Animals using hydrogen to fly?

Would an animal be able to produce hydrogen gas using gut bacteria and store in in sacks/bladders in it body for flight?

Hypothetically? Sure. Gaseous hydrogen can be created via biological processes, and storing it in sacs is at least possible, if somewhat improbable. What I have no idea about is how such a biological system would evolve, given the lack of any sort of selective advantage in a yummy meal floating helplessly in the air for an aerial predator to chow down on. Also...

• Hydrogen gas is highly flammable, and it is hard to see a selective advantage in members of one's species randomly exploding.
• Hydrogen gas is highly reactive, and constructing a sac to hold it in would be a remarkable feat of biological engineering.
• Hydrogen gas is extremely light and can escape nearly any plausible container, even one that's notionally airtight, given enough time.

Now, in different environmental conditions, gas flotation might be a very practical way to maintain altitude. Arthur C. Clarke proposed exactly such an evolutionary path in his novel 2001... for Jupiter. What's notable about that environment is the lack of oxygen for combustion, so these floaters don't have to worry about spontaneous detonation.

Venus is another environment in which gas flotation could work out very well, with an entire ecosystem living in the domain of near-Earth air pressure kilometers above the molten surface.

Edited by Fighteer on Apr 16th 2019 at 3:33:23 PM

I was thinking something similar to a birds airsacks except connected to the digestive system and the hydrogen isn't the primary means of lift, just something to reduce weight. The flammability would be less of an issue as the gas would be protected by skin, muscles and bone and I can't think of any reason for a creature to ignite from the inside unless they swallow fire.

I'm just not sure that biologically generated hydrogen is practical as a flotation source. I'm hardly an expert, but it seems that the challenges of producing and storing it reliably would be significant.

Edited to add: Biohydrogen is a real thing, used to generate fuel, but it is done by microbes and algae, not by complex organisms. Known metabolic pathways that produce hydrogen all exhibit oxygen toxicity — in other words, an oxygen-breathing organism cannot have a hydrogen-producing metabolism, as far as we know.

I suppose a complex organism could have symbiotic microbes that do the hydrogen production. Held in special structures, these microbes could be isolated from oxygen and provided sugars to metabolize. Then the organism would need to filter out the various waste products, including carbon dioxide, so that the H2 could be stored by itself.

It is difficult to see how a complex organism could incorporate hydrogen-producing algae, as they work by means of photosynthesis, which requires direct sunlight.

Edited by Fighteer on Apr 16th 2019 at 4:53:31 AM

Earlier I specified that the hydrogen was produced by gut bacteria, would they be exposed to oxygen?

I could see a plant doing it.

From what I can Google, anaerobic organisms can indeed live in the digestive tracts of mammals. The problem, as I said, would be isolating the H2 gas that they emit.

What about through gas exchange? Also is it just mammalian digestive tracts or are you just generalizing?

Generalizing. Gas exchange... to store hydrogen in isolation through gas exchange would require some pretty crazy mechanisms. I'm not sure how to go about it, but as I said, I'm not an expert.

Isn't oxygen and other gases moved through gas exchange?

Gases move from high density to low density. Hydrogen is the lowest-possible density gas. It is difficult to imagine a biochemical process that could isolate it.

Edited by Fighteer on Apr 18th 2019 at 11:21:59 AM

I've thought about how the hydrogen bladders could affect body shape, most large flying creatures we know of tend to have massive wingspans but comparatively small bodies, a flying creature with hydrogen in its body could develop a proportionally larger torso to better take advantage of its lighter-than-air properties.

Or use it as a bone filler, the way birds do with air.

That's actually something i've thought of, a creature with a honeycombed skeleton with hydrogen filler and hydrogen bladders in it's body, even if it didn't fly it could grow quite large.

Hydrogen is a tricky gas. To work to provide lift, it needs to remain at its natural density, but that is so low that you can't really store a lot of it in bones. Plus, it's so light that it quantum tunnels through any container it's kept in. Long-term hydrogen storage in spaceships is a real problem for that very reason. I don't know that the effect would be an issue for an organism that's capable of generating more biologically.

Peter Dickinson's The Flight Of Dragons has whale-sized dragons that fly like blimps with honeycomb-like bodies. They're too big to be prey, but the downside it that they're very fragile. They breathe fire to release excess gas. Speaking which, fire-breathing, like lighter-than-air floating, is common in fiction but doesn't exist in nature because it's impractical. Whatever its purpose is, it has no evolutionary advantage over, I dunno, less dangerous stuff. It's also difficult for animals to make fire (I'd assume the same is true of lighter-than-air gas, although it's possible). Humans do it by banging flint and rubbing sticks together.

Sorry, I just have a tendency to go off on tangents.

Edited by Lymantria on May 19th 2019 at 10:57:37 AM

"They breathe fire to release excess gas." I'm wondering what they use as an ignition source. Hydrogen and oxygen aren't hypergolic under normal atmospheric conditions. The few scientific attempts to explain dragons that I've read imagine that they produce pyrophoric gas, a liquid that is pyrophoric when aerosolized, or two different chemicals that are hypergolic when combined.

The Dragonriders of Pern series uses the pyrophoric gas version, and postulates that it's an evolutionary adaptation to the threat of Thread, an interplanetary parasite that falls at regular intervals. In the wild, dragonets chew a naturally occurring rock, swallowing it into a specialized stomach (separate from the one used for regular food) whose acids release phosphine gas, which they then store in that stomach for use. They can't store it forever, as it is toxic, so they have to chew firestone just before each Threadfall.

When humans colonize the planet, their geneticist/evolutionary biologist creates a new species from the dragonets that's large enough to ride and intelligent enough to work with its rider. And this is way off course from the original topic.

Edited by Fighteer on May 29th 2019 at 11:24:15 AM

I think part of the reason animals don't use lighter-than-air gas is becuase they simply lack the ability to produce it. And an advantage I can think off is that it makes it easier for the creature to take off and stay airborne so they serve a similar purpose to the airsacs found in modern birds and saurischian dinosaurs.

Produce, isolate, and store it. You need to:

• Use chemical reactions to produce hydrogen. This is easy; we know of quite a few organisms that do it, although none of them are aerobic. Producing hydrogen as a metabolic byproduct in an oxygen-breathing organism is improbable to the point of absurdity, but symbiotic bacteria kept in an anaerobic environment could do it.
• Separate the hydrogen gas from other gases in order to isolate it. This is quite difficult for a variety of reasons, as it involves maintaining a pressure differential, and hydrogen is highly reactive to boot. It would require a large investment of energy.
• Figure out how to store it. Hydrogen is notoriously difficult to store, since it's so light that it can quantum tunnel through anything, its pressure is low enough that it really wants to mix with other molecules, and it will react with the interior of its container.

None of this is impossible, but it's difficult to see how evolution would arrive at this particular solution given its relative inefficiency. The energy and developmental demands to use hydrogen for buoyancy in any complex, aerobic organism are just too great.

Edited by Fighteer on May 21st 2019 at 2:21:08 PM

Does the quantum tunnel thing appy to all material or is it different with organic and inorganic matter?

Any material. The hydrogen atom is the smallest of all the elements- it's just one proton bound to one electron. All other elements and chemical compounds are more complex. BTW- the term "organic" refers to a chemical compound that happens to contain carbon. Carbon is interesting because it has the ability to form chains, which can lead to some interesting complex molecules, some of which form the basis of life, but there isnt anything special about it at the atomic level.

Is there any kind of lighter-than-air gas that has a similar buoyancy to hydrogen but is easier to contain and could theoretically be produced biologically?

There's a reason that no animals in nature use lighter-than-air flotation. It's very difficult to evolve for biological systems.

Some math and concepts...

• The average density of dry air at NTP ("normal temperature and pressure" — that is, what you and I typically experience) is 1.204 kg per cubic meter, or 0.001204 g per cubic centimeter. [1]
• Looking at the densities of the lower order elements at NTP [2], you find that only the pure elements hydrogen, helium, and neon are significantly less dense than air. You might get somewhere with nitrogen, but not that far, and it would depend on the humidity and temperature.
• Hydrogen is the lightest gas by far, at 7 percent the density of air. Helium is about 14 percent, and neon about 74 percent.
• Of common gases that are compounds, only ammonia (71%), methane (54%) and carbon monoxide (95%) are lighter than air. [3]
• There is no biological way to produce helium and neon, as far as I know. However, ammonia and methane are common byproducts and/or components of biological processes, so you might get some traction there.

Methane (CH4) is just natural gas, and we know how to store it and produce it. It's a greenhouse gas, and one of the largest sources in our atmosphere is as a byproduct of the digestion of plant matter by ruminants (in other words, cow burps). So that may be your best bet. You don't get nearly as good buoyancy from it as from hydrogen, but it's the only one of the lighter-than-air gases that could reasonably be used in the way you intend.

One doesn't find children's balloons filled with methane, for the same reason we don't use hydrogen: it's flammable. It is odorless, however — the smell of natural gas is due to an additive so people can detect leaks. Unrelatedly, methane is also excellent rocket fuel.

If you want to have a bit of fun, these hypothetical methane-powered floating creatures could defend themselves by expelling and igniting some of the gas. Yes, methane dragons. You're welcome. (No, I don't know what they'd use for ignition.)

Edited by Fighteer on May 28th 2019 at 11:20:09 AM

Flint-like teeth that scrape together or a small electricity generating organ on the roof of the mouth.

Would it be possible to make some kind of new gas compound that gives the creature buoyancy and still be plausible?

I'm pretty sure we've discovered all the possible gases that are stable at normal temperature. Unless you're going to make up new laws of chemistry, I think you're stuck with what we know.

By the way, I was being slightly facetious about expelling flaming methane. One problem with that is that, to expel it from any container, the container must be under higher pressure than the air outside, substantially so if you want any sort of decent force, and that defeats the purpose of using the gas for flotation.

One could postulate separate bladders, though: some for flotation and some that are lined with muscles that can contract to force the gas out of the body to use as a weapon.

Edited by Fighteer on May 29th 2019 at 7:05:33 AM