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Debate rages on about whether Pluto should be classified as a planet

By Lauren Gilger
Published: Tuesday, March 19, 2024 - 12:03pm
Updated: Tuesday, March 19, 2024 - 12:04pm

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Pluto
NASA
Pluto.

Pluto was discovered here at Lowell Observatory in Flagstaff. And there was a bill this session at the Arizona Capitol to designate Pluto the official state planet, even though its planetary status though was downgraded to dwarf planet in 2006.

Apparently there is still debate over whether or not Pluto should be considered a planet.

National Geographic writer Eric Alt recently spoke with two scientists on either side of this debate: pro-Pluto astronomer Philip Metzger and "How I Killed Pluto and Why It Had It Coming" author and astronomer Mike Brown.

Alt spoke more with The Show about the debate and the future of Pluto.

Full interview

ERIC ALT: It's something that has been sort of a, a kernel of debate for some time. A lot of it has to do with the IAU, the International Astronomical Union, sort of developing a criteria for what defines a planet. And that kind of came obviously much, much later than the discovery of Pluto, which was in the 1930s. And that kind of had people sort of retroactively look back and go well, this is the criteria for a planet, then Pluto doesn't actually fall into this category. It's not actually a planet. So it seems like it's something where it's been something of a debate within the community for really quite some time as they discovered new planets, new bodies, there was a planet called Eris that potentially could have been one, and then it ended up being not quite able to designate as a planet. So I think there were sort of new discoveries of the last 20-30 years that sort of put into question, you know, what is a planet? And it kind of centered around Pluto because Pluto sort of became the most famous case, right?

LAUREN GILGER: So there's this argument that they bring up that like because of, you know, dwarf planets, these other objects out there in the distant reaches of our solar system, like Pluto, like, if we were to consider Pluto a planet, we would also have to consider like hundreds of other objects out there planets. Is that right?

ALT: Yes. Yeah. I mean, there could be infinite number. I mean, there could be as many as 200 planets in our solar system. Which, which is funny because I think a lot of people, because like, a lot of people grow up making the little sort of, you know, foam ball solar systems when they're in elementary school. And it's like, there's a nice symmetry to it. There's, you know, eight or nine, it's kind of a nice round number. But it, it's like, yeah, it could be as many as 200 I think there's, there's, I don't know if there's a need to really limit it, but it just seems like there's a nice, kind of like, it's easier to wrap your head around, you know, a set number of planets as opposed to like an infinite number.

GILGER: Yeah. And as a, as a parent of little kids, I can tell you, you know, infinite kids books about the planets. Right.

ALT: You know, it's funny. I actually just the other day was in a CVS and they had, you know, a kid’s, it was like, they were little chalk balls that were to represent all the planets. It was like a solar system, chalk ball. And they had Pluto in there they had in parentheses, dwarf planet. So it's like they still want to include it. They still love to have it in there, but they just quite can't let go of it.

GILGER: That's so funny. It's true. We cannot let go of Pluto. OK. So I want to hear about the other side of this, right? Like you're talking to these two experts. I didn't even realize they're sort of an anti-Pluto contingent in the science world and then a pro-Pluto contingency. What are the pro-Pluto people saying here? What's their argument for the fact that it should still be a planet?

ALT: Well, one of the, one of the funniest things that and this came from Mike Brown who was on the anti-Pluto side of things, he also clarified that it's not a huge, huge divide in the science community. There are, there are very vocal factions but it's not like there's a huge division, but there are, there is a small faction that's very pro-Pluto. And he suspects that the reason is, is that most of those people were involved in the 2006 New Horizons program, which where they, they sent a vessel up to Pluto and they were all so deeply involved and a lot of them, a lot of them were upset because by the time the vessel came back, Pluto was no longer a planet. So it was like it was a planet when they left, but it wasn't a planet when they came back and I think they kind of wanna fight for sort of the relevance of that, that program. So I think that's, that's part of it.

I also think from talking to Philip Metzger, who's on the pro-Pluto side, he thinks that the, basically the criteria that the, the IAU came up with is just, doesn't take into account a lot of other factors. And one of the most interesting things that he said was, in fact, they were really surprised at how, how diverse the planetary makeup of Pluto is. And as a matter of fact, it's one of the more earthlike planets in terms of having its geography is so diverse and its atmosphere. And it actually has a lot of the elements that make it one of the most earth-like planets. So I think there's, there's a sense of like not, not holding it to such a strict criteria. I think it, I think it allows it to kind of make its case that it really should be among the, the main, I guess you could call the main planets. But one of the, one of the funniest things that, that Phillip said in the interview was that even though their name is the International Astronomical Union, they are very adverse to astronomical numbers. They don't, they don't want endless numbers of planets. They want a very tight group of planets.

GILGER: OK. So there's also this idea of an actual like and yet undiscovered ninth planet out there. Right? That's been discussed quite a bit in these circles. What's that about and how does that kind of play into this debate?

ALT: Yeah. No, that, that's very true. Mike, Mike Brown has been very involved in, in that, in what they're called planet nine or the ninth planet. They're constantly searching because one of the things that he said was that, you know, obviously technology has improved by leaps and bounds even within the last 20 years. I mean, we see it. He used the analogy of a digital camera. I mean, we were all excited by like, you know, 400 pixels early on. But now you've got, you know, extreme high-def and extreme quality and that has really helped that community explore an infinite number of potential planets or at least planetoids or, or celestial objects. So they are finding evidence of this planet by tracing, you know, orbits of surrounding bodies and things like that. But they have haven't actually quite found the planet yet, but there's enough evidence to suggest something is there. They just need to really hone in and pinpoint where it is.

GILGER: Just gives you an idea of how big space is. Yeah.

ALT: Yeah. And it's funny to think that you could have all this evidence of something, but you still can't quite see it.

GILGER: So I wonder then after having talked to both of these people who are experts on both sides, what do you think like are you on the pro-Pluto side or do you think it's really not a planet?

ALT: I will say I did a complete 180. I came in, I was of the mind that now Pluto shouldn't be a planet. I kind of was like, oh, you know, I think it's true. I think, you know, when it was discovered it was, you know, the, the technology was still so limited and, and I think people were just excited by the idea of a new planet and kind of jumped on it. So I was, I was ready to be very anti-Pluto. But I have to say hearing Phillip's arguments about that, you know, the atmosphere, the geography, how, how the criteria doesn't quite match up with some of the other accepted planets. He won me over, I think he won me over. I think I'm gonna be pro-Pluto now.

GILGER: All right. All right. Pro-Pluto there. This is Eric Alt, National Geographic contributing writer, here to tell us more about this apparently ongoing debate. Eric, thank you so much for coming on and explaining this. I really appreciate it.

ALT: Thank you for having me.

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