@ MTU et al. – On the discussion over Pluto’s status…How about we leave it to the professional astronomers to define their terms, hmmm? If they want to include terms about gravitationally dominating a region of space, then let them. If they want to define planets by colour (they don’t, to the best of my knowledge), then that also is their prerogative.After all, no-one here owns those things out there, so let’s just leave it to those who study such things for a living.

Three things about that :

1) That’s a fallacy of authority right there. Just because an “expert” says something doesn’t mean its right. There are cases where scientists get it wrong – even Einstein admits to some blunders while it was common for scientists such as Lord Kelvin to deny the possibility of heavier than air travel and especially space travel at one time.

2) The professional astronomers themselves disagree on this issue. Alan Stern, for example, called the IAU definition “idiotic”, Ken Croswell has spoken out against it as have others. The IAU meeting that made the decision was in many ways rather dubious and questionable.

3) I’m an astronomer myself – albeit an amateur rather than a professional one!

no-one here owns those things out there,

Tell that to the Spanish lady who thinks she owns the Sun!

(Not that I recognise her claim in any way shape or form – joking there ‘k.)

This is the article I have been looking for to ask this question…
Will someone please explain the numerous constellation/star/sky Mapping software; (GOOGLE EARTH, MICROSOFT, BING, POSSIBLY OTHERS?) THAT ALL HAVE THE EXACT SAME PART OF THE SKY, EDITTED OUT BY A BLACK SQUARE ABOUT 2X2 INCHES WIDE…. I have found it and forgive me for my lack of coordinate reading skills but this is where I found it on Google Earth:

RA 5h53m43.76s Dec – 5 59’37.52” 0 02’00.91” arcdegrees

On the discussion over Pluto’s status…

How about we leave it to the professional astronomers to define their terms, hmmm?

If they want to include terms about gravitationally dominating a region of space, then let them. If they want to define planets by colour (they don’t, to the best of my knowledge), then that also is their prerogative.

After all, no-one here owns those things out there, so let’s just leave it to those who study such things for a living.

I disagree. Neptune and Jupiter are located amidst belts of objects – their own trojans; comets cross all planet orbits thus rendering them technically “unclear” and “fairly clear” to who anyhow?

Are you saying you can see no distinction between Jupiter (mass 317 times that of Earth) and the Jupiter trojans (total mass approximately 0.0001 times that of the Earth) because they are located in a similar region of space? Really?

Or to take an analogy, imagine a box filled with large numbers of iron filings and also a small number of iron cannonballs. Would you argue that the cannonballs cannot be regarded as distinct from the iron filings? That is what you are doing when you are saying that you cannot distinguish Jupiter from the various debris located around its orbit.

Let me make this very clear for you: JUPITER IS NOT A MEMBER OF THE JUPITER TROJANS. If you think there is any case to be made that Jupiter is a member of this population, there is no hope for you. Plot the distribution of masses of objects crossing its orbit and it is such an extreme outlier that there can be no question about this.

I think another reason things like this go viral is because people are only reading the titles of articles “New Giant Planet Orbiting The Sun” leads people to believe that’s what is going on. If you read the articles they (not all, but some) tell you it’s not a fact and it’s just an idea/possibility.

As a new astronomer, this is my number one source for the truth to other articles I might read that stretch the truth or twist it in a way to make you believe that possibility is fact. I’m trying to turn my blog into an astronomy blog but I can only do so much with the little knowledge I have on the subject. Don’t want to lead people in the wrong direction by stating something that isn’t true.

Thanks Phil, for this blog.

-Mike

@Messier Tidy Upper: stop obsessing over the semantics of the IAU definition.

I’ll thank you NOT to tell me what to do with *my* life just as I’m not going to tell *you* what to do with yours.

It is fairly clear what is meant is “not a member of a belt of objects”, and none of the 8 major planets are.

It is? Really? I disagree. Neptune and Jupiter are located amidst belts of objects – their own trojans; comets cross all planet orbits thus rendering them technically “unclear” and “fairly clear” to who anyhow? Is the IAU definition good enough and really one that works? I don’t think so!

Pluto turns out to be a member of the Edgeworth-Kuiper belt ..

Just as our Earth turns out to be a member of the inner solar system region and the gas giants are located in what we now know is the “middle zone” of our solar system. Big deal.

..and is thus not a planet by a reasonable dynamical criterion,

You think the orbital dynamical criterion is reasonable then? I do not.

As long as a planet isn’t directly orbiting another planet and thus becomes a moon rather than an independent globe then I don’t think its orbit matters in terms of its definition as a planet. As I’ve already noted in comment #136, we now of many planets that are in very strange and far more eccentric orbits than Pluto’s case.

..and also by historical precedent dating back to the demotion of Ceres and other asteroids.

Funny you should mention Ceres there. It was originally considered a planet, got temporarily demoted then more recently promoted halfway back. I hope Pluto’s demotion is likewise a temporary aberration, a mistake that gets fixed and that Ceres also gets returned to planet status.

Furthermore your fusion criterion is demonstrably inadequate to describe several observed exoplanetary systems, e.g. Upsilon Andromedae, BD+20 2457, Nu Ophiuchi…

That’s a more interesting note there. I would be happy to class such examples as brown dwarfs instead of exoplanets but I agree there may well be overlap between the brown dwarfs & highest mass superjovian categories. There is scope for an interesting debate there – but such cases certainly don’t exclude Pluto from planethood. Unless that is you’re claiming Pluto is a brown dwarf!

@116. CB :

Why would you create a definition where the reasonably probable case of there existing an object of slightly lower mass than Ceres (or slightly greater mass if you meant Ceres was the biggest a dwarf planet could be), raising the question of why it doesn’t qualify and Ceres does? Instead, why not pick a criterion for which no arbitrarily precise line needs to be drawn, because the distinction is huge and obvious?

Um.. yeah Like gravitationally forced roundness for instance?

It’s like the IAU is distinguishing between Eurasia and the Americas by saying they’re separated by the Atlantic Ocean, and you’re saying no that’s confusing, let’s distinguish Europe and Asia by drawing some arbitrary line through it. Yeah, that’s so much better and less confusing.

No, its like the IAU saying that Australia and Antartica are islands instead of continents because they’re small & not joined up with other landmasses.

Planets can be located in asteroid or comet belts.

Tell that to the IAU, its not what their definition says!

The question is, does the planet dominate the orbit or is it dominated by the belt objects? That’s the difference between Neptune and Pluto, and it’s a 10^6 difference so not exactly a matter of drawing an arbitrary line.

Except that Pluto does dominate its orbit – it holds Charon, Hydra and Nix inits thralland has other bodies suchas Orcus (I think it is) locked into a relationship where it stays away from Pluto. That gets into the semantics of what is meant by “domination” etc ..

This hypothetical object in earth’s orbit — did it break up because earth’s gravity was enough to tear it apart? Then it would certainly be of small enough mass that earth’s orbit would still be called clear. If it isn’t, then why exactly did it break apart, with all the pieces in stable earth-like orbits? Because you willed it to be so? Well you could will Pluto to have enough mass to clear its orbit, but it doesn’t, so what?

It doesn’t matter for the purpose of this hypothetical – in fact there could be many hypotheticals where each of these scenarios is considered.

If and when cases in the currently unoccupied grey area show up, and our understanding of orbital dynamics increases to encompass them, then we can worry about improving our definitions to accommodate them, based on reality, not hypotheticals.

Just like the neutrino, brown dwarfs & black holes were purely hypotheticals that scientists just scornfully dismissed and completely ignored until they were found?

Oh wait, no, the exact *opposite* actually happened!

Science works on hypothesising and imagining – then observing and finding.

It seems nature builds planets in a range of sizes from superjovian near brown dwarfs to ice dwarfs like Pluto. Let’s not ignore possibilities and rule them out withoutr good reason to do so.

Let’s have the foresight and imagination to adopt a suitably broad and incluusive definition that allows space for us to all sorts of planets and planet types – and the menagerie of alien worlds we’re finding keeps getting ever stranger and more wonderful!

Planets come in a vast range of sizes, masses, compositions and orbits* from worlds far bigger than Jupiter that are on the boarderline with brown dwarfs and made almostentirely of gas are at one extreme. The continuum of objects nature builds then ranges down through ice gianst or gas dwarfs like Neptune and Mustafar-like superEarth’s like CoROT 7b and Kepler-11b through to worlds like Earth and Mercury that are mostly rocky. All the way to the most familiar idea of planet to most people – probably. All the way to the other extreme of the planetary continuum where we have worlds like Pluto and Sedna that are made of rock and ice that are boarderline to asteroid or comet nuclei.

Earth has more in common with the latter ice dwarf worlds than the former gas giant ones. In some ways it would make more sense to say gas giants aren’t planets but rather something very different in nature than the ice dwarfs!

To paraphrase Dr Suess : A Planet’s a planet no matter how small!

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* Like The Comet-orbit planet or ‘Icarus’ planet HD 80606b the mostextreme of a whole large class of eccentrically orbiting exoplanets. See “Weather sizzles on a planet that kisses its star” posed on this BA blog January 28th, 2009. There are also planets such as HD 45364 b & c that are analogous to Neptune & Pluto in their orbital relationship. (See Ken Croswell’s article ‘Extrasolar Neptune-Pluto Analogue Discovered’ posted on February 18, 2009 avail on his website.)

We wouldn’t deny these worlds the title of Planet so why treat Pluto & the other ice dwarfs so badly?

@MTU : “No, I understand the IAU’s definition quite well thankyou. I just strongly disagree with it and I have already explained why many times here before.”
Yes, and I’ve read them, and they always seem to involve serious misconceptions, like that a 4x-Jupiter-mass object in the Oort cloud would necessarily be a dwarf planet. It almost certainly would not, any more than Neptune is a dwarf planet because of the many KPO objects in its neighborhood which combined are less than 1/10000th of its mass.

But it would still be located in an “unclear” orbit so would still not count as a proper planet but would be termed a dwarf instead.

You claim my arguments are misconceptions, I maintain that they’re accurate conceptions. We see this very differently.

But I don’t see any confusion, except created by those trying to find a way to discredit it by saying it causes confusion.

You aren’t the only person on the planet. Just because *you* are not confused does NOT mean other people feel the same as you do. Can you not see how others could find things confusing and that a clearer, simpler, better definition would be, well, better?

There isn’t a single known object in the solar system whose categorization by the IAU definition isn’t perfectly clear.

O really?

I don’t think that’s actually the case – I think there is considerable doubt among many people over what the status of dwarf planets is – and I can point to textbook examples for you – same for Ceres and others. Ill also note that there are many astronomers who disagree with and reject the IAU definition too. See what Alan Stern had to say about it for instance.

When there’s a 4 order of magnitude difference between the greatest of the dwarf planets, and the least of the planets, nobody should be confused.

Do you mean apparent magnitude as in brightness or metaphorically magnitude as in mass /size range?

Do you mean planets as in the planets of all stars or just those found in our solar system?

Ironically, I find your assertion there potentially confusing.

“Or as in the case of defining hill versus mountain we could just set an arbitrary cut-off point which I suggest be the size of Ceres.” [Me.]

Why would one define an arbitrary cut-off, when there’s an actual difference between objects based on their orbits?

Because the differences in orbits really aren’t that great or I think significant – Pluto and Eris have inclined orbits eccentric orbits but then so does Mercury to a lesser extent. Pluto and Ceres have other bodies orbiting with them but then so too does Neptune and Jupiter – remember their trojan co-orbitals?

Also because there’s a far more obvious and better defining quality that raises far fewer problems than orbit – and that’s roundess.

Planets come in a vast range of sizes, masses, compositions and orbits from worlds far bigger than Jupiter that are boarderline to brown dwarfs and made of gas through to worlds like Earth and at the other extreme of the continuum worlds like Pluto that are made of rock and ice that are boarderline to asterpoid or comet nuclei. Earth has more in common

To paraphrase Dr Suess : A planet’s a planet no matter how small!
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