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1

I think it would be very hard to make the atmosphere as dense as it is on Earth, because the Moon has low gravity. And you should take into account that even on Earth you can freeze to death but only on some places or in specific season. On the Moon there will be better and worse regions to live, too. The temperature on the Earth scales from around -90 to +...


6

What I'm looking for is a plausible estimate. Would one freeze to death during night time for example, or would a temperature drop to "a slight chill" be believable. Obvious answer: do you want people to freeze to death? Then fine: they freeze to death overnight. Personally, I'd rather not. The long nights are obviously problematic in this regard, ...


6

Real-world example: Operation Plumbbob Cort's answer to this question is pretty great, but makes two faulty assumptions. One, the reentry vehicles aren't the fastest objects humans have ever made, and two, they're interacting largely with the top of the atmosphere. As evidenced by the host of other answers, the theoretical side of things is difficult at ...


2

The jet from a shaped charge is one of the fastest objects on earth: formed from a flat metal liner blasted into a narrow line by a conical explosive charge, it is still essentially solid (many erroneously describe it as a liquid), but at that speed it does not behave like one. Shaped charge jets are most effective when dense metals are used (eg tungsten) ...


3

For a given value of "projectile" and an arbitrary distance... Anatoli Bugorski was hit by a particle accelerator beam in the face. The accelerator in this case was the U-70, which can impart 76GeV on a proton beam. At those energies each proton would be travelling at close to 99.99% of the speed of light. You don't need to worry about the projectile ...


8

Just as food for thought: Some fraction of c (light speed). First, you fire a laser or something that will ionize the air between yourself and the target (= create a plasma). Think big: Something that ionizes a channel that is between 100 and 1 km wide. Bigger is better. Then you use electronic and magnetic fields to move as much plasma out of the way as ...


1

Pure Oxygen at 0.2 to 0.3 atm When terraforming a planet the terraformers must make one major choice. Go for a 100% terraformed planet and pay 100% of the cost in time and resources or go 95% of the way and pay 1% of the cost. This answer assumes that the terraformers choose the second approach and that the moon will require further maintenance to remain ...


24

At what velocities would the (aerodynamically shaped) projectile just burn up? Only a few km/s. Read up on the Sprint missile, which could reach Mach 10 in 5 seconds (which would be about 3.5km/s, though that slightly depends on the altitude it had reached at that point) which resulted in skin temperatures of 3400 degrees C and needed an ablative heat ...


40

The answer depends on a mighty host of factors, including how pointy your projectile needs to be. However, we can put together a pretty reasonable upper bound by looking at reentry vehicles. They are pretty much the fastest manmade things in the atmosphere. Apollo 10 came in at roughly 11km/s. The record fastest reentry vehicle was Stardust, which came in ...


3

So the axial tilt doesn't actually influence the number of convection cells very much, afaik. It does, however, affect their position. You might also want to note that a world with a 90° axial tilt would essentially present on side to its star half the year and the other half the rest of the year. That means a long day which is summer and a long night which ...


3

Put your place between the ocean and a mountain range. Wet air coming in from the ocean tends to dump its water on the ocean side of the mountains. You get a climate like Portland or Seattle. Put your place far enough north that it gets cold. Then the wet air dumping water will come down as snow. Possibly a lot of snow. The ocean will prevent it from ...


3

Ursula K. LeGuin does a good job with this kind of environment in "The Left Hand of Darkness". Direct sunlight isn't needed, so long as there is enough radiant energy to grow some kind of crops, or to support a sufficient amount of wildlife for a hunter/gatherer society to live off of. A sunny region can produce 600 calories per square centimeter of arable ...


-1

Since the gravity is 1/6-th of that on the earth, running would probably more comfortable using longer jumps. Walking on water would not be possible - since the water experiences the same gravity, the buoyant force would be equally 1/6-th of that on earth (I neglect the surface tension here). Cats could jump from heights 6x higher than on earth. If diving is ...


6

Sulfur hexafluoride This is a real oddball and probably a sign that the planet is a terraformed low gravity planet, because this is when sulfur hexaflourite is actually useful. No natural planet would have this in its atmosphere. However looking at its description from Wikipedia: Sulfur hexafluoride (SF6) is an inorganic, colorless, odorless, non-...


6

Methane. http://aetinc.biz/newsletters/2010-insights/october-2010 Methane gas is relatively non-toxic; it does not have an OSHA PEL Standard. Its health affects are associated with being a simple asphyxiant displacing oxygen in the lungs. Miners previously placed canaries in deep mines to check methane gas levels. Reportedly, canaries keeled over ...


30

Argon might be a good replacement for Nitrogen. It's the 3rd most common element in Earth's atmosphere, although only at a 1 % ratio. Argon is also heavy enough to sidestep the issue of losing most of it to space like some of the other noble gasses. It is however a little heavier than oxygen, which could pose the danger of it settling in lowlands. Argon is ...


3

There are other inert gasses with reasonable cosmic abundance... neon and argon spring to mind. Neither are particularly common on earth (argon makes up 1% of the atmosphere, and neon is much rarer than that) but given that you're handwaving away the nitrogen in the air then handwaving in noble gas replacements isn't entirely farfetched. Both are safely ...


13

what's my atmosphere made of? Nothing else in significant amounts. As you state, oxygen has the same partial pressure of Earth. Thus around 0.2 bar. Let it be that, plus traces of other oxides, like water and carbon dioxide. In this way you don't have to worry about adverse effects, and you just need to take care of higher pressures because of oxygen ...


14

Helium. It is so safe to us, it is used in an array of different kinds of surgery to inflate your abdomen so it is easier for doctors to get to hard-to-reach organs. This article is from 1995 - a lot has changed since then, helium is much more commonly used today because of its non-toxicity. Helium may be rare on Earth, but scientists think it may make up ...


1

You can have the people genetically engineered to have vacuum-resistant lungs and maybe cardiovascular system, so they can use a face mask and not get an embolism. Another possibility is Kurzweil's artificial red blood cells, which could keep them oxygenated for minutes to hours without breathing.


6

Short answer: yes. Long answer: a breathable atmosphere is defined as an atmosphere were we can breathe, thus containing the gases we need to carry out this physiological process. This basically requires oxygen with a partial pressure of about 0.2 bar and no gases with a lethal effect on us. Since the buffer gases you are using are those commonly found in ...


0

If you want to have a substantial pressure gradient, and you want it stable over geological eras, you need something to oppose the gradient. What can you use? But of course the planet rotation, which when fast enough will tend to spread liquids, gases and even solids along the equator. Since you want it to be stable over billion of years, you cannot ...


4

Short answer, no, this is not possible. The column depth of an atmosphere is based on the gravity of the planet and the total mass of the atmosphere. A gas will expand to fill its container (that's the prime definition of a gas), and in this case the container is the extent that gravity can hold it to the planet. However, all is not lost if you're willing ...


7

If you wish for more UV light to reach the poles, you can deplete the ozone layer over them. This is exactly what happened on our world - ozone depleting chemicals reached the upper layer of the atmosphere and due to wind currents they concentrated over pole over the decades, specially the south pole. The hole over the south pole is shown as the blue-ish ...


0

The oxygen in your atmosphere will convert the ammonia to nitrogen and water. 4NH3(g) +3O2 (g) → 2N2(g) +6H2O(g) source This is like the fate of methane in our atmosphere of oxygen excess. Oxygen strips away the hydrogens to be its little pets and then double teams the carbon. I think with NH4 there may be nitrogen oxide intermediates for a while but ...


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