Review of What If the Earth Had Two Moons?

What it is

A book by Neil Comins about what the earth would be like if it had two moons, and nine other hypothetical scenarios about the solar system.

I'm tempted to call it science fiction. It nearly matches the original definition of the term. It is fiction about science, carefully based on existing science.

But it is not a story. There is no narrative, other than the vignettes he begins each chapter with. Instead, in each chapter he describes a hypothetical world that is as similar as possible to Earth, except for one major astronomical difference, such as:

• The title essay What If the Earth Had Two Moons?
• What if the Earth were a moon?
• What if the moon orbited backwards?
• What if the Earth's crust were thicker?
• What if the Earth had formed fifteen billion years from now?
• What if there were a Counter-Earth?
• What if the Earth had formed elsewhere in the galaxy?
• What if the Sun were less massive?
• What if the Earth had two suns?
• What if another galaxy collided with the Milky Way?

This is his second such book. The first was called What If The Earth Had No Moon. I haven't read that one.

Impressions

Comins tries hard to correctly apply current thinking in diverse fields such as astronomy, plate tectonics. To a reader who is already familiar with those topics, he spends too much time on basic explanations, but that can't be helped.

For this book, Comins has to tread a fine line between providing too much support for his conclusions and too little.

Neither goal is entirely satisfied IMO. On the one hand, despite the vignettes, it's a dry read as popular books go. On the other hand, I was occasionally left doubting his conclusions, or at least doubting that they applied with any real certainty.

I have to wonder if it would have been better to have structured the book so that it had multiple levels of support according to the reader's inclination to explore further. Basically I'm suggesting footnotes and a bibliography. He does provide appendixes but could have done more.