Heavenly body count

A science textbook conventionally starts by laying scientific groundwork and then logically building its topic. This works when the topic has matured to a stage where it is understood - and has perhaps started to lose excitement.

What does a textbook author do about a topic that is still developing? Not teach the topic, perhaps? But the demand by students to learn about an immature topic that is important, stimulating and attractive may be compelling. This is true of planetary science. The space exploration of our own solar system has amassed scientific data about its nine (or eight) planets, 60 natural satellites and tens of thousands of smaller bodies, including the newly identified frozen worlds of the Edgeworth-Kuiper Belt, beyond and perhaps including Pluto. The scientific faces of these worlds are as individual as our own, and planetary science, like anthropology, is about the similarities and distinctions.

Planetary science is also about how planets came to be as they are. In the past five years, 100 extrasolar planetary systems have been identified, all members of different families of planetary systems; one could say as different from a collection of humans as a collection of gorillas.

George Cole and Michael Woolfson have written their textbook on a rapidly developing topic in an interesting way. They provide an assemblage of relevant scientific material with which it is possible to address specific facets of the topic. The parallel that sprang to mind was Max Born's well-loved book on atomic physics, written around 1935 when quantum mechanics was new.

Cole and Woolfson's textbook is for senior undergraduate and PhD student use. Its first third is a multidisciplinary account of planetary systems, grouped by bodies of similar type. The style is admirably economical. These chapters have appropriate illustrations, but their quality leaves something to be desired. Some of them were originally in colour and are now washed-out grey. In others there is moire fringing between two pixellating processes. There is a too-small four-page plate section of eight colour illustrations, two of which (Pluto and a false colour shot of Saturn's rings) are a waste of the colour opportunity. Although there are terabytes of excellent relevant illustrations on the worldwide web, the book makes no reference to the internet.

Two-thirds of the book is taken up with 41 scientific topics, each with related problems for the student. Topics include statistical and celestial mechanics (virial theorem, commensurate orbits), planetary structure (geochronology, tides), magnetophysics (planetary magnetism), planetary formation (Eddington accretion, heating by accretion) and planetary system evolution (migration of orbits, interaction in a cluster). These topics are all well developed at a mathematical level.

Cole and Woolfson's book will enable the planetary science course teacher at university flexibly to build his or her own syllabus, according to his or her and the students' interests and the excitement of the moment.

Paul Murdin is a senior fellow, Institute of Astronomy, University of Cambridge.