Is {pluto|sedna} A Planet?

Dr. Zowie writes "NASA's announcement last week of Sedna's discovery reignited the debate over whether Pluto is a planet. Dr. Alan Stern a noted planetary scientist and leader of the New Horizons mission to Pluto, pours on some gasoline with this article in which he skewers the various arguments against Pluto-as-planet. Choice quotes include 'You wouldn't deny a chihauhau a place among dogs because it is too small,' and 'if your brain was so completely full of names of people that it just couldn't take any more, would anyone new who you met after that, therefore not be a person?'"

Comments

Re:Asteroids?

[korielgraculus]

Th proposal in the article is that every body that is rounded by it's own gravity (apparently this happens at a few hundred kilometres) should be considered a planet. Actually sounds a reasonable definition to me.

You say Brontosaurus, I say Apatosaurus

[TrentL]

The Atlantic Monthly had an article about the Pluto situation years ago. The problem, though, is that "kids love Pluto." Scientists have tried to change names before (such as the dinosaur example). It'll be interesting to see what the public says about Pluto's demotion (if it occurs).

Re:You say Brontosaurus, I say Apatosaurus

[pavon]

Again, kids are very flexible about learning new things. They latched onto that Aptosaurus like nothing. Actually I think they kind of enjoyed being able to correct all the adults that still called it brontosaurus.

If you were to tell them that we have learned that Charon is not really a moon of Pluto, but that they are close to the same size so they revolve around each other like people dancing, they would think that is really cool. If you further went on to tell them that we have found out that there are a whole bunch of icy subplanets like Pluto and Charon but smaller, and maybe one day we will find one that is bigger, and maybe they could be the one to find it, they will get even more excited about astronomy.

Honestly, it is the adults that are stubborn about keeping the status quo, not the kids.

Re:Asteroids?

[Xzzy]

Honestly, who cares.

It's not like there's some legal reason to have the definition of a planet rigidly defined, it doesn't effect the money anyone gets, it doesn't influence political boundaries, and it won't get anyone out of jail.. so who cares? :P

If it's big, it's a planet. If it's not big, it's an asteroid. If it's not big and made of ice, it's a comet.

Might as well debate which text editor is bettor or whether we should be putting GNU in front of Linux.. it's such a silly thing to discuss it baffles me this shows up in the news so often.

Approach to understanding the solar system.

[pavon]

I think part of the problem is the fact that memorizing the 9 planets are all most people really know about our solar system, and so they tend to be fairly sentimental about it. I think a much more accurate and interesting approach to teaching kids would be to start of by brainstorming all the different types of objects in space - galaxies, solar systems, stars, moons, astroids, comets, nebulas. Then instead of memorizing just the planets memorize all the different regions of our solar system and what makes them special. Start with the sun, then you get to the inner planets, then astroid belt made mostly of rock, then giant gass planets, then the Kupier Belt full of icy objects and finally the Oort cloud. Then lastly you describe the interesting features of each area, including the planets and what makes them unique.

This journey approach would be far more interesting to the kids and by the time you got to the point of describing pluto and charon, they would have an understanding of how diverse (for lack of non PC word) matter in space is and would be less concerned about sticking a specific catagory on it, and just be excited that it was yet another unique and interesting thing.

It's the difference between decribing the cool terrain, people and features in country as opposed to just memorizing the state capitals. The former is far more interesting, and informative, and kids will eat it up.

Re:Requirements? Look to gravity!

[Chris Burke]

How about the simple argument that planets are gravitationally strong enough to pull themselves into nearly spherical objects, whereas asteroids are not.

I like this definition a lot. While it does leave some wiggle room as to what exactly constitutes "spherical", it is still based on a physical property of the object related to its mass. This makes it better than any arbitrary size/mass requirement (e.g. "Anything as big or bigger than Pluto").

Pluto, BTW, Sedna, and many of the largest moons can all do this.

I'm going to be extremely unhappy with any definition that demotes Pluto. Also, anything that makes Pluto not a planet is going to be close to making Mercury not a planet, and that's just not acceptable. :)

I also think, for the record, that if something as large as Luna, or Titan, or Europa were out floating in space orbiting the sun and not another planet, they would be considered planets too.

Titan is bigger than Mercury, so a Sun-orbiting Titan not being considered a planet is unacceptable. :) But clearly a planet-sized object orbiting another planet is a moon. Again, this definition makes perfect sense.

I'm not an astronomer (but I play one on occasional weekends), but of all the definitions I've heard, "big enough to be spherical and orbiting a star" is the simplest and most logical.

And for the record -- if there was some comet out in the Ort cloud with an incredibly eccentric orbit around the sun that was the size of Titan, that'd be a planet too. IMHO. :)