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

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Discussion Overview

The discussion revolves around the feasibility of a planet the size of Earth having two moons the size of Luna, particularly in the context of stability, habitability, and the implications of such a system on human colonies. The scope includes theoretical considerations of celestial mechanics, potential life scenarios, and speculative historical narratives.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions the stability of a system with two moons, suggesting that it could be challenging to maintain without significant perturbations in their orbits.
  • Another participant notes that the presence of two moons would lead to massive tides, potentially tens of meters, complicating habitability.
  • Some participants propose that a gas giant with Earth-like moons might present a more stable scenario for such a system.
  • There is speculation about the origins of the second moon, with ideas ranging from it being a captured body to historical tweaks involving ancient civilizations like the Romans.
  • Concerns are raised about the implications of life on the moons, particularly regarding the survival of colonies from Earth and the dynamics of conflict between them.
  • One participant emphasizes that smaller moons could mitigate tidal issues, suggesting a potential design for the moons in this hypothetical scenario.

Areas of Agreement / Disagreement

Participants express a range of views on the feasibility of such a system, with some suggesting it is tricky but not impossible, while others highlight significant challenges. No consensus is reached regarding the stability and habitability of the proposed system.

Contextual Notes

Participants acknowledge various assumptions about orbital mechanics, the nature of tides, and the historical context of the moons' origins, which remain unresolved and open to interpretation.

Who May Find This Useful

Readers interested in speculative astrophysics, celestial mechanics, and the implications of hypothetical planetary systems may find this discussion relevant.

Noisy Rhysling
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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?)
 
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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.
 
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?
 
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.
 
mfb said:
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.
 
Ah, okay. The smaller the moon, the better the issue with the tides.
 
mfb said:
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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