Would an Earth with two moons the size of Luna work?

  • #1
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Meaning "would a planet the size of Earth with two moons the size of Luna be a stable system?"

I'm thinking of system where the moons are inhabited and the mother planet has been devastated by an asteroid impact. Naturally, they get to fighting (humans, what can you do with them?)
 

Answers and Replies

  • #2
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Over longer timescales? Somewhere between challenging and impossible. You can't move our moon much more outwards without losing it, and squeezing in a second moon in a lower orbit leads to large perturbations of both orbits.
It will also lead to massive tides - something like tens of meters.

Our moon is too small to hold an atmosphere, that makes life on it ... problematic.

A gas giant with an Earth-like and two moon-like moons would be easier.
 
  • #3
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I wanted the travel time to be reasonable at all times. Perhaps the second moon is a new capture that "just happened" to fall into a stable pattern with the original real estate?
 
  • #4
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Tricky, but not impossible. But where did it come from, and how did life survive there?

The gas giant scenario also allows travel times of a few days, similar to Earth/Moon.
 
  • #5
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Tricky, but not impossible. But where did it come from, and how did life survive there?

The gas giant scenario also allows travel times of a few days, similar to Earth/Moon.
No life native to either moon. Just two colonies from Earth That Was, struggling to survive and finding that external enemies are better than internal ones. As for the source of the 2nd moon, I'm trying that. My first thought was to tweak history a little and have the Romans describe the sudden approach of another Moon.
 
  • #6
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Ah, okay. The smaller the moon, the better the issue with the tides.
 
  • #7
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Ah, okay. The smaller the moon, the better the issue with the tides.
Noted. The Romans would have been the last to see a tidally locked Luna as the new moon, Artume, briefly flirted with collision with the elder satellite before finding a stable place to orbit Earth.

But that's all back story.
 

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