What's a planet?, Part II

docm · Feb 21, 2008

http://cosmiclog.msnbc.msn.com/archive/2008/02/20/684017.aspx <blockquote>In reply to:<hr />The next great planet debate Posted: Wednesday, February 20, 2008 3:30 PM by Alan Boyle How do you define a planet? Officials at the International Astronomical Union thought the matter was settled more than a year ago when it drew up a definition of planethood that separated little Pluto from its eight bigger siblings and put it in the dwarf-planet category. Boy, were they wrong. Many astronomers say the definition that the IAU came up doesn't adequately reflect the diversity of worlds we see even in our own solar system - and arguably, might even exclude Jupiter as an official planet. Now a replay of the "Great Planet Debate" has been scheduled for August. Pluto may remain in the pint-size pigeonhole - but the other planets, in our solar system and beyond, would get their own pigeonholes as well. The "Great Planet Debate" is due to begin on Aug. 14 at Johns Hopkins University's Applied Physics Laboratory in Laurel, Md. Here's how the conference is described on APL's Web site: <blockquote>In reply to:<hr />"During the first two days of the conference, we will present what we have learned about planetary bodies over more than 40 years of robotic exploration of the Solar System and what we are learning about planets around other stars. The IAU’s dynamical definition of a planet will be presented, as well as an alternative geophysical definition. The utility of each will be debated, along with other potential planet definitions. "A public lecture and panel discussion, featuring scientists who are prominent in the debate on planet definitions, is planned for the evening of the second day, following a reception that concludes the scientific portion of the conference.</blockquote></blockquote> <div class="Discussion_UserSignature"> </div>

vogon13 · Feb 21, 2008

Are they somehow making money off this ?? Do we really need to 'stir the pot' on this mess again? <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

CalliArcale · Feb 21, 2008

There is very little that arouses the passion of nerds like a semantic debate. <img src="/images/icons/wink.gif" /> So of course the pot will be stirred again. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

wick07 · Feb 21, 2008

There is very little that arouses the passion of nerds like a semantic debate. So of course the pot will be stirred again. And we (humans) are obsessed with classifying things. We have some inner desire to organize the universe into neat little groups, even though it hardly lends itself to that. I think we will be debating this topic for many years to come. <div class="Discussion_UserSignature"> _______________________________ "If you are surrounded by those who constatly agree with you, then you're in an intellectual vacuum. If you feel like trying to make a difference, you have to BE different. How can you do that without interacting with those who are different from yourself?"- a_lost_packet_ </div>

docm · Feb 21, 2008

My definition of a planet; 1. in orbit around a star 2. not heated by internal thermonuclear fusion 3. rounded by its own gravity 4. if two such bodies are orbiting each other and the larger is less than 2x larger than the other they are twin planets. Otherwise they are a planet/moon system. 5. COMPOSITION DOESN'T MATTER. Using composition is a slippery slope that with changing "tastes" could evolve into making the case that gas worlds are not planets. <div class="Discussion_UserSignature"> </div>

robnissen · Feb 21, 2008

And we (humans) are obsessed with classifying things. I completely disagree. You are obviously in the group of humans who insist on classifying things. I, on the other hand, am in the group of humans who refuse to classify things. <img src="/images/icons/smile.gif" />

docm · Feb 21, 2008

You just classified Wick07, and in so doing joined that same classification <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> </div>

chyten · Feb 21, 2008

There are two kinds of people -- those who separate people into two kinds and those who don't. There are 10 kinds of people -- those who understand binary and those who don't.

JonClarke · Feb 21, 2008

I really, really like Mark Sykes' proposed definition. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

JonClarke · Feb 21, 2008

Classification is an essential part of science. The world is not a continuum, there are many discontinuities and patterns that make taxonomies necessary. Both the current IAU and Sykes definitions recongise some of these patterns, what is not yet clear which is the most useful. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

MeteorWayne · Feb 21, 2008

I have to disagree here, Jon. The real problem is that the world (and probably Universe) IS a continuum. Still in order to make sense of it, there are breakpoints that separate useful categories. That's where the art vs science, and the continuous argument exists <img src="/images/icons/smile.gif" /> It really is part of the process of science. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

h2ouniverse · Feb 21, 2008

I am afraid the debate between astrogeologists and dynamicists wil not settle until both have their category. Why not doing what the rest of people do when they have to word different qualities? Use adjectives! This is what they began to do with "dwarf". (and btw saying that a dwarf planet is not a planet is semantically weird, as a dwarf man is a man and a dwarf star is a star...) But "dwarf" should qualify size, not dynamic influence. As opposed to "giant", already used... "Rocky", "Gas", "Icy"... for composition... "Captive" or "Moon" or "Free" for orbiting a star or a planet or nothing... The fact that dynamicists cannot find a simple word to describe a planet that has cleared the orbital neighborhood is unfortunate. But that is not a reason to hijack "dwarf". I would suggest "Dominant" or "Principal". Many adjectives. Why not?

h2ouniverse · Feb 21, 2008

Btw as far as differentiation is concerned, I'm not sure there is such an absolute bijection between size and differentiation. What would you do indeed if you were to find a Callisto orbiting a star?

MeteorWayne · Feb 21, 2008

That's my point. There are no zero breakpoints. When we categorize, we pick points that seperate the (whatever it is) into useful categories. Seldom is there a firm stake in the earth that divides them Those wonderful humans get involved... <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

vidargander · Nov 16, 2008

The term Planet itself is wrong. Therefore any definition of 'Planet' is determined to be wrong too. The term Planet really means ‘Wandering Star’. "The Great Planet Debate" is therefore just as absurd as the pre-Islamic perception of our solar system. The term Globe should be redefined and used by the IAU instead. <div class="Discussion_UserSignature"> </div>

Saiph · Nov 16, 2008

Docm, I agree with all of your stipulations, with one caveat, your requirements for definign a planet and moon system.  The size cutoff you propose is, well, completely arbitrary.  Instead I'd work on where the barrycenter for the orbiting pair is.  If it's between the two bodies, we have a binary planetary system.  If it's inside one of them, we have a primary, and a moon. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

silylene old · Nov 16, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>My definition of a planet; 1. in orbit around a star 2. not heated by internal thermonuclear fusion 3. rounded by its own gravity 4. if two such bodies are orbiting each other and the larger is less than 2x larger than the other they are twin planets. Otherwise they are a planet/moon system. 5. COMPOSITION DOESN'T MATTER. Using composition is a slippery slope that with changing "tastes" could evolve into making the case that gas worlds are not planets. Posted by docm</DIV>1. in orbit around a star  Should say "in a stable orbit around a star or stars"4. if two such bodies are orbiting each other and the larger is less than 2x larger than the other they are twin planets. Otherwise they are a planet/moon system.  I agree with Saiph's definition below much better.Replying to: <DIV CLASS='Discussion_PostQuote'>Docm, I agree with all of your stipulations, with one caveat, your requirements for definign a planet and moon system.  The size cutoff you propose is, well, completely arbitrary.  Instead I'd work on where the barrycenter for the orbiting pair is.  If it's between the two bodies, we have a binary planetary system.  If it's inside one of them, we have a primary, and a moon. Posted by Saiph</DIV> Agree on the barycenter.  But to be a bit picky on the orbiting pair system, if one of these two bodies is undergoing thermonuclear fusion, it also cannot be defined as a 'planet and moon system'.  In that case it is a planet orbiting a star, both of which orbit the primary star.  [I know you meant this, and perhaps it is unnecessary since you said 'planet and moon system.' <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center">- - - - - - - - - - - - - - - - - - - - - - </div><div class="Discussion_UserSignature" align="center">I really, really, really miss the "first unread post" function. </div> </div>

Saiph · Nov 16, 2008

I actually figured point I in Docm's list...but I see where I mispoke

nitpicker   <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-tongue-out.gif" border="0" alt="Tongue out" title="Tongue out" />  <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

MeteorWayne · Nov 17, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'> 4. if two such bodies are orbiting each other and the larger is less than 2x larger than the other they are twin planets. Otherwise they are a planet/moon system. Posted by docm</DIV> This should really be defined by mass rather than "size" <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

UFmbutler · Nov 18, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>1. in orbit around a star  Should say "in a stable orbit around a star or stars" Posted by silylene</DIV>Well, that depends on your definition of "stable".  For example, the exoplanetary system 55 Cnc is now believed to have chaotic orbits, but the system as a whole is stable over the long term.  However, you would certainly not call the individual planets stable.  I talked with someone involved in the debate(Alan Boss, he did a ton of interviews about Pluto back in 06 when it was announced) at a conference a few weeks ago, and it seems that, on a professional level, people don't really care whether you call something a planet or a dwarf planet...if it's interesting, they will study it.  Sure, in a proposal "planet" sounds more exciting than "Kuiper Belt Object" but that's only because the current definition of planet is so strict.  If we called everything a planet, it would quickly lose its meaning.    <div class="Discussion_UserSignature"> </div>

Philotas · Nov 18, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>1. in orbit around a star  Should say "in a stable orbit around a star or stars" Posted by silylene</DIV>Ejected planets? Planets that formed alone?Replying to: <DIV CLASS='Discussion_PostQuote'>If we called everything a planet, it would quickly lose its meaning.    Posted by UFmbutler</DIV> The term 'star' could also refer to extremely different objects; from the small and long-lived red dwarves to the blue and short-lived hyper giants that may end up as stellar black holes. <div class="Discussion_UserSignature"> </div>

vidargander · Nov 19, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>http://cosmiclog.msnbc.msn.com/archive/2008/02/20/684017.aspx In reply to:The next great planet debate Posted: Wednesday, February 20, 2008 3:30 PM by Alan Boyle How do you define a planet? Officials at the International Astronomical Union thought the matter was settled more than a year ago when it drew up a definition of planethood that separated little Pluto from its eight bigger siblings and put it in the dwarf-planet category. Boy, were they wrong. Many astronomers say the definition that the IAU came up doesn't adequately reflect the diversity of worlds we see even in our own solar system - and arguably, might even exclude Jupiter as an official planet. Now a replay of the "Great Planet Debate" has been scheduled for August. Pluto may remain in the pint-size pigeonhole - but the other planets, in our solar system and beyond, would get their own pigeonholes as well. The "Great Planet Debate" is due to begin on Aug. 14 at Johns Hopkins University's Applied Physics Laboratory in Laurel, Md. Here's how the conference is described on APL's Web site: In reply to:"During the first two days of the conference, we will present what we have learned about planetary bodies over more than 40 years of robotic exploration of the Solar System and what we are learning about planets around other stars. The IAU’s dynamical definition of a planet will be presented, as well as an alternative geophysical definition. The utility of each will be debated, along with other potential planet definitions. "A public lecture and panel discussion, featuring scientists who are prominent in the debate on planet definitions, is planned for the evening of the second day, following a reception that concludes the scientific portion of the conference. Posted by docm</DIV>StarTrek does a far better job than IAU.http://en.wikipedia.org/wiki/Star_Trek_planet_classifications... pity that is true. <div class="Discussion_UserSignature"> </div>

What's a planet?, Part II

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