Pluto – Sentinel of the Outer Solar System Author: Barrie W Jones Publisher: Cambridge University Press ISBN: 978-0-521-19436-5 Price: £25 (Hb) 231pp
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As far as name changes go, Pluto’s re-branding as the largest ‘plutoid’ has been rather unsuccessful in that no-one quite understands the lengthy criteria defining planets from plutoids from dwarf planets.All this, when combined with the enormous distance between us and Pluto, means this little world orbits at the very edge of most people’s understanding.My confusion on the subject continued as the book referred to Pluto as a planet on a number of occasions, however it is Pluto that is really interesting and not what we happen to categorise it as.

Pluto: Sentinel of the Outer Solar System is very well suited to someone coming to the subject without much prior knowledge. It clearly explains the formation of Pluto and the Edgeworth-Kuiper Belt of which it is part. I was fascinated to learn that if you clumped all the small icy objects in this region (including Pluto) together they would make up just one–tenth of Earth’s mass; yet 4.5 billion years ago these objects would have totalled between 15 and 50 times the mass of Earth! The book also thoroughly covers the discovery of Pluto along with the discoveries of Uranus, Neptune, Pluto’s moons and the Edgeworth–Kuiper Belt Objects.

Readers with a greater understanding of mathematics can find more detailed explanations in the many separate boxes while the rest of the text is easily accessible to a wider readership. Everything we currently know about the surfaces and interiors of Pluto and its moons Charon, Nix and Hydra is described. I was intrigued that simply by timing how long it took Charon to pass in front of a distant star we have learned that a seven kilometre deep depression exists on its limb! The penultimate chapter is dedicated to the New Horizons mission that will fly past Pluto and its odd little icy family in 2015.

In the end, whatever you call it. Pluto is a fascinating and important object and despite its vast distance this book will seem to bring it far closer.

David Powell