jupiter - Neptune
Kuipter belt planets (or something similar): Pluto and others

It will be very interesting to see what they have to say...

with regards

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Hey, that's no problem, just remember the mnemonic:

Many
Very
Erudite
Men
Just
Shut
Up and
Number the
Planets
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12...300.

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There´s a few thousand planets in this system, according to Argos.

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Forgive my cave habitation, but is the IAU actually going to come up with an official definition that will decide the fate of Pluto? Wow! This is like waiting for the Hutton report.

Where's the cut-off point then? 1000km diameter? There are many 'others' that range in size from UB313 ~2500km down to objects under 500....where do you draw the line?

Good luck, IAU.

=D>

with regards

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Sure hope so...this is the current definition they have:

http://www.iau.org/IAU/FAQ/sedna.html

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Well, only if you are into lists. Pluto will have the same size, shape, orbit, etc., no matter what the decision...

We need a definition that´s suitable for all stars. When you consider that, things like size and shape lose their meaning. Our definition of "planet" must take solely orbital characteristics into account.

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I disagree. What if we discover a solar system that has planets in erratic orbits, not all in the same plane? Large objects... gas giants, even? What would you call them?

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Current theories on planetary formation would rule out this possibility. If components of a planetary system are formed from a primeval disc [i.e. a roughly co-planar collection of objects] of dust an gas a round a star, then one would expect at least one planet (whatever its size and shape) with a stable orbit (whatever the orbit´s shape, except hyperbolic). Erratic objects would be called "planetoids" (whatever their shapes and sizes).

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Well, obviously objects can have erratic orbits (KBO's in our own solar system) but where do you draw the line? If Earth had an eccentric orbit (if say, a large jupiter-sized body was closeby and knocked it out of a 'regular' orbit), would it then be no longer classified as a planet?

And what if we discover another Earth to Neptune sized object beyond the kuiper belt ... is distance going to be an issue as well?

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How about any spherical body with an appreciable (say... Mercury/Pluto) atmosphere orbiting a star is a planet?

Mercury and Pluto would qualify. Titan and Ceres would not.

I guessed 9, partly because of those comments. They could abdicate any responsibility for "planet" at all, and just say that planet is a non-technical term (after all, it was once applied to the sun and moon) like, say, "mile"

I'd say anything that is spherical due to its own gravity.

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I was going to ask which choice in the poll that represents, when I went back to read the poll, and realized that you wouldn't have an answer. However, I think the first choice (0, they refuse to formalize the definition) is misleading--if they don't formalize it, we're stuck with nine (and argumentation )

If we did that Ceres, Quaoar, Sedna, etc all become instant planets.

What if Mercury was even closer to Sun, and it had it's atmosphere totally wiped clean? And we don't know what would happen in other solar systems, about the presence of atmospheres.

I don't think that Ceres is totally circular...but I see your point, I think there would be way too many. :P

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Back in the day when the asteroids were first being discovered, some texts went as far as to say there were twelve planets. Then everyone realized that asteroids don't count and moved on with their lives. I think the same thing will happen now, and we'll end up with eight.
The odd thing is, when this happens after a few generations no one will ever know there were nine planets for awhile, just like only astronomy nerds like me knew at one time there were twelve. Time is an odd creature isn't it?

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I think astronomy is much more prevalent nowdays....and kids at schools who have posters that are more than a couple of years old will still think there are 9 planets. :P

How long were there '12 planets' for?

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Not sure, I just saw a print from an old book that said there were. There was nothing like the IAU back then to set the record straight so it might've just been an author a little behind the times or something.

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Sounds about right to me.

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Quaeso quousque humi defixa tua mens erit? Nonne aspicis, quae in templa veneris?

There's two problems with the "spherical under its own gravity" definition.

1) The composition of the planet (ice vs rock) may make a difference. Ceres, a rocky object, is some 900 km in diameter, yet (as you say) is a bit out of round. Enceladus, an icy moon of Saturn, is only 500 km in diameter, but is round as a cue ball. Rock is stronger than ice, so will support out-of-roundness at larger sizes.

2) There's no natural cutoff where objects below a certain size (even when only comparing objects of like composition) are not round and those above are.


Personally, I think they should use the object's mass to determine whether it's a planet or not. After all, the demarcation between planets and brown dwarfs is usually set by mass. How about 1e22 kg and above for planets?

Is it? I thought it was a little bit out of shape...but I know what you're getting at.

Wouldn't composition affect mass as well though?

with regards

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