Dr. Alan Boyle twittered notes from the entire discussion, which he put together on the following site: http://family.boyle.net/plutonotes.htm . I encourage anyone interested in this debate to read these.
In a column written after the conference, which can be found here, http://cosmiclog.msnbc.msn.com/archive/2
It is interesting that of all speakers, Tyson is the one who makes this comment, as he is the one who re-energized this debate in the first place when he chose to design the solar system display at the American Museum of Natural History's Rose Center with only eight planets. He has done speaking tours as well as radio and TV interviews on this subject. He wrote an entire book on it. But suddenly, he decides it's time to move on? What gives?
In response to Tyson, Alan Stern, as quoted by Boyle, emphasizes that the way we think of planets should reflect the diversity of the solar system. Objects like Pluto make up the largest class of solar system planets, he notes.
An important aspect of diversity is the concept that many very different items can be encompassed in a broad category. Just think of the terms "plant" or "animal," and this is obvious. Why then, do some insist that there can be only two classes of planets, the terrestrials and the jovians? If we artificially limit our definitions that way, we will be forced to create "wastebasket categories" to accommodate the objects that do not fit our narrow proscriptions.
"Moving on" from a bad decision such as the IAU planet definition by letting that decision stand is a terrible idea and makes no sense. The fact that this issue continues to be debated illustrates that the IAU decision satisfied few people and created tremendous confusion.
Jean-Luc Margot of the University of California at Los Angeles proposed sticking to the IAU definition but defining all round objects, whether they are gravitationally dominant or not, whether they are moons, planets, or dwarf planets, as "worlds." Using this concept," some worlds are planets, and others are not," he said.
Margot's approach does not really offer much that is new. By sticking with the IAU definition and then adding the term worlds plus the caveat "some worlds are planets, and some are not," he puts us right back at the problematic point we started from--the fact that the IAU definition classifies objects by where they are while ignoring what they are. If we're going to stick with the term planet, why not just come up with more adjectives to describe the many different types of planets we are discovering? Satellites like Titan and Ganymede can be referred to as "secondary planets" since their primary orbit is around another planet, and their secondary orbit is around the sun.
It is interesting to note that Mike Brown said he tries to avoid the discussion of whether or not Pluto should be classified as a planet altogether. He was for these small round objects being classed as planets before he was against it, and his blog title, "Mike Brown's Planets: Full and Dwarf" implies he considers dwarf planets a type of planet, which contradicts the IAU definition he now claims to support. Maybe he doesn't want to discuss the subject because he isn't sure which position he is taking on any particular day!
The opinions expressed at this conference reflect similar views expressed online covering the full spectrum of this debate. I am going to print one comment, written in response to a comment by me in the journal Nature in response to a June 3, 2009 article, "Quaternary Geologists Win Timescale Vote." The author sought to use the Pluto issue to illustrate an example of scientists reaching consensus, saying, "In 2006, astronomers reached a decision on the planetary status of Pluto; now, geologists may have done the same for the status of the Quaternary, the time period in which humans evolved and live today." The site is here: http://www.nature.com/news/2009/090603/f
When, in the comments section, I pointed out that saying "astronomers" reached a consensus on the status of Pluto is incorrect and disingenuous (given that, clearly, a consensus has not been reached), one respondent accused what he called the "Pluto is a planet gang" of hijacking the entire thread! Here is what he said:
"Incredible to see the Pluto-is-a-planet (because it was discovered by an American) gang highjack (sic) this item. Please, people, get over it! The decision has been made by the acknowledged international organisation (sic) in question. Feel unhappy about that? Your problem only! And don't come with that crap again about 'only a minority voted.' Only a minority seemed to be really interested to come to the vote. If this was important to you, you should have been there and have voted yourself. Every IAU voting member could have voted if he/she wanted. And those 'many astronomers' and the public said to be opposing the vote result: this is almost solely an American phenomena. It has much to do with the fact that Pluto was the only of the former 'planets' discovered by an American. The anti-movement regarding the IAU decision doesn't have a strong international footing at all..."
Another commenter said, "The reclassification of Pluto, it seems, is an accepted part of the curriculum and new teaching materials have already been produced. These things happen. Scientists redraw old conclusions based on new evidence. I can't see how correcting an error, even if it means some level of relearning, is a bad thing.