I had a quick look at the defintion of Clearing the Orbit on Wikipedia[1] and it answers the question about objects like trojans, Pluto re: Neptune and Cruithne re: Earth. The controversy section doesn’t have a neutral feel it. And the IAU link is dead so, I couldn’t easily check the IAU definintion.

Having a seemingly clear term or even a catchy phrase can often be more of a curse because you end up setting false expectations and then backtracking to explain and educate. You often make your task harder.

Aside from false expectations, the other thing that happens when you try and explain this to regular people is that they aren’t going to get it. You can almost hear the sound of eyes glazing over. Frankly, the public would have been happy with two or three simple modifiers like minor, major, and giant leaving details to scientists. Actually, from a public perspective this works with Ceres. I’ve had parents and kids ask questions about asteroids get surprised when you describe Ceres because they think all asteroids are either (a) not large and round and (b) in wild orbits (okay too much Star Wars).

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[1] http://en.wikipedia.org/wiki/Cleared_the_neighbourhood

Term “clearance of orbit” is maybe unclear (heheh) and I prefer term “gravitational dominance”, but definitnion of “clearing of orbit” do NOT require clearing every little speck of dust on path of body. Yet I see some inane comments about just that, especially StevoR’s.

Especially funny is rant about Earth crashing with body that gave us moon. Someone would thought that planets was not YET formed, and all bigger bodies would be called “protoplanets”, each own with future as part of bigger body of “planet” in future (in about few tens of milions years). In other words, StevoR search for planets in bad place (protoplanetary discs) and in wrong time (young solar system in process of formation).

Next thing - trojan asteroids or Pluto crossing Neptune… these cases are reason why I prefer term “gravitational dominance”. It is just easier to explain. Pluto and trojans exists here and now ONLY because planets Jupiter and Neptun gravitationally controls them. Case: Pluto has 3:2 resonance. Orbit of Pluto and Neptune never crosses in sense that Pluto never ever will be in same place as Neptun in same time, because Neptun controls Pluto.

This is why I cannot stand “buut Pluto, buut trojans” idiocy. I repeat: clearing of orbit do NOT require eradicating every little speck of dust. Thank you for your uncooperation.

PS: oh, one more little thing. Gravitational roundness IS arbitrary. Maybe less arbitary than hardcoded size, but still. Why? Because it depends on composition of body in question. Small icy bodies will faster be round than rocky. And what composition of body have to status of planet?

The argument that we can’t have too many planets because children will be unable to memorize them is ridiculous. Memorization is not as important as is understanding concepts such as gas giant, terrestrial planet, etc. The solar system was not designed for our convenience. If it has 200 planets, then that is what it has. Arguing for eight out of convenience is like arguing we should limit the Periodic Table of the Elements because there are too many to learn. Having over 100 planets does not “degrade” the term or concept of planet any more than having billions of stars degrades the term star or having billions of galaxies degrades the term galaxy. As for the statement that we will never visit these objects–well, we already are with New Horizons and likely will do so with additional missions in the future.

The case of Ceres’ demotion is actually a good parallel because that demotion was equally wrong. However, in the mid 19th century, no astronomers knew that unlike the other objects in the asteroid belt, Ceres is in fact round, in hydrostatic equilibrium. This was first discovered in the 1990s. Now that we have this knowledge the appropriate action is to designate Ceres, Pluto, Eris and the round KBOs as planets. They can be subclassified as dwarf planets, but to state, as the IAU did, that dwarf planets are not planets at all makes no linguistic sense. In contrast, astronomy still recognizes dwarf stars as stars and dwarf galaxies as galaxies.

Dan Fischer, you are just plain wrong in stating that the opposition to Pluto’s demotion comes from a “small minority” of astronomers. Yes, Mike Brown supports the IAU definition, but 300 professional astronomers rejected it in a public petition led by Stern. Attempts to discredit them and Stern with statements such as “they never discovered a planet” are nothing more than cheap shot ad hominem attacks. These are the type of tactics used by those who cannot respond to the issues and instead attack the people making the arguments. Stern, a respected scientist, does not stand to lose anything personally, as New Horizons is already launched, and its findings will very likely receive worldwide attention regardless of what Pluto is called. However, as a planetary scientist whose specialty is Pluto and the Kuiper Belt, he is in a far better position to analyze these objects than astronomers who study other phenonmena such as black holes, cosmology, quasars, etc. The same is true for the many other planetary scientists who are not members of the IAU but whose views were ignored in the IAU’s decision making process.

And that process was undemocratic, closed, and in StevoR’s words, disgraceful. What sort of scientific organization does not allow for electronic voting? Watch the planet definition session, which is on the IAU web site, to see what was essentially theater of the absurd–last minute changes that confused even those who did vote, continued attempts to get to a vote without answering serious questions from astronomers, lack of clarity over the terms of individual resolutions, and on and on. The recent plutoid decision was even worse, with major astronomers including Mike Brown never even informed that this was in the works.

This issue could largely be resolved with acceptance by the IAU that dwarf planets constitute a subclass of planets.

I intend to be at the Great Planet Debate and will blog from there on my web site at http://laurele.livejournal.com . This event is open to the public, and I encourage all who are interested to consider attending.