Guided by the Galileo

When Galileo trained his telescope to the sky, he discovered a solar system in miniature, four satellites in orbit around the planet Jupiter. Anyone with a pair of binoculars can see them. If it is clear, they are like little stars lined up either side of Jupiter.

The Galileo spacecraft's 13-year exploration of Jupiter's system was ended late last year by a fiery plunge into Jupiter's atmosphere. From Earth, like Galileo, we see the moons as points of light, but the Galileo spacecraft revealed geological features on the Jovian moons as small as the Eiffel Tower.

There are now 48 known moons of Jupiter, and Kristin Leutwyler's book illustrates them in all their variety.

Some are irregular chunks a few kilometres in size, the smallest still known only as points of light. The four largest, which Galileo saw, are rocky worlds about 3,000km in diameter. Two of them, Ganymede and Callisto, are heavily meteor cratered, not unlike our own Moon.

But two are amazingly different: Io and Europa. The nearest to the planet is Io. Jupiter's gravity massages it during its orbit and heats it up.

Volcanic eruptions occurred during Galileo 's 13-year monitoring of Io. In this book we see the volcanoes' red-hot calderas and the shifting rivers of lava through eroded channels of drifting sulphurous deposits.

By contrast, Europa is a frozen world, with ice floes shifting on a deep ocean, cracking in fractured shapes, filling recently formed meteor craters with chaotic, jumbled icebergs.

Most of the 100 full-page colour pictures in this book are beautifully clear as well as beautiful. A few are pixelated. I have seen criticism of the book from people who unrealistically demanded Hollywood production standards, evidently not realising that the best that space technology could do was to provide very interesting science. Opposite each picture is an extensive, accessible caption, mixing what must have been felt as the bitter science pill with the sweeter jam of artistic references and mythological stories behind the names of the geological features.

Leutwyler is a science journalist who skilfully spins the extended metaphors to make the science accessible. On the one hand Hollywood production values are wanted in the pictures but are not always available; on the other hand Hollywood story values are wanted for the text and are easy to provide as a matter of style. I did not need this synthetic glossiness myself, but house guests who picked up the book thought it was great. For me the science was engaging enough and I spent some hours browsing the pictures.

The book is a handy and comprehensive collection that puts the reader in direct contact with results from a marvellous space mission. If that readership is bigger because of the effort that has been made to package the science, this is a good thing.

Paul Murdin is a senior fellow, Institute of Astronomy, Cambridge University, and was formerly director of science, British National Space Centre.