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life on Luna?



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Sat Jun 13, 2015 7:47 pm
Stori says...



Hi, everyone. I've got a question about astronomy.

About how large does a celestial body have to be to retain an atmosphere? If our moon were that size, how would it affect the earth? I guess that's two questions.
"The one thing you can't trade for your heart's desire is your heart."
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Sun Jun 14, 2015 4:02 am
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Rosendorn says...



Size isn't the only factor to consider. You also have to consider mass of the planet, type of core, rotational speed, and how far it is from the sun (radiation can blast away any possible atmosphere because the sun is a very powerful star). This site has a whole bunch of math and nitty gritty details that helps explain the factors, but if you don't want to dig through that, I'd suggest looking up planets that have an atmosphere and finding out their characteristics. Picking similar characteristics to those planets will mean you're in the plausible range.

If you want to make the moon forcibly turned habitable, that would be another situation entirely. Look into colonizing Mars resources (such as introducing plants that would produce the gases needed to create an atmosphere) to see the possibilities.

As for how that would impact Earth, you'd probably end up in co-orbital configuration territory, where you have two large objects influencing each other. Alternatively (or maybe in tandem?) you'd have an extreme double planet configuration. Earth is already considered one, but when you impact mass by that amount then it will scale up a lot.

Off the top of my head, this is my gut instinct for how a much larger co-planet would impact Earth:

- The moon would be much brighter and I don't think it would have phases. This would impact the cultural significance of moon phases.
- It would be much farther away, because otherwise the planets could risk collision or breaking apart.
- Tide pulls would likely become more extreme, unless the planet was so far away as to not affect the oceans— in which case tides would become non-existent.
- It would potentially be a larger object in the sky, or potentially a smaller object, depending on the distance away from Earth this habitable moon was. It would probably also impact how bright the night was and how many stars would be visible outside of it.

Of course, I could be wrong. Astronomy isn't my strongest subject.
A writer is a world trapped in a person— Victor Hugo

Ink is blood. Paper is bandages. The wounded press books to their heart to know they're not alone.
  





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Tue Jun 16, 2015 4:38 pm
Stori says...



Rosey, you're a brick, as they say in England. Your name is definitely going on the dedication page.
  





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Tue Jun 16, 2015 9:01 pm
Rosendorn says...



It also dawned on me— depending on how they rotate and how their orbit influences the other's, then eclipses will also likely be far more common. Considering an eclipse is simply something blocking the sun/moon.
A writer is a world trapped in a person— Victor Hugo

Ink is blood. Paper is bandages. The wounded press books to their heart to know they're not alone.
  








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