## Friday 31 July 2020

### Ballonts VI; back from the brink, or still lead balloons?

Over the years, many readers expressed how sorry they were to learn that ballonts, i.e. lighter-than air lifeforms, were almost impossible to achieve on an Earth-like planet. The only way you can have a ballont on such a world is to shape it similarly to actual balloons on Earth: they have to be very, very large. What I had badly wanted was ballonts as aerial plankton floating through forests, or small ballont 'seedlings' released by their parent organisms, or something tiptoeing over the plains, as in the previous post. Such ballonts were an integral part of the Furahan menagerie, until I sat down to do the math. The sobering results are to be found here, here and here.

With that knowledge in mind, I was quite surprised to see a video showing a very small balloon on YouTube. I copied two stills from it to show you, but advise you to see it on youTube.

The video shows a very small balloon, of a size that would lend itself very well to a ballont! Was I wrong to think that small ballonts, or small balloons for that matter, are impossible? The video's narrator says that the balloon weighs 0.3 grams and needs only "naught point five eight litres of helium to float". The video shows a hand releasing a string, or so we assume, as I do not see the string in question, and the image of the balloon then rises. That sounds like a strong assertion that the balloon actually goes up into the air when released. But the video was made for advertising purposes, and advertising and truth are not the best of friends. Beware: the part where the balloon rises after being released looks like an animation rather than live action, and in the rest of the clip there is no actual video of the balloon floating.

Luckily, they showed numbers: the video specifies a volume of helium, of 0.058 L. Volumes do not depend on weight or mass, so I suppose they meant the volume of the inside of the inflated balloon, as that seems the only thing that would make sense. We can easily find out how large a sphere should be to take up 0.058 L. Turn that into cubic meters, apply the equation for the volume of a sphere (4/3 x pi x R^3 with R as the radius of the balloon), and you get a radius of 0.024 m, or a diameter of 4.8 cm for the balloon. That looks like the size they showed in the clip. Very well, but how much mass can that volume of helium actually lift?

Well, under 'standard' circumstances, meaning 20 degrees centigrade and one atmosphere, the density of helium is 0.179 kg per cubic meter, and of air 1.2019. From that it is easy to calculate the mass of 0.058 L of helium and of 0.058 L of air. Subtract the two, and that is the mass you can lift. You get 0.059 gram. That is almost nothing! Mind you, for a balloon to work it must first lift the mass of its own envelope. In this case, the envelope has to have a mass LESS than 0.059 gram, or else it cannot float. Good luck with that. I am beginning to think that the balloons in the clip were not kept aloft by a bit of string, but that they were held up by a length of stiff wire.

Still, I wondered if there was anything to be done about the physics. In my previous models, I had used the characteristics of PET for the membrane of the balloon, because that is a strong material that will not let even gases escape. Unfortunately, PET has a density of some 900 kg per cubic meter, so it is only a bit less dense than water.
 Click to enlarge; copyright Gert van Dijk

Here is my old model again. The x-axis shows the radius of spherical balloon in cm and the y-axis shows mass in grams. A balloons works if there is a mass difference between the displaced air and the gas inside the balloon. If that difference is larger than the mass of the membrane, you get lift. In the graph, the red line shows lift: if the values are negative, the balloon sinks, and if they are positive, it floats. This PET-balloon will not float if the radius is smaller than 25 cm; that is a big balloon. Actually, that is MUCH bigger than the balloons you can buy for parties. The membrane of latex balloons must weigh a lot less than the one in my model.

 Click to enlarge; copyright Gert van Dijk

Here is the same model, but now the membrane is magically completely massless. That helps a lot! Mind you, that third power is still being difficult: a balloon with a radius of 10 cm can still only lift 5 g. To lift just one gram, you need a radius of 6 cm. Even without such a weightless membrane you cannot have truly small balloons. This raises the question what the mass of a typical children's balloon is, and how small manufacturers can make them?

I asked balloon manufacturers, and they were friendly enough to reply. It turns out that helium balloons of 9 inches can float, and that 5 inch balloons are the smallest ones to float. But they do so weakly and only for a short while, because the helium leaks out though the latex. Now, I refuse to use illogical mediaeval units of measurement, so I will substitute 12.5 cm for the width of five working men's thumbs held next to another. That is a radius of 6.25 cm.  The manufacturer told me that the weight of such a balloon is roughly 0.7 g, if made out of white latex. The colour affects the weight.

Well, that makes sense if you compare it to the magical massless membrane: the magical one could lift one gram with a 6 cm radius, and now we find that the actual weight of the membrane of a balloon of that size is 0.7 g. That leaves 0.3 g for lift. That is just enough.

Today's lesson is that physics still conspires against ballonts. A secondary lesson may be that advertisers can waste your time. I knew that already. Sigh.

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PS this is an additional figure I had prepared but not posted. However, it ties in so well with Abby's comment below that I decided to add it.

 Click to enlarge; copyright Gert van Dijk

chunderbird said...

how about a ballont that uses aerial jet propulsion to fly? like somehow it can store compressed air in special bladders and expel the air to rocket its way along while flipper like rudders aid in propulsion and lift but the main source of lift is still a gaseous sac?

tribbetherium said...

The question would be: what kind of niche would a ballont concievably fill? Not to mention how the easily-rupturable flotation sac would make them vulnerable if they had no backup means of propulsion. Regardless of the physics the question of whether a ballont would even survive in an evolving ecosystem is questionable, especially if wing-fliers and jet-fliers would easily outcompete it in whatever niche it tries to occupy...

Anonymous said...

chunderbird: rocketing can work 9there are even squid that can jet out of water for short periods), but the problem is that the supply of air is likely to run out very quickly, and then the animals sinks.

tribbetherium; when the ballont idea first came up their ecological likelihood was never considered; they just looked nice...
And now we know that small ballonts are impossible, so the question is moot. But I will give it a go. Their advantage might well be that they probably have very low energy requirements and can yet go anywhere. We have no parallel of their Bauplan on Earth , so it is not that easy to think about factors determining their success or failure. Amphibians and lizards might on paper seem to be inferior to mammals, and overall they may well be. And yet both groups thrive, albeit in specific circumstances.

Abbydon said...

I have followed your articles about ballonts with interest and it is clear that it is the membrane mass that causes the problems. While a large ballont does address this problem at some point internal structure within the balloon would be required, so I suspect simply getting bigger introduces additional problems.

Therefore, is making the membrane thinner a better approach? For example, if you bubble hydrogen through soap solution you can make small bubbles than float. A quick calculation with a 1 cm radius bubble with a 1 micron thick membrane made of something with a density approximately the same as water gives the following:

Displaced air mass: 5.1 mg
Hydrogen mass: 0.4 mg
Membrane mass: 1.3 mg

This suggests that 3.4 mg of additional mass could potentially be carried. If you replace the lifting gas with methane to reduce diffusion loss then 1.1 mg is still possible.

While this perhaps doesn't sound impressive obviously microscopic life could hitch a ride on bubbles like this. Maybe algal colonies could produce a sort of mobile plant, though there are obviously a few other issues that would need to be addressed before this seemed plausible.

However, perhaps more interestingly individual worker ants apparently weigh between 1 and 5 mg, so it's even in the right ball park for a small insect.

Even better, fairy flies are smaller than ants as they are less than a millimetre long. I'm not sure what their weight is but I've seen estimates as low as 25 ng.

Of course, it would always be possible for multiple bubbles to stick together to make a sort of foamy lifting mass which could carry a greater weight. This would even provide a sort of internal structure that would make the balloon somewhat more robust than a membrane only balloon.

Throwing some vague numbers around it seems possible that the tiny 7.7 mm long frog paedophryne amauensis could be lifted by a spherical methane bubble foam with a radius of 6 cm.

I have no idea how such organisms could evolve and remain competitive, but it does seem that having a much thinner membrane with a soap bubble rather than a polymer is perhaps a viable approach. Diffusion of the lifting gas out of the bubbles would of course be one of the problems that might "puncture" the idea though...

Sigmund Nastrazzurro said...

Abby: thank you! I had come to the same conclusion about the importance of the membrane. I had in fact made another figure to show what happens if you give the membrane a density of just one fifth of that of PET, but had left it out. I have now added that figure to the post, also drawing attention to your comment. Your comment and that figure fit well together.
What happens is that the 'minimal lifting radius', i.e. the smallest radius at which the balloon floats, moves to the left the less mass the membrane has. For the 'magical massless membrane' that point lies at zero mass, and it lies somwhere to the right of that for real-life membranes.
I did not check your calculations, but believe them, as the principle is sound. Physics does allow balloons of microscopic and larger sizes, but the problem is getting a suitable membrane: extraordinarily light, impervious to gas exchange, and strong enough to last a while. That is the real challenge for ballonts.

ypsigon said...

if small ballonts don't work what if they have a multi stage life cycle becoming ballonts only when big but are wing flyers as larvae

Abbydon said...

Just because I get distracted from work easily, I have been doing more research on this and came across an interesting Nature article published a few months ago.

Limits on gas impermeability of graphene

Despite being only one-atom thick, defect-free graphene is considered to be completely impermeable to all gases and liquids. This conclusion is based on theory and supported by experiments that could not detect gas permeation through micrometre-size membranes within a detection limit of 10^5 to 10^6 atoms per second. Here, using small monocrystalline containers tightly sealed with graphene, we show that defect-free graphene is impermeable with an accuracy of eight to nine orders of magnitude higher than in the previous experiments. We could discern permeation of just a few helium atoms per hour, and this detection limit is also valid for all other tested gases (neon, nitrogen, oxygen, argon, krypton and xenon), except for hydrogen. Hydrogen shows noticeable permeation, even though its molecule is larger than helium and should experience a higher energy barrier. The puzzling observation is attributed to a two-stage process that involves dissociation of molecular hydrogen at catalytically active graphene ripples, followed by adsorbed atoms flipping to the other side of the graphene sheet with a relatively low activation energy of about 1.0 electronvolt, a value close to that previously reported for proton transport. Our work provides a key reference for the impermeability of two-dimensional materials and is important from a fundamental perspective and for their potential applications.

It seems that a single layer of graphene can be used as the magic massless membrane as long as the gas inside isn't hydrogen. I'm not sure how large a balloon you could make with graphene but since its surface density is very low at around 0.8 mg/m2 you could just use a lot of millimetre sized mini-balloons instead. This is not quite as a good as a single balloon but the mini-balloon cluster would still provide lift and also be more robust than a single balloon. This also allows the organism to grow incrementally by adding additional mini-balloons as required.

This paper therefore suggests several possibilities:

1. Use single layered mini-balloons containing methane
2. Use single layered mini-balloons containing deuterium
3. Use double layered mini-balloons containing hydrogen

Assuming life can produce defect free graphene sheets of a suitable size then this may be the most viable route to a ballont on a planet similar to Earth.

Keenir said...

I rather like Abby's ideas of using bubbles, be they solitary or in groups...we know frogs can produce foam to encase their eggs in (ballonts as egg cases that can navigate a little once the tadpole hatches?)...ditto for some insects.

Tribbetherium -
> especially if wing-fliers and jet-fliers would easily outcompete it in whatever niche it tries to occupy...
Ah, but until either sort of active flight evolves, any ballonts would have the skies to themselves. (look how long separates insect flight & backboned flight...and it could've been longer had archosaurs perished at the end-Permian)

Keenir said...

that was I, anthony docimo.

Keavan said...

I've always thought heavier than air ballont-like animals, which regulate height using powered flight are interesting, plausible, and underrepresented. Why not have inflated, flapping deltawings, or creatures that bound along the ground in lazy arcs?

Sigmund Nastrazzurro said...

ypsigon: that is a good idea, suggested before. Commenters in the past came up with the idea that young ballonts could grow while attached to their parent. That would work, but how do you get the system going? somehow you need land- or water-based organisms that grow large balloons, that then split off as separate organisms. But for that to work, there must be an advantege in growing a large balloon in the first place...

Abby: fascinating! You may have found the only (?) solution for ballonts on Earth-sized worlds. I have no idea whether graphene layers can be produced by living organisms. The ability to do so would probably have to evolve hand-in-hand with a purpose for such layers. Initially, that would probably not be to obtain lift, because the amount of lift is still ridiculously tiny. But it is very tempting...

Unknown/Anthony: I had played with bubbles before and have some old sketches somewhere of mats of bacteria or algae or some such covering pond surfaces. By producing stable bubbles they would slowly add bubbles until the mat is lifted in the middle, and the parts hanging down would keep all the bubbles in an envelope. I thought it would be a nice dispersal mechanisms. For that, it would only have to keep adrift for a day or so. I liked them because they would be great visually. But can a bubble keep from popping that long?

Keavan: Powered ballonts would be great. I really liked those, and sketched some in the past. Please have a look here: https://planetfuraha.blogspot.com/2008/09/ballonts-ii.html
Their problem lies in where you wish to situate them: on an earth-sized planet with an Earth-like atmosphere, the balloon part would be so large that no amount of lapping could overcome wind resistance, or so I figured at the time. Unfortunately, that still seems very likely.

Abbydon said...

Soap bubbles break when the bubble film becomes too thin. This primarily happens because of evaporation though gravity pulling water to the bottom of the bubble also has an effect. Therefore, bubbles are longer lived if the air temperature is lower, humidity is higher, or if the bubble mixture contains chemicals (e.g. glycerine) to reduce evaporation. I suppose if life is involved there could also be some way of replacing lost water or simply recycling the liquid to make more bubbles as old ones pop.

I believe that the British scientist James Dewar investigated bubbles about a hundred years ago and I have seen quotes that he managed to get a 19 cm diameter bubble to last for over three years and a 32 cm diameter bubble to last for 108 days. No doubt his experiments were under unusual conditions but it does suggest long life times are possible under certain circumstances.

Keenir said...

I, Anthony is typing this:
I would think that it has to be possible to have the bubbles last a day or more, given what insects and frogs can accomplish; the question is if it would have to be constantly expanding (always making more foam/bubbles) or if it could be periodic, maybe adding to the size only once a day.

food for thought: https://www.thoughtco.com/bubble-life-and-temperature-project-609020 & https://en.wikipedia.org/wiki/Soap_bubble#:~:text=The%20longevity%20of%20a%20soap%20bubble%20is%20limited,soap%20film%3A%20water%20falls%20down%20due%20to%20gravity. & https://en.wikipedia.org/wiki/Sea_foam#Longevity_and_stability & eggs in foam: https://en.wikipedia.org/wiki/Egg#Fish_and_amphibian_eggs

slightly blocked, but intriging title: https://www.education.com/science-fair/article/lifespan-bubble-extended-temperatures/

Keavan said...

I suspect that would only hold true for organisms gaining the vast majority of their lift from a lifting sac. The larger and more effective the wings are, the smaller the balloon you could get away with is.

Just like there's a spectrum from neutrally buoyant flyer to swimmer, there is one from neutrally buoyant flyer to heavier than air flyer. Creatures with hollow bones like birds are already taking the first step, and pterosaurs, which (if I'm remembering correctly) had air sacs in the wing to create an airfoil shape, are taking that a step further. If an organism started filling its bones and air sacs with hydrogen or methane, you'd have the makings of a protoballont. Obviously this hypothetical creation is still a lot closer to heavier than air than an actual ballont, but by changing the body shape to increase the size of the lifting sacs, you could get a reasonable and alien-looking half-ballont.

Sigmund Nastrazzurro said...

Abby and Anthony: intriguing. Instead of a big sac, we are looking at a cluster of gas-filled microbubbles. If the cluster is spherical, the part that is exposed to the air will be minimised. Over time, a bubble will burst, but it may be some time before the ensemble loses lift. I can see that working for a non-flying parent producing clusters with embedded seeds or embryos, because that would minimise the lift needed. I am tempted to use that for a painting.
But would it work for an entire organism including digestive, reproductive and bubble-producing organs, etc. ?

Anthony: I'll look at the links later (no time now)

Keavan: I like the idea of a spectrum, and indeed that was the driving force behind the ballont drawing in the earlier post. But the animals in the spectrum in that post do not come from one world, but from world with increasingly dense atmospheres. The problem seems to be that little balloons make hardly any difference.I cannot do the math right now, but my reasoning follows.
Take a bird, say a 1 kg herring gull. Reduce its wing area by one half which reduces the lift the wings provide by one half. The other part of the lift will have to be provided by a balloon. That amount of lift would have to cater for about half the mass of the bird (actually probably a bit less because the smaller wings would need smaller muscles). How large does the balloon part have to be to lift 0.5 kg of gull? Well, that brings us right back to membrane mass; if you take latex or PET, you can look that up in the earlier graphs. I fear that the balloon would be so large that the animal as a whole would be in trouble: it would be vulnerable to wind, and would not be able to fly fast, which would reduce lift produced by the wings. This really needs a more thorough analysis, but nature conspires against small balloons. .

Keavan said...

Ah, shoot, I see the issue. Heavier than air fliers are only really feasible when small/medium and aerodynamic, while ballonts are only somewhat viable when large and round. Wings large enough to propel a large ballont wouldn't be able to create enough lift to counteract their added weight, and a balloon large enough to lift some of it's own weight and some of that of a medium flier would create a great deal of drag.

Sigmund Nastrazzurro said...

Keavan: yes, that's what I thought too. Ballonts might work on planets with incredibly thick atmospheres, but then are nearly swim bladders. Worlds with atmospheric pressure over 100 times the earth one complicate matters too much for my taste.

Keenir said...

I, Anthony Docimo, do say -
this is a very fun conversation

>But would it work for an entire organism including digestive, reproductive and bubble-producing organs, etc. ?
It ought to work for an entire organism...given the restrictions of flight. (ie, when birds get toooo heavy, their flying ability plummets - like in hoatzins)

So, minimize the internal organs that can be minimized, lose the ones that can be lost, change behaviors where possible (like how vampire bats will feed & then almost immediately pee so they lose all the weight they just drank)

Worst comes to worst, just declare ballonts a form of technology - a gift from gas giant natives, modified to survive on rocky worlds. (as such, their anatomy may be classified and not permitted to be disclosed)........or rocky world-native spacefarers many millions of years ago wanted ballonts to exist, and they took parts of various local genera and assembled ballonts.
:D

Abbydon said...

Just for completeness, I thought I'd go into a bit more depth on the soap bubble idea and leave the graphene approach for later.

Firstly, I'm going to assume that the bubble producing organism can add proteins and stuff to water to make "bubble mix" and that this mixture will still have approximately the same density as water. This is reasonable as the hagfish is renowned for producing copious amounts of slime to deter predators but apparently one litre of slime only contains 40 mg of proteins and mucus, yet is still the same density as water.

As in my earlier calculations, a 1 cm radius bubble with a 1 micron thick membrane containing hydrogen can carry up to an additional 3.4 mg of mass. This is perfectly fine for small insect type creatures which include full digestive systems and so on. The bubble producing organs might require a bit more thought to determine if the volume of gas required is too large for a small organism to generate especially if the bubble is not permanent. Interestingly, it appears to be possible to generate hydrogen using algae so perhaps a solar powered symbiotic bubble is possible.

However, if we are interested in a larger organism then multiple bubbles in a cluster are needed. I'm not quite sure what this implies for the bubble thickness, but simplistically we could assume that each individual bubble only has a half micron thick membrane though when combined this would be back to the original 1 micron thick membrane. This implies that each individual bubble can then contribute 4.1 mg of lift.

As there are several small frogs, geckos and chameleons that are less than 2 cm long and have a mass less than 200 mg this seems a plausible minimum size for a viable vertebrate type organism. This suggests that at least 50 individual bubbles are required in a cluster to provide sufficient lift. This would produce a spherical cluster with a radius of about 3.6 cm (assuming the same total volume as a single spherical bubble).

The end result of this is that we could have a 7.2 cm diameter bubble with a 2 cm long organism hanging underneath. It would need long hairs/fingers/wings/etc to retain contact with as many of the bubbles as possible, so it would sort of be an upside down pond skater. I'm not quite sure how it would feed but the idea of a mini chameleon floating around catching insects with its tongue seems amusing. It would perhaps need some fins or wings to be able to steer slightly, but this seems possible. It's unclear how it could influence its vertical motion but perhaps dynamically increasing or decreasing the amount of hydrogen in the bubbles could work.

Or perhaps they have no control over bubble motion and instead it acts like a mobile sticky spider's web to capture prey which are devoured when it lands? This is a bit like a "ballooning" spider and apparently spiders over 100 mg have been observed "ballooning" using a metre long sheet of silk! A central bubble mass surrounding by long strands to act as a sail could be a hybrid approach to gain altitude. The sail could even be pulled in to descend more gracefully than spiders can do.

I suspect that there are a few more questions to be asked about the viability of such an organism but it does seem to be almost plausible at this stage.

Sigmund Nastrazzurro said...

Abby: very interesting. I started to think about a painting of a 'cluster ballont'. If so, it seems right and fun to name it after you. If you are interested, let me know and we can discuss it through email (nastrazzurro AT gmail. com (I do not visit that email address regularly).

Keenir said...

I, Anthony Docimo, say:

I like that proposed ecology, composition, and nature, Abby...my only quibble is to ask why it needs to land before it can feed? Some species might require land, I con't contest that; but I wonder if more would use the time "in flight" (in float) as the time to catch their prey. (and some of *those* might prefer to store the caught food for themselves or their young when landfall is made)

Abbydon said...

I mentioned landing as it seems more plausible that the soap bubbles are temporary as compared to a permanent rigid membrane. While you can increase the longevity of soap bubbles under ideal conditions by preventing evaporation this doesn't stop the hydrogen diffusing out. I can't find any rigorous papers that I can access but surprisingly I think that hydrogen doesn't escape much faster than air through the bubble membrane as it is not very soluable in water.

It may be possible to top up the hydrogen dynamically but I haven't considered if the rate of hydrogen generation is comparable to the diffusion loss. I don't know if anyone would complain if that was assumed without hard numbers though.

Of course, bubbles will eventually pop from evaporation losses thinning the membrane or from impacts. Creating new bubbles "in flight" may be viable as it doesn't take much water so feeding may be sufficient to provide the raw material. However, at some point it seems that landing and regenerating the bubble cluster would be the best option.

Devouring the remaining bubbles to recover the mucus and water at this point seems like a good idea, just as spiders do with their own webs. Anything organic stuck to the mucus is also a convenient meal but it would also reduce the overall lift so it naturally will descend when the "web" is full. I suppose it could be possible to feed in flight but that seems challenging to do if it is eating what is stuck to the bubbles. It could work if there were separate sticky threads trailing below the bubbles like the ballooning spiders example though.

This could result in an organism that produces the bubbles before dusk and lifts off during the night when the temperature is cooler (i.e. reduced evaporation losses) and the air is calmer. Perhaps bioluminescence could be included to attract small insects to the sticky mass just like some fungus gnat larvae do. I imagine that artistically this would look good too. At some point the bubble descends and the organism has until dusk the next day to devour everything stuck to the bubbles and excrete what it doesn't need to reduce weight.

I had only intended to give a short reply but once again I seem to have produced a short essay. I hope no one minds that. At least now in my head I have a vague idea how something could evolve in steps from something like a froghopper into an airborne nocturnal jellyfish though.

Keavan said...

On the topic of ballooning spiders, its interesting, and perhaps useful, to note that their lift is generated more by the negative charge of their silk being repelled by the ground and attracted to the atmosphere

https://www.theatlantic.com/science/archive/2018/07/the-electric-flight-of-spiders/564437/

A Human said...

I remember someone suggesting "vacuum balloon" ballonts in a comment on a previous post, (If you make a structure with nothing buta vacuum inside it is lighter than a structure containing air or other gases, but it needs methods of support other than gas pressure since there's nothing inside it) and there was a reply that said that vacuum balloons were too hard to maintain to be likely in biology.

If there was a ballont that had a way of maintaining its shape other than gas pressure, (maybe a net/skeleton of rings made from rods that constantly try to straighten) could that allow it to use much lower-pressured gas to float, making it lighter even if the support structure wouldn't be able to retain integrity if the inside of the ballont was a vacuum?

What I'm basically saying is you've shed doubt on ballonts relying on gas pressure balloons, but perhaps there is a way of providing more lift/structural integrity if the gas pressure inside is less than the gas pressure outside (instead of being allowed to equalize) while still not going full vaccum-balloon.

Keavan said...

@A Human

Vaccum chambers are generally pretty heavy because they need to be strong. Maybe something like graphene as suggested above would work as a membrane.

Even then though, most vacuum chambers are pretty small because as they get larger, the chances of a defect that causes an implosion or leak gets much higher.

Also I don't think vaccums create significantly more lift than hydrogen, but are significantly harder to produce.

Abbydon said...

@Keavan: I was unaware of that and it's certainly very interesting. I shall be thinking about that a bit more at some point when I have time.

Anyway, here are some more of my thoughts on a graphene based solution.

As previously mentioned, a (theoretical) foam of small double-layered graphene bubbles seems viable as it is extremely light yet impermeable to gas. Conveniently, something similar to this called Aerographene has already been created. It has a density slightly lower than helium at 0.16 kg/m3 though this doesn't mean it would float on it's own.

If you assume life could create something vaguely similar containing many sealed bubbles of hydrogen then it would be ideal. Most importantly, the lift would scale linearly with volume at 0.98 kg/m3. This is just the density of the displaced air (1.23) minus the density of the aerographene (0.16) minus the density of the hydrogen (0.09). This is almost equivalent to a membrane free helium balloon which means that small and big ballonts are equally viable with the same structure.

As an example, a praying mantis can perhaps be up to 9 grams in weight and 20 cm long. A 13 cm radius sphere of hydrogen filled aerographene would give it neutral buoyancy and it could still flap its wings to move while grabbing food with its forearms.

Keavan said...

The aerographene balloon would presumably contain very little living matter, so it would likely grow either like a horn or a mollusks shell (from the base) or like an antler, from a thin skin around the outside. Either would have interesting ramifications for the structure of the organism in question!

Sigmund Nastrazzurro said...

Keavan and others

I like the idea of graphene layed down on a surface that is then removed. But wouldn't the very thin graphene layer be very vulnerable?