What makes a planet a planet?(lower limit)

[Philotas]

<span method="POST" action="/dopoll.php"></span> <br /><br />The defintions above(apart from the <b>4.</b> option) are in addition to:<br /><br />A planet has to(alternatively)orbit a star(s); and (not alternatively) not be a satellite of another planet.<br /><br />If you think that planets are still planets if they are not orbiting a star or any other object(i.e “floating” in interstellar space); but that moons are not planets, then vote for either <b>1</b>, <b>2</b>, <b>3</b> or <b>5</b>.<br /><br />If your defnition is missing; vote <b>other</b> and explain what it is like, if that`s the case<br /><br />If you only partially agreee with a definition, please vote for it and explain below why/how you disagree with it.<br /><br />This is thread is about <i>major</i> planets. <br /><br />-------<br /><br />Lots of threads have been on this subject, but not a poll(there was one about how many planets there were in the solar system, but <div class="Discussion_UserSignature"> </div>

 

[mikeemmert]

"Other" - It follows the Titius-Bode law of planetary spacing and is the largest object in that orbit.<br /><br />Ceres and 2005 FY9 are planets; Pluto and Xena are not. If another object larger than 2005 FY9 is found in the same orbit, 2005 FY9 is demoted and replaced by the other object.<br /><br />Pluto and Xena are plutinos or scattered disc objects and were once Lagrangians. KBOs are separated into cubewanos and plutinos, the "twotino" and scattered disc objects are subsets of plutinos.<br /><br />If something like "Nemesis" is discovered, we analyze it and make the announcement when this process is finished. Nobody knows what it's like, those of us who have investigated have several equally-likely scenarios, and the thing might not even exist!<br /><br />A planetary definition has to work for other stellar systems. A big problem here is that most systems found so far seem to be unstable and the neat Titius-Bode spacing has been trashed.<br /><br />If we find a life-bearing moon around another star's planet, can it be called a moon or is it a planet?<br /><br />All this is really complicated...

 

[bonzelite]

<font color="orange">All this is really complicated...</font><br /><br />right. so why complicate it further. <br /><br />planet is round. orbits the sun. <br /><br />that's it.

 

[Philotas]

Your link:<br />"Neptune violates the law (by falling halfway between k=64 and k=128)." <br /><br />That`s nasty! <div class="Discussion_UserSignature"> </div>

 

[nacnud]

<font color="yellow">planet is round. orbits the sun. <br /><br /><font color="white"> I hope you have a good menory, there are likely a couple of dozen of those</font></font>

 

[bonzelite]

but that is the dilemma. we either demote Pluto, have only 8 planets forever, or we keep finding round worlds in the K-belt, and the number of planets climbs to hundreds. <br /><br />the double standard, perhaps, too, is that nobody has a qualm with racking up more and more moons around jupiter, saturn, neptune, uranus, etc. you can have scores of moons around only one planet. and nobody cares about that. there are so many moons that most people have no idea of their existence. <br /><br />but you then say only <i>one more "planet,"</i> and everyone runs scared sh$$%%less and doesn't know how to act. <br /><br />

 

[nacnud]

I know, but how about 'minor planet' for anything round orbiting the sun and 'planet' for the other eight.<br /><br />Reasoning the eight are special<br /><br />History<br />Close to the ecliptic<br />Circular orbit<br />...?

 

[mlorrey]

Cutting it down to eight planets just so elementary school kids can memorize them all is stupid. There are billions of billions of planets in the universe, we might as well start getting used to that fact, and get people used to a realistic scope of an idea that there is more knowledge in the universe than they can fit on a pop quiz.

 

[rhm3]

Agree...a planet is a gravationally-shaped spheroid that doesn't fuse. A world. <br /><br />Planets can be divided into 3 major classes based on this...classical, rogue, moon. I think spheroid moons should technically be planets too. Are animals no longer animals if they're domesticated? Plus it doesn't feel right calling Varuna a planet but not Titan. <br /><br />Teach kids the main 8 ones plus teach that there's a bunch of ice planets after Neptune...and also add that gas giants have some cool moons (planets) too. That's still fun and interesting. The fact that the asteroid belt has 2 small planets is a cool bonus trivia.

 

[mikeemmert]

<blockquote><font class="small">In reply to:</font><hr /><p>A world.<p><hr /></p></p></blockquote>Now how about that word?

 

[mikeemmert]

<blockquote><font class="small">In reply to:</font><hr /><p>Your link: <br />"Neptune violates the law (by falling halfway between k=64 and k=128)." <br /><br />That`s nasty! <p><hr /></p></p></blockquote><br />They're all nasty.

 

[mikeemmert]

Tell you what's nastier. Plutinos and cubewanos all mixed up together. But they're seperate populations. And what about Buffy? That's probably in the same population as Sedna, but how would I know? I'm just a lowly asteroid...

 

[bonzelite]

<font color="orange"><br />Cutting it down to eight planets just so elementary school kids can memorize them all is stupid. There are billions of billions of planets in the universe, we might as well start getting used to that fact, and get people used to a realistic scope of an idea that there is more knowledge in the universe than they can fit on a pop quiz.</font><br /><br />+10

 

[mikeemmert]

Biology is worse. That's why they have classifications. They don't confront kids with Tuataras.<br /><br />It's easier to remember classifications than individual animals. Same with astronomical objects. If we find other life, then the teacher saying, "Xanadu is the Lagrangian of a dead brown dwarf circling an F-type star in Hercules" would have the kid knowing a lot more than just "planet".

 

[bonzelite]

i see there's no middle ground here. it's either super speciifc designations for a minority of killjoy technophiles, or it's the more relatable basic idea of "planet" that can be explained later for particulars. <br /><br /><br />

 

[Philotas]

Good, good. Join the 'All round thingys are planets' movement. We are fighting for justice. <div class="Discussion_UserSignature"> </div>

 

[Philotas]

Ok, so you`re saying that planets should be classified after where they were formed; that way Neptune is still a planet. <div class="Discussion_UserSignature"> </div>

 

[mikeemmert]

OK, thanks Philotas. I think that's a much simpler way to put it. There was some confusion when somebody tried the definition, "<i>How</i>" they were formed, but that actually added more confusion. I wish I could remember who that was or where I saw that (not on this forum). Where (Titius-Bode, Lagrange, other resonance, planetary orbit, perturbed location, etc) works much better.<br /><br />The largest Lagrangians are bigger than the smallest Titius-Bode objects. So this might bring back the arbitrary size definition, which seems centered around 2000 km. So we have Titius Bode planets, ten of them (Ceres and 2005FY9 are included), Lagrangians, two of them (Pluto and Xena), Oort planets, one so far (Sedna) and whatever might come up in the future. I hope the kids can remember 13 planets!

 

[Philotas]

<font color="yellow">I hope the kids can remember 13 planets!</font><br /><br />I`m afraid they wont. It`s hard for kids to remember even 9 planets; once you go above that, most wont remember them all.<br /><br /><br />Anyways, these are the results so far:<br /><br /><br /><br /><b>What is the lower limit for a planet?</b> (Total Votes: 14) <br /><br /><br /><b>It`s shaped roughly circular by its own gravity</b><br />4. <i>(28%)</i> <br /><br /><b>Equal to the size of Pluto, or bigger </b> <br />3. <i>(21%)</i><br /> <br /><b>It is big, roughly circular shaped, and doesn`t share orbit with similar sized objects</b><br />3. <i>(21%)</i><br /><br /><b>All roughly circular shaped objects are planets</b> <br />2. (<i>14%)</i><br /><br /><b>Other</b><br />2. <i>(14%)</i> <br /> <br /> <br /><br />Hoping for a few more votes. <br /> <br /> <div class="Discussion_UserSignature"> </div>