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Pluto: Sentinel of the outer solar system , by Barrie W. Jones . Cambridge, UK : Cambridge University Press , 2010 , 244 p. $35.99, hardback (ISBN #9780521194365 ).

Barrie Jones, a widely read popularizer of astronomy in the UK, has presented in this book a friendly introduction to the state of our knowledge of Pluto. It’s quite a pleasant read, if somewhat elementary … and at times frustrating for not going a step or two further down the many interesting paths he opens up.

His topics include a brief history of the discoveries of Uranus and Neptune before treating the development of the logic behind the search for Pluto. It is wonderful to have, in one setting, a description of the detailed predictions made not only by Percival Lowell but also by his chief rival in Planet X prognostications, William Henry Pickering. He includes, in passing, an admirable introduction to many of the techniques used by planetary scientists to understand what a planet is like, and how it may have gotten that way. These include short set-aside boxes where the elementary calculations involved in this work (nothing more elaborate than algebra) are worked out.

After discussing how our understanding of Pluto has evolved since its discovery, he also presents a description of the Pluto family of moons (as known only up to 2010). A further chapter discusses the Edgeworth-Kuiper Belt where Pluto resides. The last three chapters are brief discussions of Pluto’s status as a planet, the upcoming New Horizons mission, and a fun (if much too brief) discussion of the possible role that Pluto might play in the far distant future of human space travel.

Jones, admirably, includes the names (and often the photographs!) of the scientists who have done this work. For those of us in the field, it is nice to see our colleagues recognized, while even a casual reader can see familiar names recurring, and thus recognize the players in the relatively small community of researchers studying Pluto.

All this is presented in a style that gives the feel of a friendly uncle telling stories over coffee at the dinner table. It is a most relaxing and enjoyable read.

That said, there are two serious questions about this book that need to be addressed. First, who is the audience that this book will most likely appeal to? And second, why was this book written now, a mere 5 years before the New Horizons mission arrives at Pluto?

Though it is clear that Jones has done his homework, this is by no means a scholarly text. There is a chapter-by-chapter listing of further readings and resources; he’s clearly familiar with the literature. But no original work is presented here, and in keeping with its friendly tone there are no footnotes or even indications of whether the sources he is relying on are primary or secondary. In areas that are controversial, like the history of the discovery of Neptune where many aspects of priority and national pride are hotly debated, it is hard to judge his telling of the story without knowing his sources.

His inclusion of the names and photos of current researchers is well and good, but there are none of the personal descriptions that an insider might tell. Dale Cruikshank, Dave Tholen, Alan Stern, Fran Bagenal, Elliot Young, Dave Jewitt, Jane Luu … these are my friends, I have known them all for 30 years or more; and it’s especially delightful to see included the important early work of Leif Andersson, who died much too young, just as modern Pluto studies were getting started. I can’t see their photos here without thinking of their lively personalities, and all the funny personal stories one could tell about each of them. Surely, someone researching a book on Pluto could have taken a vacation to Boulder or Hawaii to drop in on them, or at least arranged to meet some of them at a DPS meeting? Maybe Jones did; I don’t know. Alas, his text itself shows no evidence of ever actually having met any of them in person.

Jones’s status as an outside observer is most evident in his chapter on Pluto’s status as a planet. Regardless of how one feels on the topic (I’ve passionately argued both sides, at one time or another!) this is a topic that provides a great opportunity to teach how science classifies, and what the deeper issues are behind the controversy. Jones’s chapter is especially frustrating because he does recognize this opportunity, but after a promising start his discussion peters out without really developing anything new. His review of the process and the arguments involved is superficial at best. He offers no insight as to why the IAU came to its decision, nor even why it felt it needed to make such a decision at that particular time.

Most puzzling of all, however, is the chapter on the New Horizons mission … not because it’s there, but because the very fact of this mission suggests this whole book itself will be hopelessly out of date in less than 10 years. So why was this book written now?

The best argument for the existence of this book is in fact that it provides a very good preparation for understanding the New Horizons mission when it arrives at Pluto. That being the case, one might have expected New Horizons to be introduced at the beginning, not the end, providing a constant theme throughout the book. Instead, this mission is presented almost as an afterthought.

Do I recommend this book to the readers of MAPS? It is not a reference text, and not one that a research library needs to spend its resources on. But it is a very friendly introduction, one that I hope the journalists covering New Horizons will be familiar with once the spacecraft arrives at Pluto. Perhaps Cambridge University Press will prepare a new, updated edition at that time.

In the meantime, this book strikes me as a perfect gift for a young teenager with an interest in space. The math is certainly within the grasp of any science-literate high school student. And the background discussions are a good introduction to not only what we know about the solar system but also how we know it.