Thread by @bhgross144

Next Stern points out flaws w/@IAU_org definition of "planet." He notes that the IAU is made up primarily of stellar astronomers, and their definition does not reflect expertise of planetary scientists. (Again: key themes-disciplinary divisions, challenges of forming consensus)

Stern also notes that another rationale for the IAU definition of planet was limiting the number of planets for convenience. Suggests that this is a foolish rationale by pointing out what the IAU's periodic table might look like...

.@AlanStern backs a geophysical definition of "planet" that focuses only on an object's intrinsic attributes rather than their surroundings. Additionally, unlike the IAU definition, it applies to all planetary systems, not just our own solar system.

Stern concludes that scientists define many other things (e.g. species, geological formations, other astronomical objects) based on their own attributes, rather than criteria that are deliberately engineered to limit their number. Suggests IAU made a mistake by doing the latter.

Ekers steps up for a rebuttal. He agrees on the importance of expertise, but again distinguishes between the process of naming and the process of doing science.

[Again, I have to disagree with that framing-Forging an agreement on terms of debate is crucial to scientific inquiry]

Ekers also suggests that dynamicists have a much clearer definition of "clearing the orbit" than Stern implied. He also argues that the difference between the 8 planets and Kuiper Belt objects (which have no gravitational influence on anything else) is quite significant.

"Naming things is not the same as doing the science." -Ekers

(I wonder what he thinks about when he visits a natural history museum.)

.@AlanStern steps up to the microphone once again. He stresses that this isn't specifically a debate about Pluto. This is more broadly about what qualifies as a planet, and he points out some major issues with both the science and politics behind the IAU definition.

Stern cites work by @DrPhiltill, whose research shows that there have been no planetary science papers that embrace the IAU definition of "planet" while hundreds are using the geophysical definition. (Stern again points out that most planetary scientists are not IAU members.)

Stern concludes his rebuttal by suggesting that the press and science writers should respect both definitions, giving them equal space in textbooks, etc.

(This could be complicated...)

Opening up the floor to Q&A now. When this is finished, people can vote between Ekers (@IAU_org definition of planet) and @AlanStern (geophysical definition of a planet) by visiting @pswscience website: pswscience.org.

In response to question re: moons-Stern reiterates that the geophysical planet definition can encompass planets orbiting planets. (Again it's about the categories of the bodies themselves, which is why Ganymede, Triton, Io, etc are often referred to as planets in the literature.)

"I don't think the rest of the world would be comfortable with calling all these planetary satellites also 'planets.' If you want to call them planets in your specialized group, but I don't think the public would see that as a sensible answer." -Ekers

[Now I'm confused. Is Ekers arguing in favor of good Science (capital "S") or about what's sensible/understandable to the public?]

.@AlanStern draws parallels with other categories from the astronomical lexicon: "Dwarf stars are stars. Dwarf galaxies are galaxies. And dwarf planets should be planets."

Finally! Someone (Stern) points out how important categorization is in many different disciplines, as well as the centrality of consensus building around those categories in the scientific process. As he suggests, voting on a definition like this comes across as arbitrary.

Hey, @lizlandau is @pswscience! She asks Ekers & Stern how they envision the impact of their definitions of a planet on public understanding.

Ekers: It is important to understand split b/w 8 planets & Pluto
Stern: Big picture-3 classes of planet in our solar system & more beyond

Stern: The IAU will never be in a good position to get this right, because it's made up of people in a different field who are unqualified to comment on the subject.

Ekers: IAU is not about planetary science, but it is about international collaboration. Naming isn't science.

In addition to expertise, it appears that another pervasive theme in this debate involves the elegance of a definition. Both speakers have argued that their respective use of "planet" offers fewer potential contradictions or exceptions.

"There's not a right answer or a wrong answer. You need a consensus, and you need a vote." -Ekers' comment here provides the closest thing I think we've seen tonight for what distinguishes science & non-science.

And now, after an extended debate about the validity of a vote to determine the definition of "planet," it's time to go to pswscience.org and vote for a winner.

(The irony is palpable!)

Here's where things stand right now.

Ekers (@IAU_org definition of a planet) is marked in green.
@AlanStern (geophysical definition of a planet) is marked in blue.

It would seem that there's a clear winner.
(Presumably, the IAU, as a fan of referenda, will revisit the issue...)

It would seem that things are wrapping up with tonight's debate. Thanks to @pswscience for organizing this discussion, Ron Ekers and @AlanStern for fascinating talks, and everyone following this livetweet. (And thanks to @tracy_karin for bringing this livestream to my attention.)

(Oh, and before I forget, it turns out that @LindaHall_org has an extended run of the Bulletin of the @pswscience. If I have time tomorrow, I might take a look at Volume 1 from 1871, a copy of which is being given as a gift to the debate participants.)

lhall.hosted.exlibrisgroup.com/vwebv/holdings…