Thursday 10 September 2020

Ballonts VIII: Blue Sky Thinking (Part 1)

By Abbydon

Over the past few years, I have discovered an interest in astrobiology as it combines my childhood fascination with both astrophysics and biology. Linked to this I also enjoy speculative biology though sadly my artistic talents are embarrassingly poor (For reference, I did not produce any of the pictures shown below). For this reason, I have followed the various articles on lighter-than-air organisms (also known as ballonts) with interest.

Like many other people, I have found it disheartening that designing a plausible small ballont has proven challenging. Large ballonts appear to be viable as they can generate sufficient lift to allow both the balloon and a body to float but smaller ballonts cannot get off the ground.

This is unfortunate as it means infant “large” ballonts would be unable to float until they had grown sufficiently large. Small ballonts are also interesting as they can form only part of an organism’s lifecycle which may allow the body to have reduced functionality. This could be a mechanism for spore dispersal from an otherwise sessile organism as a more sophisticated version of a dandelion clock. Alternatively, it could be for reproduction only like an adult mayfly which can have a life measured in minutes.

As previously discussed on this blog, the problem for small ballonts is the membrane needed to contain the lighter than air lifting gas. A small volume of lifting gas without a membrane would of course float but it wouldn’t take anything with it. Therefore, clearly a membrane of some form is needed to separate the lifting gas from the rest of the atmosphere. Unfortunately, the mass of the membrane is proportional to the surface area of the ballont whereas lift is proportional to the volume. Since all membranes have mass this means that for small ballonts the mass of membrane is typically greater than the lift produced by the lifting gas.

Solving this problem requires reconsidering what could be used as a membrane in an attempt to get closer to the “magic massless membrane” than Mylar. Mylar is used for long lived helium party balloons and has a thickness of 0.1 mm with a density 1.2 times water, which is perfectly adequate for large ballonts but insufficient for small ones.

Two possible ideas sprang to mind which might achieve this, the first of which will be discussed in this article, with the second reserved for a following article. The first possibility to be considered is whether soap bubbles could be used. There are many videos online showing lighter-than-air hydrogen filled bubbles being produced, though they do normally come to fiery end which is not what we want to happen to our poor ballonts.

Soap bubbles may not seem the ideal form for a ballont but a bubble film is typically around a thousandth of a millimetre thick and has a density of approximately water. This is much closer to a massless membrane than Mylar so perhaps it will enable smaller ballonts. A ballont would not literally use soap to produce bubbles but would instead use some alternative organic chemical.

In previous articles a hypothetical Mylar based ballont was shown to float only once its radius was above 30 cm but the chart below shows that a hydrogen filled soap bubble could provide lift at much smaller sizes. For reference,


Click to enlarge; copyright Abbydon
However, while the Guinness world record for bubble size is just under 100 cubic metres we don’t expect plausible ballonts to use single bubbles that large. The next chart shows smaller hydrogen filled bubbles can still lift a few milligrams if they have a radius larger than 3 mm.

Click to enlarge; copyright Abbydon
Scientists are known to do strange things in the name of Science but perhaps one of the weirdest papers I have read involves weighing 90 leaf cutter ants to determine their load carrying performance. Apparently they ranged from 1.2 to 36.8 mg with an average of 9.3 mg. The extreme low end of this is light enough that it could be lifted by a single bubble with about a 7 mm radius. Perhaps an alien leafcutter ant could generate a bubble to get to the top of a tree, harvest a leaf and use the ballast to descend once again. Such an “antballont” might look like a honeypot ant with a bubble for an abdomen as shown in the sketch below.

Click to enlarge; copyright Gert van Dijk. The squares are 1 mm in size. The panel on the left shows a circle with a 7 mm radius and a small leafcutter ant. the panel on the right shows an evolved ant holding a bubble between its hind legs.  

A single bubble could be viable for tiny ballonts such as the ant but it would be too fragile for large ones. A better solution for larger ballonts would be to produce a foam of many small bubbles. Each of these bubbles would produce lift on its own and a foam mass would produce more. This approach has been used to generate floating helium filled foam letters for advertising purposes!

The chart below shows that such a foam mass produces less lift than a single bubble of the same volume but a 5 cm radius spherical foam mass of individual 0.5 cm radius bubbles could still carry just over a quarter of a gram. This again sounds light but it could certainly carry a bundle of seeds or an insect several times larger than an ant. It is probably even enough to carry a vertebrate such as the 7.7 mm long frog, Paedophryne amanuensis with its legs spread out to stay in contact with the bubbles.

Click to enlarge; copyright Abbydon

This all suggests that the soap bubble idea is valid for producing a somewhat plausible small ballont without too much hand waving. This is possible because of the thin water-based membrane but there is one important disadvantage, a short lifespan. The bubble will pop eventually unlike a solid membrane. This can be managed if the ballont does not need to remain aloft indefinitely, perhaps because it is only part of a lifecycle (e.g. a seed or a mayfly) or perhaps because it only creates the foam to float at night. Alternatively, the organism could regenerate the bubbles constantly while in flight to maintain and even adjust lift.

How long can a bubble last though? About a hundred years ago, in a sealed container it is claimed that Scottish scientist James Dewar 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. This is not likely under realistic conditions but it shows what is possible.

Bubbles burst when the membrane becomes too thin as the water in the membrane flows to the bottom of the bubble or it simply evaporates. While low temperature and high humidity conditions may enable bubbles based ballonts to last longer, a more feasible approach is to add chemicals to the bubble mixture to make the membrane more resilient. For fun at home the Soap Bubble Wiki has several recipes for this.

It remains an open question as to how long a bubble foam could last but several minutes is possible with these home-made bubble mixes. Some species of frogs and fish make bubble nests that last for days, however, these require maintenance and might be too heavy to float. It is therefore conceivable that a biologically possible option in between these two extremes could produce a bubble foam that would be light enough to float but had a longer duration than normal. This would be ideal for seed, spore or larva distribution where a 5 cm radius foam containing a few hundred bubbles could be generated by the parent before being sent on its way to pastures new. This is shown below with the small Furahan “brochos” larvae suspended in a floating foam to enable longer range travel than would otherwise be possible.

Click to enlarge; copyright Gert van Dijk. This is a sketch for a painting that has already been finished and will appear in The Book.

Click to enlarge; copyright Gert van Dijk. The Book will contain many secondary illustrations; this one will accompany the one above.
This article will be concluded with a discussion of the alternative option to soap bubbles for small ballonts. Please let us know what you think of soap bubble ballonts by commenting below.

Since people seem interested in my thoughts on these topics I thought I should perhaps produce my own blog. Since I am a physicist and no artist this will be quite different to the Planet Furaha blog. I have therefore started Exocosm which will discuss the possibilities of planets around other stars (i.e. exoplanets). Time will time whether I can manage to continually produce worthwhile articles though…


This was the first ever guest post on this blog, and I hope you liked it. Abbydon and I decided to split it into two parts; the second one has already been written, but I need to produce an additional illustration before it can be posted. 

If anyone else is interested in writing a guest post, write to me about the idea and do not send a complete text yet!

Sigmund Nastrazzurro 
(nastrazzurro  AT gmail DOT com)


Keenir said...

great article. its giving me some ideas...need to scan in the pic.

Abbydon said...

Thanks. I'm definitely curious to hear what ideas people have in response to this.

Sigmund Nastrazzurro said...

Unknown: I don't think you can add an image to a comment, so you would have to email it,

Keenir said...

anthony docimo here - sorry I took so is a sketch I made up of something tetrapter-ish making foamy bubbles with its legs/arms and grebe-like toes (I figured that whether or not it generates the bubbles from its arms, it could use the arms and toes to build up the lather)

Keenir said...

sorry - link is here:

-Anthony Docimo.

Abbydon said...

I had a look at your pic on Deviantart and replied there a few days ago. I probably should have also responded here. Anyway, it's good to see that the bubble idea has spawned new artwork already. As for how to form bubbles, my young children know exactly which part of their body can produce bubbles when in the bath...

dynamax wailord said...

alphynix on tumblr had a speculative evolution month called "Spectember" and you might be pleased to know Furaha was featured in one of their special weekly events! :)

Keenir said...

can you provide a link, please?

Abbydon said...
This comment has been removed by the author.
Abbydon said...

Spectember Interlude: Furahan Biology

Sigmund Nastrazzurro said...

Anthony: I like your foam bubble beast; do i see it correctly that it has two legs to catch prey and a tail to grab onto branches and the like? By the way, i also like the cheetah-0like hexapod above, using flexion and extension of the spine to increase stride length.

Dynamax wailord and Abbydon: thanks for the notification and the link. It's quite complimentary. One of these days i should update the main site...

Anonymous said...

Anthony says,
my concern with the Foam Bubble Beast was to get the concept onto paper, rather than making sure all the limbs were visible; thats why I didn't take the time to check the radial number of upper or lower limbs, or to draw more than two of either set, in the bubble beast or in the critter flying by.

thank you for the kind words about the cheetah hexapod; I couldn't recall if you'd ever said how flexible (if at all) Furaha's hexapod spines were...{i *think* even Earth mammal carnivores of the Eocene had spines that were as flexible as an antelope's - or less flexible than antelope} i assumed total flexibility, and tried to see if there was a disaster in the making. :)

Keenir said...

also from Anthony:
thats a tail if you want to interpret it as such; though I'd tried to draw it as another limb (no idea why it wasn't raptoral like the other two)

sorry for the confusion

Andrew Broeker said...

It occurs to me that earth's bodies of water already contain several ballonts

Sigmund Nastrazzurro said...

Anthony: Furahan hexapods descended from fish-like ancestors with two lateral stiffening rods to anchor their lateral membranes. Their descendants are largely stuck with this design, and so can bend well up and down, but not sideways. hence, increasing stride length by cyclically bending and extending the body parallel with leg movements would certainly work, I think you could have an extension of the hind legs together with the hind-middle body half. then, when it is the turn on the middle legs, they extend while the middle-front part of the body also does so. Ten the front legs hit the ground, the hind legs will reach far forward and touch down quickly after the front legs, and then the cycle repeats itself. there might be other ways but this seems workable. I hope the explanation makes sense without a drawing.

Andrew Broeker: if you mean swim bladder and similar low-density organs, i agree that these also use Archimedes' principle to prevent sinking. Please have a look at the post 'Ballonts II' from 7 September, 2008, in which I made that same point. However, I doubt many people would want to classify submarines as balloons; even though the physical properties are the same, there seems to be a linguistic barrier.

Keenir said...

I, Anthony, say
I had a thought: perhaps the ballonts aren't working because we're putting them at or near ground level, rather than the layer of atmosphere where there is the most pollen and bugs to eat. (better winds, i think)

Abbydon said...

High altitude "ballooning" certainly works for spiders and is definitely worth considering. However, they are not lighter than air. The maximum body mass possible for a lighter than air ballont is its volume multiplied by the difference in density between the ambient air and the balloon. Since air pressure decreases with altitude then air density decreases as well. This means that ballonts are more feasible in denser air (e.g. venus) and on Earth-like planets this occurs at lower altitudes and/or lower temperatures.

Intriguingly, this means that the pressure in deep mines is greater than at the surface. For example, in a 5km deep mine the air pressure (and therefore density) is apparently 66% higher. I'm not sure that ballonts could be cave animals but this could be of interest on a planet with very large variation in elevation. Ballonts would then be more viable in the lowland areas where the air was slightly denser.

Keenir said...

I, Anthony, say,
Given that they would live that far up, being lighter or heavier than air would be almost moot, because even if they sink for a while before another gust of wind picks them back into higher layers, they are still airborn.

Its like how clouds are constantly falling, and yet they don't touch the ground (normally)

though it *is* an interesting idea, having ballonts in deep-underground caverns and tunnels, maybe feasting on lithovore biofilms. :)

Sigmund Nastrazzurro said...

Anthony: are there in fact more pollen and bugs high up in the atmosphere than there are near the ground? As they are formed on the ground, wouldn't there be more near the ground than high up?
Anything that increases the difference in mass between the atmosphere and the inside of a balloon envelope will help increase lift. A dense atmosphere certainly does so.

The deeper the mine, the more air pressure should rise. However, if the temperature also rises, that will cause the local atmosphere to expand, decreasing pressure.
But even if balloons would work better in an extremely deep mine, there wouldn't be much open space to fly into...