The Case for Pluto

The Case for Pluto is not settled yet, whatever the IAU may wish.
Now, just in time for the holidays, there is a very nice little book summarizing what happened in Prague that fateful summer.

I am decidedly "pro-Pluto".
Now Alan Boyle of the cosmic log blog, has taken up the baton, and written a very nice book to complement David Weintraub's Is Pluto a Planet.

"The Case for Pluto" is a very nice compact little book that is eminently readable.
Alan reviews the history of planet discovery and puts the Pluto controversy in context, with some interestingly frank interviews with many of the people involved.
The summary of the IAU discussion and how the issue came to be raised is concise but thorough, and consistent with what I heard. It is an object lesson in how committees of academics may not produce the outcome desired, and why transparency is generally good.
It also makes me ashamed to be a dynamicist.
Semantic arguments and over-pedantic insistence on consistency can get very tiresome.

The proposed resolution, and the broader picture of the exoplanet characterization problem is well presented, and makes sense. Although I think Alan may have missed the tension within the exoplanet community over how to define planets, and the current status of conforming to the definition for the Solar System.

The book is well footnoted, in fact I found in the references a citation I had been looking for! There is a nice central collection of good quality pictures, and the production is solid.

This is a very good book for someone who wants a quick summary of the history of the Pluto controversy and what actually happened in 2006, including my professional colleagues who were not paying attention. It would make a great christmas present for a mature pre-teen or teenager with interest in "space", and a good read for any amateur enthusiast. Did I mention it is nice and short?

Strongly recommended.

Title: The Case for Pluto
Author: Alan Boyle
Publisher: John Wiley & Sons
ISBN: 978-0-470-50544-1 (cloth)


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I'll certainly read it although I've never wavered from supporting Pluto as a planet. Ia Shub-Niggurath!

Compare Earth to Jupiter, Saturn, Neptune or Uranus. Now how can you justify considering Pluto an abnormal dwarf planet?

As for Eris, Xena (because I also recognise precendence in naming) & the rest - they're planets.

Bloody bigots.

Boyle's book is terrific! It's not too technical and does not require a prior background in astronomy to be understood. He also has a great section in the back of the book about what to tell kids regarding Pluto and dwarf planets. I am a writer, amateur astronomer and graduate student at Swinburne Astronomy Online who has spent more than three years actively advocating Pluto's reinstatement--and that of all dwarf planets. Boyle does such a good job making his arguments that I'm not sure what to put in the book about Pluto on which I am now working! For more on why Pluto is a planet and worldwide efforts opposing the demotion, visit my Pluto Blog at

Just to be contrarian, I don't think Pluto is a planet, but the definition of a planet is fraught with problems and ambiguity. Pluto is essentially like Ceres, in that it is the large scale end of a size distribution of planetesimals in the Kuiper belt. If Mike Brown and his telescopes lived near Clyde Tombaugh in space and time, Pluto would not have been elevated to the platform with the terrestrial planets, but called YAKBO (Yet Another Kuiper Belt Object)

I grew up with Pluto being planet, and watching as estimates of its diameter decreased consistently. (I remember reading a spoof paper that predicted that it would disappear entirely sometime in the late 1990s -- does anybody have the citation?). I sadly regret its demotion, but IIRC the committee's first attempt to include it as a planet required promoting a large number of other bodies (including Ceres), making the whole idea rather cumbersome (and the memorization task far more difficult). Pluto is (sigh) just a big KBO. (I am relieved, however, that the demotion came after the launch of the New Horizons probe, otherwise who knows what some bureacrat would have done.)

On my Christmas list (though I'd hesitate to call my pre-teen sensibilities 'mature'...).

The Weintraub book is odd, the way he (spoiler alert!) pulls out the hydrostatic definition without justification (and there is a justification, even if reasonable minds can differ over its value), and treats it as the only possible one. Result: much hilarity in the post-IAU appendix of the second edition, where he splutters apoplecticly. How he didn't at least see the possibility of it bemuses me.

I remember reading a spoof paper that predicted that [Pluto] would disappear entirely sometime in the late 1990s

I'm not familiar with that one, but the current issue of Annals of Improbable Research has an article predicting that the number of planets would go to zero in (IIRC--I don't have the article handy) 3700. The article takes the number of planets as a function of time and fits a third-order polynomial. The number of solar system objects considered planets has been higher than the canonical nine from my school days--originally Ceres et al. were considered planets.

By Eric Lund (not verified) on 11 Dec 2009 #permalink

As one who was there in Prague, I'm curious to read the book. I'm pro-Pluto; I just don't think it should be called a planet, for the reasons above.

By Craig Heinke (not verified) on 11 Dec 2009 #permalink

I'm with JohnD on this one. The definition is worded poorly, but Pluto shouldn't be regarded as a planet as it is a member of a belt of objects, as opposed to the major planets outmass everything else in their vicinity by several orders of magnitude.

Although the IAU definition of planet is only applicable to the solar system, the WGESP definition of "extrasolar planet" seems somewhat problematic too: there are several known systems out there which seem to strongly indicate that the deuterium fusion limit does not correspond to the high-mass end of the planetary distribution.

The IAU needs to come up with a better definition than the abortion they conceived in Prague and are trying to force upon the world, logic and scientific consensus be damned. If they need a scientific definition, as opposed to one rooted in tradition, which could have worked fine, they can go by mass; instead of a minimum diameter of 2000 kilometers like the IAU's own internal review committee had recommended, they could set a minimum mass, the one required for the object to achieve hydrostatic equilibrium. If that means hundreds of planets, well, Jupiter has more than 60 moons, and they're all still moons; if you can't recite all their names from memory and have to look some up, so what?