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:
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.