The Planet Factory - Elizabeth Tasker ***

The way this book opens has the feel of an author trying too hard to get her personality across, as popular science books sometimes do. Elizabeth Tasker opens by asking an astrophysicist 'What would make you throw my book out of the window?' and as a reader, I hardly take in the next page and a half wondering why anyone would ask such a question. Then, just as I regain the ability to process what I'm reading, I get 'In 1968, Michael Mayor fell down an ice crevice and almost missed discovering the first planet orbiting another sun'. And I'm thinking 'But no one made such a discovery in 1968', not realising that this statement had nothing to do with his much later work on exoplanets (planets that orbit other stars) but was just a way to try to make the character more interesting.

Thankfully, once we get past the introductory section, Elizabeth Tasker's style settles down in a big way - if anything it goes to the other extreme and becomes distinctly dry, delivering more of a collection of facts than a narrative. However, in terms of content, The Planet Factory can't be faulted. It is excellent, for example, on planetary system formation. We're used to hand waving explanations of planetary formation from a disc of dust and gas, but Tasker shows how there's not long (in planetary timescales) for this to happen, and why it's really distinctly difficult for a cloud of dust grains to do anything more than bounce off each other, rather than clump together to form a planet.

Even in the heavy fact sections there is a tendency to use odd analogies, for example: 'this uncertainty leaves us as much in the dark about the planet's type as would the sex of a foetus with its legs crossed in the womb,' but these become less frequent after a while. Tasker gives us oodles of detail, emphasising how complex the planet formation process is, as new discoveries often make old theories wrong, or at least throw oddities into the mix. As readers, we soon realise that an awful lot is being deduced from a relatively tiny amount of data, so there is a strong whiff of speculation in the air much of the time. This is emphasised when Tasker describes the way that three planets found orbiting Gliese 581 were later thought not to exist - in the case of two of them, it was enough that the star had the equivalent of a strong sunspot to produce the misleading data.

This is the first popular book I've read about the formation of both our solar system and exoplanets that gives a real, gritty, coal-face feel for the complexity of the process involved, how much we know... and how much we don't. To be honest, it's not the most engaging book - I don't think that's Tasker's fault - it's just that as a topic it's rather like geology - probably the hardest of all scientific topics to make interesting to the general reader. It's notable that in the final section, where Tasker takes on whether or not planets (and moons) are correctly placed to be able to provide the essentials for life as we know it, things get more interesting. But if you have an interest in the solar system or planetary formation on a wider scale, and are hazy on the details, it's a must-read.

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Review by Brian Clegg