# Best planetary composition for flight

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1. Dec 6, 2014

### slarty

I am trying to figure out how to make a world where flight is a lot easier. How much easier could it be on a human (or near human) habitable world?

Lower gravitational force might help although too low would presumably be untenable due to loss of the atmosphere?

A higher pressure atmosphere would help but presumably this would be less likely on a smaller world?

Heaver gases such as Krypton and Xenon – but are large quantities of these elements realistic?

Are there any other possibilities?

Finally in order to make the situation more interesting I would like to ensure there are some very high mountains and very deep canyons how high / deep could these reasonably be?

2. Dec 7, 2014

### Staff: Mentor

A denser atmosphere is probably the best way to start. You can reduce gravity but keep escpae velocity (and therefore the ability to keep an atmosphere) if you make the planet larger and less dense.
Extreme height differences need a smaller surface gravity, less erosion or more plate tectonics. Probably hard to combine that with a thicker atmosphere.

Well, you have Earth and Venus as examples, and you can tune those without making it too unrealistic.

3. Dec 8, 2014

### vemvare

Actually, strapping little "wings" to your space suit, you might be able to fly on the saturn moon Titan.

146kPa, 95K, that gives us an atmospheric density of 5,18kg/m^3 and with a gravity of 1,352m/s^2 and we see that it takes 1/29th or so the wing area of the "wing load factor" of a winged creature on Earth to fly on Titan.

Looking at this and reading an estimate of 200-250kg for these creatures, roughly estimating a wingload of 13-25kg/m^2 (on Earth), I figure a 100kg man + 50kg space suit wouldn't need very big wings to fly about in the Titanian atmosphere.

Edit: Terminal velocity, if I understood the concept correctly, would be 1/29^0,5 that of Earth. So, when falling from any height, even if not in a winged suit, if you spread arms and legs out I'm quite certain the impact would be survivable.

4. Dec 8, 2014

### Danger

This might seem picky, but you didn't specify who or what would benefit from the flight. After all, it's pretty easy right here and now for birds and bugs. If you mean for humans (which I suspect to be the case), are you willing to have them physically modified such as by surgery or genetic manipulation? Reducing bone density, for instance, would make people a lot lighter, but also a lot more prone to breakage. I'm not trying to be snarky; I just want to establish the parameters.
Very much so, with one nasty caveat. The fighter jet that I mentioned in a different thread that I had designed to survive 114 g's also allowed for manned operation up to 35 g's by having the cockpit flooded with xenon and the pilot's breathing supply being oxygen with xenon instead of nitrogen as the inert element. That "device" was given to me by a friend who was peripherally attached to a US defence contractor through his job as a computer scientist. It was only after I mentioned that here on PF some 30 years later that it was pointed out that xenon is poisonous insofar as it is used as a medical general anaesthetic. Having it comprise a large part of the atmosphere would make for a pretty useless workforce.

5. Dec 14, 2014

### slarty

Thanks for all the input. A few more comments on this one:

Very useful tip - thanks. I will have a play with that idea. I suspect that an iron core would still be a good thing to help protect from the solar wind / radiation effects although perhaps a little smaller and with a lot more mantle.

That sounds very promising. Although at 95 K and 13% of Earth’s gravity I think it might be a little too 'alien' to work well. That said I suppose I could boast the pressure, temperature and gravity to compensate, although I’m not quite sure how to do even rough calculations on this. Does anyone have any thoughts on this?

By human or near human I mean sentient humanoid beings who would act in human like ways with social structures, nations, industry (and wars) etc. Think Avatar or
Edgar Rice Burroughs mars, although trying to make it as realistic as possible.

Yes I feared there would be problems with Xeon and similar. Presumably much of that toxicity could be avoided as evolution on the planet would have adapted these creatures to deal with the atmosphere, but apart form that is an atmosphere high in Xeon, say even remotely likely? I would assume that such a heavy element would be very scarce, is there a plausible mechanism where by it could become concentrated?

6. Dec 14, 2014

### Czcibor

By occasion - if you boost atmospheric pressure to insane amounts:
-you get perfect heat transfer and the same temperature, regardless whether day or night, winter of summer (except maybe in case of elliptic orbit)
-the planet should be a bit hotter than its distance to its star would imply

Xeon? I first wanted to say insane. Later: planet formed in deep space as huge ice ball, migrated, and actually... was stripped of big part of its atmosphere, and its the heavier part that remained.
Bad part: that would imply an ocean world.

Just boost oxygen / nitrogen to insane quantities, but it also mean firestorms and nitrogen narcosis for Earthlings.

7. Apr 6, 2015

8. Apr 8, 2015

### snorkack

Venus is smaller than Earth and has higher pressure atmosphere. So does Titan.
Better tune Mars. Back when the rivers of Mars actually used to flow, what was the atmospheric pressure and average temperature? And the height differences from the summit of Olympus are appreciable as well.
Mercury and Ganymede have global magnetic field but no atmosphere. Venus, Mars and Titan have atmosphere but no global magnetic field.
Try tweaking Mars´ atmosphere alone. See how you can calculate the results.
Regarding high pressure atmosphere less narcotic for unmodified man: see this
The narcotic potency of neon is estimated as 3,58 times less than that of nitrogen. Meaning that a neon atmosphere could be 3,6 times higher pressure, and 2,5 times higher density, before it is equally narcotic as same amount of nitrogen.

9. Apr 8, 2015

### Staff: Mentor

Oh well, life would adapt to higher nitrogen levels or whatever gas is present.

10. Apr 9, 2015

### snorkack

What could be plausible Ne/N ratio in atmosphere?

In Sun, the ratio by mass is: for 1 part of N, 1,8 parts of Ne, 360 parts He, 1000 parts H. Roughly correct?

11. Apr 11, 2015

### Czcibor

Depends on planet formation - Earth was stripped of all gasses crash after crash and our atmosphere formed from what evaporated from inside. No noble gas can survive that, the argon that we have used to be a radioactive potassium. In such case - trace amount of neon.

If you want plenty of neon - the planet formed in a cool place and migrated inside. Or after it formed there was some big cloud of gas in space that gave the planet plenty of volatiles. (however in such case you should have also much much more water than we have on Earth)

12. Apr 11, 2015

### snorkack

What is the neon/water ratio of gas giants?

13. Apr 23, 2015

### meBigGuy

I'd say take a world, put it in a shell, and pump up the atmospheric pressure :) Or, do a Titan/Demon/Wizard (Varley) world with high pressure. Or cheat and just say the atmospheric density is high because of a high density of attractons..

14. Apr 26, 2015

### Durakken

If we're talking about having a gas atmosphere that human can fly in and that can form in nature I think the best place to start is to ask what is the minimum mixture of oxygen. CO2, and Nitrogen that the Human body can live in and what natural elements are gases at room tempurature and pressure that are heavy/dense? enough to allow a human to act, roughly, like they are swimming?

You need to make the atmostphere something like 1000x denser to get closer to a swimming effect and Radon is only 10x.

So just doing this it's impossible and unrealistic... And the next up the Noble Gas tree we think is predicted to not follow any of the trends of the Noble Gases to continue like the near doubling of density. On the other hand there is a "realistic" way of getting around this. Make up a compound that has a high enough density that exists in a gas form at room tempurature. Kinda like a reverse water where you take to gas elements and they become a liquid with this compound you take to 2 liquid/solid elements and when you combine them you get a hyper dense gas.

This is assuming you want human flight without humans being altered. Presumably, you could use the fantasy dragon biology approach otherwise, which is have a bladder that essentially works as a lighter than air balloon.

15. Apr 28, 2015

### snorkack

No such exists. The densest gas at room temperature is tungsten hexafluoride (and incidentally it is quite aggressive).

16. Apr 28, 2015

### Staff: Mentor

Wikipedia articles suggest a mixture of neon with a bit of oxygen could be tolerable for humans at ~20 times (maybe even more) of earth's sea-level pressure, for a density of roughly 20kg/m3.

Makes airplanes really easy and really slow (unless they climb up many kilometers), but you still need a machine, just strapping on wings won't work. It also makes cars much slower.

17. Apr 30, 2015

### snorkack

Man is not well adapted to flight, yes. Various flying animals might also find flight easier.
Which neon-oxygen compositions allow infernal combustion engines to work?

18. May 1, 2015

### Staff: Mentor

I would expect that internal combustion engines are fine with most mixtures that include enough oxygen and nothing problematic* - and the limits of human-fit high-density atmospheres have more oxygen than we have here on earth.

*noble gases are as "not problematic" as it can get

19. May 1, 2015

### snorkack

An inert gas has heat capacity to take up heat released by combustion. If there is enough heat capacity, the inert gas does not get hot enough to allow combustion in the first place, and the fuel remains unburned and does not react with the oxygen diluted in inert gas.

20. May 1, 2015

### Staff: Mentor

Hmm, right. Could need different fuels, or some additional oxygen supply, depending on the gas mixture.
Luckily neon is monoatomic, which reduces its heat capacitance compared to nitrogen.

21. May 1, 2015

### HuskyNamedNala

High density, low viscosity, and if you want to get more detailed lots of upward flowing convection cells

22. May 1, 2015

### snorkack

The first post specified mountains.
How do winds circulate around Nix Olympica and the other Tharsis mountains? I´d expect the upper slopes to heat up warmer than the free air at the same altitude by day, causing winds to be sucked upslope.

23. May 1, 2015

### HuskyNamedNala

It depends. Generally there will be an up wash followed by recirculating flow near the peaks. This is why one side of a mountain may have vegetation and another absolutely nothing. Updrafts will occur where there are temperature gradients. A good example might be a large body of water in early fall, where the water retains heat during the summer and releases it slowly as the seasons change. The convection cells will only matter for low altitudes and small aircraft, though, unless you were to have a planetary storm. I think at very high altitudes the natural currents of the planet will matter much more. One of the reasons for this is because obstructions near the ground affect the velocity profile through a term known as the "reference length", denoted Zo. A good approximation for velocity as a function of altitude above the ground is V = Vo*ln(Z/Zo), where Vo is the referenced velocity at the reference length. Over the ocean, the reference length is very small (less than 10^-3 if I remember correctly), over grass or a desert it is about 10^-2 and over a city it can be as high as 10^1. You'll note that as Z (the height above the ground) becomes much larger than the reference length the approximation reduces to ~Vo*ln(Z). Keep in mind this profile is only valid for the atmospheric boundary layer and is one dimensional!

So it might be worth noting that another prerequisite for "easy" flight is constant wind speed.

24. May 2, 2015

### snorkack

It should be irrelevant to the sides of mountain: heating of the top of the mountain should create upwash up all the slopes.
Tops of local thunderstorms on Earth routinely rise above 10 km and are strong enough to matter for jetliners.
Yes, and mountains sticking into natural air currents set up lee waves, vortex streets and other such excitations.
Well, no. Soaring is based exactly on differences in wind speed.