How I Killed Pluto and Why It Had It Coming by Mike Brown


I’ve known about this book for a while, but the title put me off read­ing it. It sounds too smug to me, and while there are reas­ons for reclas­si­fy­ing Pluto I don’t think it’s some­thing astro­nomers could be smug about. Planet was not a term inven­ted by astro­nomers, it came from pop­u­lar cul­ture in the ancient world. I’m also wary of how use­ful a rigid defin­i­tion of planet is. The ter­restrial plan­ets are clearly not like the Gas Giants, and per­haps you could even dis­tin­guish between Gas Giants and Ice Giants. The defin­i­tion for dwarf planet is ter­rible, and how can a dwarf planet not be a planet. Finally Mike Brown dis­covered Xena, which he argued could be the tenth planet, but I can recall there were a rash of plan­ets dis­covered. Wasn’t Sedna sup­posed to be big­ger than Pluto too? Then there was Eris and Dynomia too. So I wasn’t expect­ing to read much bey­ond the first chapter.

So first up, I still think it’s a bad title. Not because it’s smug, but because the book is the oppos­ite. It’s warm, endear­ing and very human. The author is also extremely well-placed to write the book because there was indeed a rash of plan­ets dis­covered, and he was the guy who assembled the team respons­ible for them, includ­ing Quaoar, Sedna, Xena and the moon Gabrielle which are now offi­cially named Eris and Dysnomia. Basically if it’s a dis­tant body in the solar sys­tem that I’ve heard of, it’s likely that Mike Brown dis­covered it.

This could have so eas­ily been a book purely about number-crunching, pro­gram­ming and extremely faint dots on pho­to­graphic slides. He’s also included a lot about his fam­ily life, espe­cially the birth of his daugh­ter. A quick skim of the reviews on Amazon show that some people hate this. They have an opin­ion that Science is pure logic devoid of emo­tion. I blame Spock. In con­trast I think it’s very import­ant. It shows how sci­ence is a human activ­ity. The removal of Pluto from the plan­ets wasn’t done in isol­a­tion, it was part of a very human desire to explore.

The import­ance of humanity’s rela­tion­ship to plan­ets comes through very early. More or less straight away he points out that people recog­nised plan­ets long before they had pro­fes­sional astro­nomers. He also notices that there’s very little evid­ence of plan­et­shock the first time a planet was dis­covered since ancient times. If you’d asked me before I read this book I would have said it was Uranus that was the first planet dis­covered since antiquity in 1781. I would have been wrong.

Though plan­ets were so deeply embed­ded into many aspects of every­day life, there is no record­ing of the pub­lic reac­tion to the first and most sig­ni­fic­ant shock to the word planet. In the six­teenth cen­tury the idea began to spread that the sun, rather than the earth, was at the cen­ter of the uni­verse and that the earth and the plan­ets revolved around it. Suddenly, the wan­der­ers were in dis­ar­ray. Instead of the sun and the moon and the other plan­ets revolving around the earth, five of them (the plan­ets) went around one of them (the sun), while the sev­enth (the moon) went around the earth. The earth, like five of the wan­der­ers, also went around the sun.

Once you have a helio­centric sys­tem Earth has to be a planet. I’m kick­ing myself for not real­ising that. With hind­sight it’s obvi­ous, though you can see why the dis­cov­ery of Earth as a planet wasn’t a big trauma in itself. He also tackles the minor plan­ets like Ceres and Pallas and their quiet demo­tion into asteroids.

None of this is done with a sense of “how stu­pid people were for not know­ing this”. Instead I get a sense that Mike Brown believes that people were using the word planet in a way that was use­ful to them at the time. Likewise with more recent astro­nomers he’s happy to give credit to their work. Where he has been able to go fur­ther he’s acknow­ledged that he has had the bene­fit of liv­ing at a time with tech­niques like com­puter ana­lysis that weren’t avail­able to earlier astro­nomers. At one point he argues that Clyde Tombaugh could have seen Eris, were it not for Eris being at the far point of its orbit.

He also tackles the con­tro­versy over the dis­cov­ery of Haumea. At the time I got the vague impres­sion that a slow team of astro­nomers had missed a planet in their data and, when it was pub­licly released, another team ana­lysed the data and found it. Neither side of the dis­pute claim that’s what happened, so I was utterly wrong there. Mike Brown explains why he delayed announ­cing the dis­cov­ery of Haumea. At the top of the post I said Sedna was big­ger than Pluto. It isn’t. Its much more shiny, and that’s why it was thought to be big­ger. Mike Brown’s team were tak­ing nine months from dis­cov­ery to pub­lic­a­tion and it was when the code­name for the planet was released that it was dis­cov­er­able in a Google search on some tele­scope logs. This also explains why Xena was rush announced and partly my con­fu­sion over exactly what was and was not discovered.

The book closes with the vote in Prague to say there are eight plan­ets in the solar sys­tem. From what I heard of the meet­ing the event was chaotic, so he does an excel­lent job find­ing a nar­rat­ive to fol­low. It also explains the awful ‘dwarf planet’ term. The first vote was to demote Pluto to a ‘dwarf planet’ which is not a planet. It makes no sense until he then says there was an amend­ment to call the 8 plan­ets ‘clas­sical plan­ets’, which is another awful term. If that second vote had passed then Pluto would have been smuggled back as a planet. So the reason we have ‘dwarf plan­ets’ that are not plan­ets is a botched job at a compromise.

He also argues that the defin­i­tion of a planet itself doesn’t mat­ter that much. The defin­i­tion, he argues, isn’t about what is a planet, more an explan­a­tion of why Pluto isn’t a planet — even if it’s a bad explan­a­tion. Instead he argues that con­cepts are more import­ant rather than defin­i­tions that wan­nabe law­yers can wrestle with.

The lan­guage is access­ible. You’re not going to be able to dis­cover your own planet after read­ing this book, but you’ll have a bet­ter impres­sion of what life is like when research­ing. For example there’s this:

Looking at vastly more sky than any­one else had ever looked at for large objects out in the Kuiper belt was so immensely excit­ing that I could hardly con­tain myself. I knew that there would be big dis­cov­er­ies, and hav­ing new pic­tures come in night after night after night with only a break for the full moon kept everything at a con­stant peak. I talked to my friends about new plan­ets. I thought about names for new plan­ets. I gave lec­tures about the pos­sib­il­ity of new plan­ets. I did everything I could, except find new planets.

I think that fail­ure to make any pro­gress on what you’re sure is an excit­ing pro­ject is famil­iar to most researchers.

With the IAU’s poor hand­ling of Pluto, it’s easy to see how this could have been a dread­ful book. I still think the title is going to put a lot of people off. Is it really going to appeal to Plutophiles? That’s a shame because inside the cov­ers is one of the most like­able books I’ve read for a long while. It’s def­in­itely worth a read when the paper­back comes out.

You can read some of the book in excerpts at Mike Brown’s blog.