Experts meet to decide Pluto fate, Finally we'll know what a 'planet' is... Options

[Stephen]

"Really? In that case North America and South America (like Europe, Asia, and Africa) are only a couple of subcontinents too.

"All of which would bring the number of continents down from seven to four: Afro-Eurasia, America, Antarctica, and Australia."

Not necessarily. India is a separate plate that happens to be ramming into Asia. North and South America are also separate. But Europe is not a separate plate.

What have plate tectonics got to do with whether a particular landmass is called a continent or not?

======
Stephen

[djellison]

"Now New Horizons has fresh purpose, [ Caltech planet-hunter Mike] Brown said in a telephone interview.

imho - that's bull. NH is going to study Pluto, Charon and their two small moons. Pluto is still a Pluto. It's not changed. The mission has not changed. The body it's going to visit remains a member of the same family of bodies it always has.

Doug

[tedstryk]

What have plate tectonics got to do with whether a particular landmass is called a continent or not?

======
Stephen

Every other continent has an associated plate, with a few minor ones attached at times...Europe and Asia share one. The division between Europe and Asia has no geological sigificance, while the division between India and the rest of Asia does...

[Jyril]

The wording of the resolution screams "Arbitrary!" And frankly, it is about as inspiring as the kind of crap the U.N. spews (for the record, my comment does not refer to the U.N.'s usefulness, but the convoluted way it tends to word things).

I'd like to hear of a definition of a planet that is not arbitrary.

Let's scrap that orbital clearing part. That left us with round non-satellites. Why a planet can't be a satellite? Why it has to be round at the first place? There's planetary mass objects that don't orbit any star. Hey, let's call all non-fusing objects planets, from dust particles to brown dwarfs! No, why arbitrary limit of fusion? Let's call any object a planet! You are planet, I'm a planet. Now we all are happy.

[odave]

NPR's All Things Considered had a good segment on the Pluto dust-up. There's some audio from the conference as well as a short interview with Michael Brown.

One thing I found amusing in the conference audio was when one member challenged the orbit clearing clause, stating that Neptune should not be a planet since Pluto crosses its orbit. The response was "footnote 1", which defines the "classical 8" as planets, including Neptune. Someone then suggested they scrap the resolution and leave the footnote

[ngunn]

New mnemonic from the IAU?

Majority Vote Ends Matters - Just Shut Up Now!

[Betelgeuze]

Majority Vote Ends Matters - Just Shut Up Now!

I didnt vote!

[Alan Stern]

I didnt vote!

And neither did 96.2% of the IAU's 8900 members: they weren't even allowed to vote if they were
not in Prague. This story is about to break.

[Greg Hullender]

Alan: May I ask whether the committee considered the term "planetoid?" It seems it would be very useful to have a single term for bodies large enough to be rounded but not large enough to fuse. A term that's strictly independent of orbital dynamics. Also, I don't believe it already has any formal definition.

Was it just because the term has been overused in science fiction? It seems such an obvious choice I can't believe it didn't come up.

[mars loon]

And neither did 96.2% of the IAU's 8900 members: they weren't even allowed to vote if they were
not in Prague. This story is about to break.

Thats an excellent point I've been thinking about too.

[Stephen]

Every other continent has an associated plate, with a few minor ones attached at times...Europe and Asia share one.

The division between Europe and Asia has no geological sigificance, while the division between India and the rest of Asia does...

Define "minor".

1) The Caribbean plate contains a large chunk of Central America. Arabia has a plate all of it own. (So does India.) If North America and South America are entitled to be classed as separate continents because they each have their own plate why not those other chunks?

If "the division between India and the rest of Asia" is of "geological significance" why not the divisions between other plates, such as the one between Arabia & the rest of Asia and between the chunk of Central America on the Caribbean plate and the rest of the Americas?

Or is the "geological significance" in India's case those impressively tall mountain its ramming into Asia has managed to push up? If so, what is the "geological significance" of the boundary between the continents of North America and South America?

2) Which raises the related issue of where do you divide North America from South America: at the northern boundary of the South America plate or at the northern boundary of the Caribbean plate? That is, if that chuck of that chunk of Central America on the Caribbean plate is not a separate continent is it part of the continent of South America or part of North America?

3) Then there's the fact that the North American plate includes Greenland and part of eastern Siberia. Does that mean those are part of the North American continent as well (just as Europe, being part of the same plate shared by most of Asia, means that Europe and Asia are part of the same continent under your scenario)?

True, there's all that water in the Bering Strait. However, during the last ice when sea levels were much lower than they are today North America was connected with that chunk of east Asia which is part of the North American plate (just as Tasmania and New Guinea were connected with Australia--although not Australia with Asia--and the British Isles with Europe).

Does that historical connection between East Asia and North America increase the likelihood of that chunk of east Asia making it into part of the continent of North America under your model or does all the water now in the Bering Strait still get in the way?

The point here what kind of boundary marker predominates in your model when deciding where the divisions between continents lie? Geographical ones like water or geological ones like tectonic plate boundaries?

A case in point: you are argue that the "division between Europe and Asia has no geological sigificance". As it happens that division traditionally runs along geographical boundaries such as the Ural Mountains and the Black Sea. If the Black Sea has "no geological significance" as a boundary between Europe and Asia what pray tell is the geological significance of the Bering Strait between Asia and North America?

****

The reality is that the concept of "continent" was around long before plate tectonics came into vogue. So was the division of Afro-Eurasia into three continents and the American continent into two. Boundaries of "geological significance" have little to do with defining them. Geography and history were used to decide those divisions, not geology.

A continent was and still is basically a large landmass surrounded by water, but with historical considerations tempering the division. (For more, see this Wikipedia page.)

It seems to me you're using plate tectonics in a novel way to try to retroactively justify elements of the historical divisions more than elements of the geographical ones, but in what seems to me to be a potentially inconsistent fashion.

======
Stephen

[Alan Stern]

Alan: May I ask whether the committee considered the term "planetoid?" It seems it would be very useful to have a single term for bodies large enough to be rounded but not large enough to fuse. A term that's strictly independent of orbital dynamics. Also, I don't believe it already has any formal definition.

Was it just because the term has been overused in science fiction? It seems such an obvious choice I can't believe it didn't come up.

No, not considered by the IAU.

[Jyril]

There is aready the horrible-sounding term "planemo" (planetary mass object) which means exactly that.

[David]

Every other continent has an associated plate, with a few minor ones attached at times...Europe and Asia share one. The division between Europe and Asia has no geological sigificance, while the division between India and the rest of Asia does...

I've more often seen India and Australia shown as part of the same plate (Indo-Australian plate). Perhaps India and Australia should be reclassified as a "double continent".

[JRehling]

[...]