Astronomy and space travel has always fascinated me and recently I found an equally fascinating book on Pluto and the whole debate out the definition of a planet. Perhaps that sounds like a dry, boring subject for some but The Case for Pluto is a book you won’t be able to put down. It’s fairly short, able to be read in three or four hours, but thoroughly introduces you to the changing view of our solar system.
Our present understanding of the universe reflects thousands of years of observations. Mercury, Venus, Mars, Jupiter, and Saturn are all visible to the naked eye. The only apparent difference between them and other stars was the fact that they ‘wander across the sky’. Thus we get the word planet, which is derived from the Greek word for wanderer. The discovery of a seventh planet, Uranus, didn’t occur till 1781 when telescopes allowed us to peer deeper into the night sky.
Something didn’t add up with Uranus, though: Its orbit wasn’t matching mathematical calculations, due to unknown gravitational effects from somewhere else. This led to predictions Neptune’s existence years before it was observed. This was an amazing feat, one that many would try to replicate. However, Neptune solved all the problems and there wasn’t any solid mathematical evidence to base another planet prediction. Nevertheless, some persisted in searching for the next planet. That’s why Pluto was found.
Pluto was clearly a misfit but it was accepted into the special category that we call a planet. It wasn’t till the discovery of Eris in 2003, slightly larger than Pluto but much further away, that the IAU considered it urgent to define a planet. The Case for Pluto argues their controversial resolution was a hasty decision that may need some more thinking. Though the title led me to believe the book would argue forcefully for retaining Pluto as a ‘regular’ planet as it was for three quarters of a century, it was quite fair and seemed to accept the idea that Pluto needs to be in a separate class of planets, like the four gas giants and the four terrestrial planets are. I agree- we don’t need to ‘downgrade’ Pluto, but create a new class for it and its more distant relatives.
About the author: Alan Boyle is a journalist, serving as the MSMBC science editor since 1996. The Case for Pluto is his first book.