2019, Book 32: How I Killed Pluto by Mike Brown

Book 27: Black Hole Blues by Janna Levin. I guess I should expect privilege in academia.  Still sucks.

Book 28: What Belongs to You by Garth Greenwell. Not exactly my taste, but great writing.

Book 29: The Big One by Jack Page and Charles Officer. In almost all science, more data is better. Seismology is a concrete example most people can viscerally relate to.

Book 30: Passing by Nella Larson. Certainly got me to thinking about things I never thought about before.

Book 31: Our Mathematical Universe by Max Tegmark. Perhaps just me, but a lot of the implied profundity didn't land.

Book 32: How I Killed Pluto by Mike Brown

Of all the controversies in science, I would never have expected the classification of an inanimate object to evoke the emotion that Pluto no longer being considered a "planet" has.  More than once, someone asking me "Why isn't Pluto a planet anymore?" (I'm the resident expert in some of my circles on such matters apparently) was stopped in their tracks with the simple counter "Why should it be a planet?"  Occasionally, confusion is brought up or Pluto's lengthy tenure in the planet club comes up or some other excuse that is, at its core, emotional.  However, once those are dispensed with, the very difficult task of defining what a planet is becomes apparent.  Too loose a definition will include comets and asteroids and too tight a definition might leave out Mercury or Mars.

This is not to say all attempts at re-re-classifying Pluto as a planet are emotional.  Many prominent astronomers are throwing their full weight behind efforts based on quantifiable criteria, chief amongst the astronomers I follow being Alan Stern, Principal Investigator for the New Horizons mission to ... (any guesses?) ... Pluto.  I honestly haven't followed the debate closely and don't have a strong opinion.  However, I will say that after reading Mike Brown's logic, the astronomers trying to re-re-classify Pluto will have their work cut out for them.

Brown's logic goes something like this.  If an alien spaceship with senses and technology similar to our's were to approach our sun, how would they see things?  A few details aside, the approach would go something like this.  At first, only the sun itself would be a faint speck, all else too small and even fainter.  As the ship approaches, in a relatively short span of travel, all the gas giants would become bright enough to detect.  There would then be a lull in any new bodies that could be detected.  Then in another relatively short span, the rocky inner planets would be detected.  There would then be another lull before the asteroid belt and Kuiper Belt (where Pluto resides) would be detectable.  Mike Brown makes the case that the classification based on these detectability lulls makes for a more enlightening means of distinguishing the bodies than the old way; and, as far as I know, Brown still believes today that this is a better system than any current proposal that makes Pluto a planet again.

As noted above, this logic not only can be challenged, but is being challenged.  I will leave it to the actual astronomers to hash this out.  All I can say is Brown's logic makes sense to me.  My suspicion is it will break down somewhere in the distant future when hard definitions for "exoplanet" are needed and all proposed definitions will first be applied to our home planetary system.  I would hope enough data is available by then to extract some useful patterns for use.  Until then, I will continue to glance at the debate occasionally, but am quite satisfied to not call Pluto a planet.

I really liked that Brown wove some personal notes into this narrative.  I've been lucky enough to meet Brown in person and he's always come off as a thoughtful, caring person who lets out an occasional public zing like "They thought George wasn't a distinguished enough name for a planet, so they called it Uranus."  While the chapters in this book didn't quite alternate between planetary science and his personal life, I thought his autobiographical bits did a good job of communicating who he is to the reader.  This is the main reason this book stands out amongst popular science books.