#movethemoon

[scriptastronomer]

I'm writing a story about wizards who terraform planets via magic. How might a moon/moons affect their work, especially if they are moving continental plates around and creating oceans? Would there be any reason they would want to redesign the moon's orbit? If they did that, how would the planet be affected while they moved the moon?

The planetary engineers of Magrathea had to figure out that when they built the Earth. They got pretty good at it, so I guess planetary engineering isn’t that difficult to do it.

The effect of a moon on its planet depends on three things: the distance the moon orbits, the size of the moon, and the ratio of the moon’s mass to its planet’s mass.

The closer the moon orbits its planet, the more effect it will have.

The more massive the moon is, the more effect it will have.

The larger the moon’s mass is in comparison to it’s planet, the more effect it will have.

A moon will affect its planet mostly through gravity. The larger and closer the moon is, the greater its gravitational effects will be. Earth’s Moon is pretty big - both in actual terms and in comparison to Earth (the Moon masses 1.2% of the mass of the Earth). The moon orbits 385,000 km from Earth.

In comparison, Mars’ largest moon, Phobos, is only 22 km in diameter and masses less than 0.0000016% the mass of Mars. Even though Phobos orbits 9376 km from Mars, it’s so little that you can say it’s gravitational effect on Mars is zero and not be very wrong.

A moon will affect its planet by pulling on the side closest to it. On Earth, this causes ocean tides, but also flexes the crust and affects earthquakes and volcanoes. If your moon is smaller or farther away, it will raise much lower - or effectively no - tides.

I wrote about what might happen if the Moon was instantly removed from Earth then returned to it. If your people are moving continents, they’d be aware of these possible problems, and should be able to handle them with just a little bit of planning.

However, if you have the ability to move continents around, chances are you have enough power that you can handle any complications moving your moon might cause. If they get in the way, pop them into a higher orbit for a while, then return them to where they were.

Or, maybe they want to improve the planet by moving the moons because they want a brighter or dimmer night, or maybe they’ll move the moon so close that it’ll break up and form rings around the planet.

Cause rings are awesome, and will always look pretty.