Friday Sprog Blogging: revisiting Pluto.

There's been a continuing discussion, in various online venues (including this blog), of Unscientific America, a book which notes the "demotion" of Pluto as an instance where the lessons the American public drew from the scientists' decisions may have diverged widely from the lessons the scientists would want the public to draw -- if they even thought about the possibility that the public was paying attention.

So, since the Free-Ride offspring were paying attention as the Pluto saga unfolded, I thought I should double back and see what their current thinking about it is.

If you've forgotten where they stood at the time, here are the relevant posts:

Friday Sprog Blogging: scientific controversy at the breakfast table

Friday Sprog Blogging: in which hermetic knowledge is revealed and a scientific disagreement is resolved.

Friday Sprog Blogging: Pluto update

Looking for the appropriate rhyme for "twelve".

Friday Sprog Blogging: a song with secret science content?

Dr. Free-Ride: So, you guys remember what happened to Pluto?

Younger offspring: Pluto used to count as a planet but now it's a dwarf planet.

Dr. Free-Ride: Yeah. Do you remember why the International Astronomical Union made that decision?

Younger offspring: Because Pluto is really small.

Elder offspring: And because its orbit was elliptical rather than circular --

Dr. Free-Ride: You know, the orbits of the other planets are elliptical, too. But you're right, the other orbits look more like circles, and Pluto's is more obviously an ellipse.

I showed great restraint here. I did not lead the sprogs on a detour about how a circle is a special case of an ellipse. Conic sections were not on our agenda. At least not this morning.

Elder offspring: Also, Pluto's orbit crosses Neptune's orbit, and they decided that planets have to be able to "clear their orbits" or something like that.

Dr. Free-Ride: Can you think back to when the IAU made the decision to reclassify Pluto and try to remember how you felt about it?

Younger offspring: If Pluto were a person with feelings, I would be mad, and I would have been mad at the scientists for siding with the bigger planets.

Dr. Free-Ride: But since Pluto isn't a person with feelings?

Younger offspring: It's fine.

Elder offspring: I don't think I was happy or sad about it. It was just something interesting.

Dr. Free-Ride: Did you guys realize that before the whole Pluto thing, astronomers actually didn't have a very clear definition of what counts as a planet?

Younger offspring: No.

Dr. Free-Ride: I guess they just kind of figured there was a pretty small number of them in our solar system, so here it was enough just to list them. If it went around the sun in a regular orbit and it was a big enough hunk of rock --

Elder offspring: --or ball or gas, or hunk of ice --

Younger offspring: Then it was a planet.

Dr. Free-Ride: Do you remember what started messing things up for Pluto's status as a planet?

Elder offspring: When they found that other one, Xena, that was about the same size as Pluto.

Dr. Free-Ride: Yep. Astronomers found more stuff out there in our solar system that was similar enough to Pluto that they had to decide ...

Elder offspring: Were they all planets, or were none of them planets?

Younger offspring: Even Pluto.

Dr. Free-Ride: Yep. By the way, the dwarf planet they used to call Xena is now called Eris.

Elder offspring: That's the name of the Greek spirit of strife. Are the astronomers trying to say it's her fault, not theirs, that Pluto isn't a planet anymore?

Dr. Free-Ride: Hmmm. That may be. So do you guys think the astronomers made a reasonable choice in how they defined classical planets and dwarf planets.

Younger offspring: Sure.

Dr. Free-Ride: Do you think they could have decided on a different definition of planets than the one they ended up with?

Elder offspring: Yeah, why not?

Dr. Free-Ride: So you both are totally comfortable with the idea that the definitions are to help the scientists, and that they deal with the characteristics humans think it's useful to use in describing different kinds of stuff.

Elder offspring: Uh huh. There's lots of categories scientists define.

Younger offspring: Plants, animals, fungus.

Elder offspring: Mammals, canines, domestic canines.

Younger offspring: Fruits, vegetables, healthy foods, snack foods.

Dr. Free-Ride: I'm not sure all of those categories are strictly scientific, but OK. Did the whole Pluto demotion surprise you when it happened?

Elder offspring: Not really. Science is always learning new stuff.

Younger offspring: Pluto wasn't new.

Elder offspring: But we didn't know about Eris before -- that was new. And scientists wanted to think about how the old stuff and the new stuff fit together.

Younger offspring: OK.

Dr. Free-Ride: Did the Pluto affair make you more interested in learning about astronomy?

Elder offspring: No. But I was already interested in it.

Younger offspring: Not really. But The Hitchhiker's Guide to the Galaxy makes me more interested in learning about astronomy.

Elder offspring: I would be more interested if we knew how to travel at the speed of light. Otherwise, it would take too long for me to get to other galaxies.

Dr. Free-Ride: And you have other stuff to do with your time?

Elder offspring: Yeah.

More like this

It seems the IAU ruling on what counts as a planet has stirred a little controversy in the Free-Ride home. Dr. Free-Ride: You heard what happened with Pluto, right? Younger offspring: It's not there any more. Dr. Free-Ride: Uh, it's still there, just as big as it was and pretty much where it was…
This week, in SprogCast #4, the younger Free-Ride offspring sings and then suggests that the song bears on the planetary subject of the very first Friday Sprog Blogging entry, which also involved singing. You can download the sound file for the a cappella performance and the discussion that follows…
(Based on actual events.) Younger offspring (age 4.5): (singing softly to self while arranging a line of nine grapes on breakfast plate) Nine planets, fine planets, in our solar system. Nine planets, fine planets, go ahead and list 'em ... * Elder offspring (age 6.5): You know, in school we…
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You do an amazing job teaching your sprogs, Janet. That was a great discussion.

By Dave Gill (not verified) on 17 Jul 2009 #permalink

The Hitchhiker's Guide to the Galaxy makes me more interested in learning about astronomy.

Woot to the Younger Offspring!

There are several problems here. First, the International Astronomical Union did not make this decision--only four percent of its membership did, most of whom are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA's New Horizons mission to Pluto. Since there clearly is no consensus among astronomers on a definition of planet to this day, it is not correct to say we finally have a planet definition. The reality is that we have an ongoing debate between dynamicists, who study the effects celestial objects have on one another, and planetary scientists, who study the geophysical composition of individual celestial objects.

One reason the IAU definition makes no sense is it says dwarf planets are not planets at all! That is like saying a grizzly bear is not a bear, and it is inconsistent with the use of the term âdwarfâ in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies. Also, the IAU definition classifies objects solely by where they are while ignoring what they are. If Earth were in Plutoâs orbit, according to the IAU definition, it would not be a planet either. A definition that takes the same object and makes it a planet in one location and not a planet in another is essentially useless. Pluto is a planet because it is spherical, meaning it is large enough to be pulled into a round shape by its own gravity--a state known as hydrostatic equilibrium and characteristic of planets, not of shapeless asteroids held together by chemical bonds. These reasons are why many astronomers, lay people, and educators are either ignoring the demotion entirely or working to get it overturned.

The better choice is that all objects that orbit the sun and are in hydrostatic equilibrium be considered planets. Dwarf planets should simply be a subclass of planets that are planets by virtue of being spherical but of the dwarf variety because they do not gravitationally dominate their orbits. I hope you share this perspective with your students because they deserve to know there are two sides to this debate.

Here's a rhetorical question: Why do you think the IAU waited until the last day of their conference (when most scientists had already left) to "vote" (and I use that word loosely) on the definition of a planet?

I just ignore the IAU definition. If something is just blatantly wrong, should it be considered "right" just because the IAU said it?

Pluto is a planet regardless of the peremptory command of the IAU!

Not really. But The Hitchhiker's Guide to the Galaxy makes me more interested in learning about astronomy

That's just awesome.

I always bemoan that kids today don't know the classics; I'm glad that your younger offspring does.

re Laurel:

Of course most members of the IAU didn't vote---most members are not planetary scientists, so it's outside their area of expertise.

I'm not saying that the right people voted, or particularly defending the way they voted; I just think it's ridiculous to act as though this sort of thing should be decided in a straight democratic fashion, even among astronomers, much less members of the general public.

Any non-planetary astronomer or non-astronomer who thinks this is a big deal needs to get a freaking life.

As far as the general public goes, it's mostly an opportunity to learn about the issues, and why astronomers might disagree---or just to joke about something that makes no difference.

One position that's definitely wrong is Mooney and Kirshenbaum's---nostalgia- and popularity-driven distinctions are stupid. They seem to miss the fact that much of the attention to Pluto is wryly making fun of people like them who get the vapors over nothing.

Elder offspring: That's the name of the Greek spirit of strife. Are the astronomers trying to say it's her fault, not theirs, that Pluto isn't a planet anymore?

Not that I'm gonna have kids, but if I were, I'd like them to be this kind of wisearses.

"Of course most members of the IAU didn't vote---most members are not planetary scientists, so it's outside their area of expertise."

This is not correct. The reason only four percent of the IAU voted on this was because the vote was held on the last day of a two-week conference, and no absentee voting was allowed. Most IAU members who did attend had left by the time the vote was taken. And most who voted are not planetary scientists but other types of astronomers. Conversely, a large portion of the professional astronomers who signed the petition opposing the IAU definition are planetary scientists.