Questions About the Atmospheres of Various Sizes of Artificial Planets

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I have some questions about the atmospheres of various sizes of artificial planets. A lot of this could apply to natural planets from the size of of Mercury to a radius about 1.5x Earth. My questions are about a larger range of sizes, from the smallest in my question in the following paragraph, up to Neptune-sized.

What’s the smallest size of planet or planetoid that can hold an atmosphere at the same gravity as on Earth? And denser argon to replace almost all nitrogen? (I’ll use the continent of stability hypothesis as the way to create matter that dense in my story, but I’m not claiming it as an experimentally proven real-world theory.) What if they can replenish the atmosphere if there’s some loss, say 0.2% per year? Would it make much difference if it was a sunlike star, or one much quieter? My estimate is that a radius of 100 km (62 miles) would be a sufficient size, but I don’t know how much smaller would still work.

What about various sizes of planets orbiting a red dwarf star, and thus tidally locked? How would size affect the wind speeds? Would there be howling winds near the otherwise most habitable place, the day-night border? A Mercury-sized planet made of almost all iron could have a magnetic field to protect its atmosphere, and would have gravity up to half that of Earth. I’m curious about the wind speeds on all sizes of tidally locked planets from the smallest up to Neptune-sized, even though if I want them to have magnetic fields, all of these sizes won’t be possible. They should be possible on all non-rotating planets orbiting a Sun-like star at least as quiescent, giving a situation very similar to that around a red dwarf, but without the stronger stellar wind around even a very quiescent one, nor the possibility that even a usually very quiescent red dwarf could have a flare. Even one a little weaker than a lower X-class solar one would be very damaging at that very close range.

What effect would different sizes of planets have on the average wind speeds on the surface? As I said, a Neptune-sized planet is about as large as I’d want to go, and I could have my story be in a universe with a lower gravitational constant to allow it to have a low gravity. However, unless there are some fairly good advantages, having the lower gravitational constant is not something I’d want to use, because it’s the one thing that requires the story to be in an alternate universe. One made of solid beryllium would have gravity of 1.3x Earth’s, with the same gravitational constant. On the smallest size, would there be an undesirable lack of wind? Would a Neptune-sized planet, even with a 24-hour day, still have howling winds?

This is to be on a planet without mountains, as a baseline. (How much windier would Earth be if it was a water world with no land at all? Or, would Earth with continents of low-lying land up to only a few hundred feet, and no trees, only grass, be windier than a water world because of temperature differences?) Then, how much would the presence of various heights of mountains or artificial barriers affect the average wind speed? How much effect would one barrier encircling the planet, pole-to-pole-to-pole have? Two of these? Three or more? I’m talking about reducing east-west winds, but probably having little to no effect on north-south winds. If those are also too strong, I’d want to have mountains, or artificial barriers, east-to-west, as well.

What effect would various levels of stellar flux have on wind speeds? Mars is both much smaller and has a much lower stellar flux than Earth, but can still be very windy. With the maximum carbon dioxide that humans can tolerate, and humans living near the equator, how far out can you go, with how little stellar flux? With the minimum carbon dioxide that plants can tolerate, and humans living near the poles, how far in can you go, with how much stellar flux? This is the range of stellar flux I’m asking about, an extended habitable zone.

What effect would various densities of atmospheres have on wind speeds, keeping the partial pressure of oxygen constant? Let’s say, from 0.5-10 Earth atmospheres, and realizing that in denser atmospheres, winds of the same speeds are more destructive.

What effect would various strengths of gravity have on wind speeds? Realizing that the stronger the gravity, the faster the atmosphere thins out, and the opposite in weaker gravity.

I think I’ve covered most or all of the important variables that affect wind speeds. I’d be curious about any ideas anyone has about any variables I might have overlooked, and whether some of these simply don’t have enough effect to really matter.

Because my story is to have a civilization capable of designing and creating artificial planets, the advantages and disadvantages of various sizes of them will come into play. I want to have the wind speeds be as close to real life as possible, because they are the variable I’m least confident about getting even a ballpark estimate of.

I realize that even with the best information, this still is likely to be a very rough ballpark estimate. I’d be very satisfied with a range of half to double the estimate. I’d have some idea of how many mountains or barriers would be needed, and how high, depending also upon how much the would-be inhabitants would want the winds to be suppressed.
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