Rachel Neumeier

Fantasy and Young Adult Fantasy Author

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Building Worlds

There’s nothing like reading 2312 by Kim Stanley Robinson to get you interested in worldbuilding. In the sense of nuts-and-bolts planetary physics, I mean, rather than in sociology. Looking all that stuff up about early Earth history for the previous post, that’s all planetary physics, too – how to thaw out a planet that’s frozen solid, what happens to the atmosphere when you suddenly touch off a couple hundred volcanoes all at once, whatever.

And it just so happens that while I was in the mood for planetary physics, I also read a book that I really have to let you all know about, in case you’re not totally bored with the subject after KSR’s 2312. I’m not sure how I heard about it, but I’m glad I had it on my TBR shelves! It’s a book called What if the Earth Had Two Moons? by Neil Comins.

The back-cover copy says “. . . . appealing to adult and young-adult readers alike . . .”, and I have to say, well, that’s true, but this book doesn’t have a for-kids vibe to me. I can definitely see bright kids loving it, but it’s for the erudite type of kid, you know? And definitely for adults as well. I did just skim over some of the explanations of Doppler shifts and so on, because I picked up all that stuff from Carl Sagan or PBS or something when I was a kid. But Comin’s explanations didn’t strike me as feeling “too basic” or anything. His explanations of everything are almost always clear and lucid, for the nonexpert of whatever age.

It was really interesting. I have no immediate plans to switch to SF from F, but if I did, I would totally use this book while designing worlds. Comins lays out ten scenarios:

a) What if the Earth had two moons? He had one of them formed by a huge collision with a Mars-sized body, which is almost certainly how Earth got its moon, and then he had the planet capture another moon later.

b) What if the Earth actually were a moon, orbiting a gas giant? Wouldn’t that be neat, btw? How’d you like to have Jupiter in your night sky, I mean up close where you could really see it? But Comins put his Earth into synchronous orbit, so it has one side that faces its planet and one side that faces away, which certainly does strange things to life on the planet. Moon. Whatever.

c) What if Earth’s moon orbited backward? And you may ask yourself, backward forward, isn’t that basically an arbitrary designation? But it turns out that if a moon orbits forward, like ours, it gets farther and farther from its planet; whereas a moon that orbited backward would spiral inward, hit Roche’s limit and break up.

d) What if the Earth’s crust were thicker? This one was more interesting than I thought it would be, because it turns out that a thick crust means that there would be few, if any, ordinary volcanoes and subduction zones and stuff like that. Instead, the heat inside the planet would escape by occasionally melting huge swaths of the planet’s crust. Very dramatic. And a bit alarming.

e) What if there were an Earth-sized planet on the other side of the sun (a counter-Earth)? It turns out it would move forward or backward until it entered a stable LaGrange point, incidentally, and then stay put at that location.

f) What if the Earth had formed somewhere else in the galaxy (that is, besides in-between the spiral arms)?

g) What if the sun were less massive?

h) What if the Earth orbited a binary star?

i) What if another galaxy collided with the Milky Way? Which it turns out is going to happen, since apparently the Andromeda galaxy is heading our way.

Anyway, all this was really interesting and fun to think about. Lots of great stuff about how stars form, how planets form, different ways to get moons, all kinds of things. I’ll definitely be picking up a copy of one of Comin’s other books, What if the Moon Didn’t Exist??

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