What if the Earth had two Moons? – Neil F. Comins ***

There is a great idea behind this book. Why not, as a thought experiment, change the parameters of our solar system and see how things would be different, using this to explore cosmology on a wider scale. So, for instance, the book goes through the title scenario, but also what if:

• the Earth were a moon?
• The Moon orbited backwards?
• The Earth’s crust was thicker?

… and so on for a total of 10 scenarios. Along the way we’ll find out more about everything from black holes to the Big Bang, but particularly lots about how planets and solar systems form and function.

In principle this is wonderful, but the execution has three problems.

Firstly there’s the way that the ‘What if’ concept is approached. Although the title specifically says ‘What if the Earth had two Moons?’ the chapter actually describes a planet called Dimaan that’s a bit like the Earth and has two moons. This is frustrating, as I really want to know what the actual Earth would be like, not a planet like Earth. This approach means Neil Comins is always flipping between describing the Earth and Dimaan (etc.), which irritates. I also find the science fictional naming a bit painful – so, for example, the second chapter has a system where the Sun is called the Zon. Why?

Speaking of fiction, the second problem is that each chapter begins with a rather painful bit of fiction set on the world that chapter is dealing with. The people who feature in the stories are human, and sometimes even are real people like Galileo or Columbus. This is both confusing and twee. Some of the storylines are bizarre. In one two children are presenting alternative theories at the Royal Society. Why would children be presenting at the Royal Society? And worse still, there’s an elementary plotting error: the second child doesn’t even get a chance to present her theory because she gets an asthma attack. Why? It doesn’t go anywhere. This is just self-indulgence.

Finally, I have to confess that by about the third chapter it all gets a bit samey. Ok, each of the scenarios have interesting implications and we keep getting extra snippets about the universe as a whole, but in the end we keep reading about how various parameters of the Earth (or rather, the not Earth) would be different, and what started as a fascinating concept ends up as a rather nerdy detailing of information that isn’t of great interest unless you specialize in planetary behaviour. The best science writing can take the mundane and make it exciting. This takes the dramatic and makes it mundane.

There’s no doubt that there is a lot of good stuff in here. Comins knows his astronomical onions and packs in lots of information in his 10 interesting scenarios. It’s a great idea. But even the best ideas don’t always work as you hope – and that’s what I found with What if the Earth had two Moons.

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Review by Brian Clegg