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### What's the smallest reasonable natural planet or moon with Earth-like surface gravity?

We all know that equation for surface gravity is $$g = \frac{4\pi}{3} G \rho r$$ So if we want Earth-like surface gravity of $g = 9.81$, then the equation for radius is  r = \frac{3 g}{4\pi G ...
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### How small could an Earth-like planet be while still realistically being able to sustain human life?

I'm thinking a planet orbiting a nearby star colonized by human settlers sometime in the not near, but not too distant future. How small could a planet be while still standing in as a relatively ...
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### How do you get a thick atmosphere with less than earth-like gravity?

Basically: I want a highly viscous atmosphere but I want people to be able to walk around. I was thinking earth's gravity * 0.6 or similar. I was thinking that an atmosphere of Sulfur Hexafluoride ...
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### Habitable moon of a gas giant: working out the sizes and distances

I am attempting to create fictional, stable P-Type binary system, featuring a gas giant in a stable orbit, with a habitable Earth-like moon. “Is a Jupiter-sized planet plausible in a habitable zone?” ...
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### Making a planet habitable for humanoids: The planet

The question: What characteristics are necessary for a planet to be habitable for humans? What should the generic star and planet be like? The life forms are human, so they Need to have access to ...
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### What is the maximum orbital time for my moon around my planet?

I fear the math involved is beyond my capabilities on this one. I have what I consider to be more than a Layman's understanding of the physics involved, and I believe I can follow the math well ...
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### Habitable environment on a big moon of a gas giant lacking magnetosphere

I am trying to figure out how to make a moon (75% of Earth size) of a gas giant habitable. To give an idea of the technological level, here are technologies the colonists have access to: fully ...
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### Naturally making a gas giant moon habitable

Let's say that in my planetary system there is a gas giant around the size and distance from the Sun as Jupiter. I need the planet to be similar enough to earth to be able to be inhabited natural by ...
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### What are some plausible formation explanations of a non-hot "Fluffy" Gas Giant planet?

So, in my research and preparation for the question I asked immediately before this one, I was introduced to the concept of "fluffy" gas giants, gas giants with significantly lower density than would ...
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264 views

### What parameters are necessary to generate a plausible star in line with a spectral classification?

I'm in the opening stages of writing (yet another) star system generator, using Python. My goal is to be able to generate a plausible star and, if appropriate, planetary system around it - allowing ...
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### Could a habitable planet with lower gravity have a thick atmosphere?

I'm designing a habitable earth-like planet that has oceans, forests and life. Now this planet is a bit larger in diameter than earth but its mass and therefore its gravity is a bit lower. This lower ...
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### Can a habitable moon rely on the magnetosphere of its parent planet for radiation protection?

Science-based answers, please. Key points: the main concern is radiation protection for sustainability of human life (and accompanying plant and animal life ecosystems, whether earth-like or not). ...
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### Making a planet habitable for humanoids: The star

The question: What characteristics are necessary for a planet to be habitable for humans? What should the generic star and planet be like? The life forms are human, so they Need to have access to ...
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242 views

### Increased Luminosity in Stars

I'm trying to construct a solar system, and I'm toying with the idea that the planet capable of sustaining life was initially outside of the habitable zone, but the star's advanced age has caused the ...
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