Jan 11, 2010

Moon(s)

What better way to signify that a someone is not on earth than to have them look up and see a different moon, or even more than one?

There are a couple ways the moon(s) will effect you planet besides making the night sky prettier.




1) A moon's gravity tugs at your planet and is the main cause of tides. Additional moons would make the tides more complicated since sometimes the moons would work against each other, and sometimes they would add their power together. The strength of the tide is also strongly varies by the shape of your oceans. Generally bigger bodies of water have bigger tides, since there is more room to slosh around, which is why tides are negligable in lakes. The way that the ocean floor and coastline funnel the water also has a big effect on the strength of the tide.

The Celestial Architect Spreadsheet will calculate the magnitude of your planet’s tide, taking into account one moon at a time. You'll still have to figure out how the tide varies from place to place by yourself.  I guess i’m a land-lubber since i’ve resolved to mostly ignore the tidal question by designing a moon that causes far more modest tides than Earth has.


2) Stone is more resistant to tugging than water, but it is not immune. If the moon is close and massive enough it will significantly flex your planet’s crust. In other words shift your continental plates more and thus cause more earthquakes and volcanic eruptions. I don’t have any formulas for this. It is an open question weather our Moon is massive enough to provide a significant earthquake effect. If your Moon has a tidal magnitude many times greater, you may want to consider writing in frequent earthquakes into the world.


3) A moon can’t be too close. A moon that passes Roche’s Limit will tend to be ripped apart by the difference between the gravity on it’s near and far sides.

4) A moon also can’t orbit too far from it’s planet otherwise it will get snagged by your star and wander away from the planet.


You can use the "Size & Moon" page of the Celestial Architect Spreadsheet to calculate all these things for you.

For more information, including the formulas see the excellent section on Moons from Creating an Earthlike Planet.



Aside from the decision to have less tides, i’m going to put off designing the moons for Orb. Though i’m really impressed by the appearance of Io, (at the top of this post) and will try to include one of these pizza moons, if i can make it work.  I'm not sure at the moment what conditions are required to keep a small moon volcanically active.

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