When Is a Planet Not a Planet? The Story of Pluto
By Elaine Scott
Clarion Books; $17.00
48 pp.; ISBN-13: 978-0618898329

Review by Amy Brozio-Andrews

If you were as unprepared to answer your kids' questions as I was when Pluto was suddenly demoted from planet-hood in 2006, you'll be glad to know that Elaine Scott's When Is a Planet Not a Planet? The Story of Pluto can fill in the gaps. In an attempt to explain how the solar system suddenly went from nine planets to eight, science writer Elaine Scott delves into the history of the planets orbiting our sun, getting into the specifics about the discovery and subsequent rejection of our formerly ninth planet Pluto.

Through a broad historical overview of astronomy, Scott demonstrates for young readers the process of building discovery on the work of scientists gone before, from Ptolemy, Copernicus and Galileo (proponents of the geocentric and heliocentric theories, respectively), to Kepler and Newton and their work on orbits and gravity to the current use of the scientific method for continuing advancement. Expanding the narrative into a brief history of our awareness of the solar system, Scott includes the discovery dates (and discoverers, where applicable) of the known planets.

It's when Scott wades into the "problems with Pluto" as she calls them that things get really interesting. Pointing out the similarities and differences between this outermost object and the eight nearer the sun, she juxtaposes it with the discovery of Ceres and Eris, two of the newest objects to fall under the scope of the "is it or isn't it a planet" debate.

Scott rounds out her book with an examination of the scientific community's work on defining planets, including the most recent meeting of the International Astronomical Union (IAU) in August 2006 that stripped Pluto of its status as a planet. Developing a three-part definition that left Pluto as a dwarf planet, Scott leaves open the possibility that continued scientific discussion and exploration may warrant the need for a revised definition of a planet in the future, one that may alter the line up from the sun yet again.

While perhaps not settling the discussion of Pluto as planet (isn't a dwarf planet still a planet?), she does quite satisfactorily secure for her readers an understanding of how and why science evolves and the study of planets in particular. Scott's easy writing style and clear definition of scientific terms and processes is engaging. Her inclusion of a glossary and list of related books and website for further study is encouraging. Spectacular photography, artwork, and artist renderings make the book visually interesting as well as topically interesting, making complex astronomical subjects understandable by a child without oversimplifying them.

Of course, now that we old parents have finally gotten used to the idea of Pluto not being a planet anymore (What will our very eager mothers serve us now?) and Scott's book has adequately explained to our kids what we might not have been able to, things might change again in the near future, quite possibly as early as this summer: the "Great Planet Debate" conference is scheduled to be held in August at Johns Hopkins University's Applied Physics Laboratory in Laurel, Maryland. Let's at least hope any future pronouncements come with a nifty mnemonic too, yes?