Is Pluto a Planet? by David A. Weintraub

Here's a non-fiction book that I picked up from the library. This is a good example of the typical book I would have read at one point in my life. However, in the past 9 or so years, I've been reading more fiction than non-fiction.

Is Pluto a Planet? is subtitled "A Historical Journey through the Solar System". The subtitle is fitting. A good part of the book covers a history of man's understanding of the solar system, from pre-Aristotelian days to the present. For example, in its earliest form, the 7 planets were the sun, the moon, Mercury, Venus, Mars, Jupiter and Saturn. In addition to those first two, which might sound odd today, note that the Earth isn't one of them. As man's understanding of the solar system improved, in addition to adding Uranus and Neptune to the list of planets, the Earth was added and the sun and moon removed. Interestingly, there no less than 15 other objects that were at one point considered planets by a sizable segment of the scientific community. These were the 4 Galilean moons of Jupiter, the 5 largest moons of Saturn, the first 4 asteroids discovered (Ceres, Pallas, Juno, and Vesta), and also Vulcan and Hind's Planet (which doesn't seem to have a large web presence).

Then there's Pluto, which was the fourth object to be considered the 9th planet, and is a focal point in another redefinition of the word "planet".

The book has its good and bad points. On the plus side, in addition to what I've mentioned, it traced the history to the present, including a section on the Kuiper Belt, which was discovered after I finished school. On the down side, there are sections where the discoveries of several Kuiper Belt and Scattered Disk Objects are boringly described in paragraph form.

Also, the author seems to feel strongly about his opinion. He's looking for a physics-based definition of the word "planet", and if I understood him correctly, he feels that it should be any object that isn't, wasn't, and won't be a star, and is large enough that its shape is primarily determined by hydrostatic equilibrium (is mostly spherical). In real terms, how does anything larger than Miranda sound*? (That is, a diameter of about 500 km.)

In being a scientist looking for a physics-based definition, he is forgetting any historical basis for the word, so I'm not sure I agree with him. It seems like we need a new word, but as we learn more, there will always be borderline cases. For example, Chiron was originally thought to be an asteroid when it was discovered in 1977, but now it's also considered to be a comet.

All-in-all, it's not bad, but not something I'd recommend to someone who's not interested in astronomy. For the general reading population, I give it two stars out of five.

* See mirandasound.com.