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The possible population of atmospheres of the giant planet
and the acid clouds of Venus – by the protozoans – is frequently written about.
However, the conditions on the planets of the Solar System are too harsh. It
is more interesting to consider a hypothetical planet – with moderate temperatures,
oceans and even an oxidizing atmosphere. And let’s assume that the density of
its atmosphere exceeds the Earth’s one by 100 times.
This assumption, by the way, is quite non-trivial. It’s not too clear where to get enough nitrogen from, so more affordable carbon dioxide is likely to be the basis of the planet’s atmosphere. Accordingly, there will be a powerful greenhouse effect. But if you place the planet at a reasonable distance from the sun, it will only benefit.
Nevertheless, the assumption deserves to be made, because it generates a special world, fundamentally different from the earthly one, in which a hydrogen-filled balloon capable of lifting a human will have a diameter of only one meter. And this means that the flying jellyfish, beloved by science fiction writers, will have the right to exist. Aerostatic flight will become the most obvious and effective way of movemet, quite accessible even for creatures with hard shells.
In a world where air is only 15 times lighter than water, flying cavities in animal bodies will be as common as swimming bladders in fish. But of course, plants will be the first to take advantage of aerostatic flight. If the stem filled with light gas does not weigh anything, then its height is practically unlimited. The tree can stretch upwards for hundreds of meters, and even for kilometers, to raise its crown, made not of flat leaves, but of bubbles, above the clouds. After all, a dense atmosphere reluctantly transmits the light necessary for photosynthesis.
Like algae, the trees of such a planet will keep an upright position due to the lifting force of gas bubbles, and not due to the rigidity of the trunk. The floating branches will be connected to the root system by a strong and flexible harness having minimal windage and able to withstand a hurricane. Although, there should be no conditions for the occurrence of storms on such a planet, since temperature differences are small. But the density of the air compensates for the low speed of movement of atmospheric masses.
If it is difficult to hold on to the soil, then why not leave it forever? Water can be extracted directly from the air by spreading a web of roots, as some orchids do. However, the plant will have to extract the necessary minerals from rainwater and dust. But terrestrial lichens are quite content with these sources. Here, the “prey” will be much more abundant. After all, small particles of wind-blown soil and ash effluented by volcanoes will deposit in a dense atmosphere almost as reluctantly as mud in water. The flying tree will only have to draw in the grains stuck to the leaves, transport them by streams of sap into the “reactor”, and dissolve them, as the mentioned lichens do.
It is possible to imagine greenish clouds of unicellular plants floating in the atmosphere of the planet, but not on droplets of fat, as in the sea, and on bubbles of hydrogen or methane, or simply gliding like little spiders do on their webs. Or there are whole flying islands – colossal carpets of intertwining hollow stems and leaves trailing in the wind. At sunset it is better not to stand under such a drifting crown, because it is not profitable for plants to carry the accumulated dust for a long time. The slag, from which everything useful has already been extracted, must be discarded. It is more reasonable to get rid of the ballast when the sun, which heated the shell, has set, the gas cools and the lifting force decreases.
Animals will also have to adapt to life in a dense atmosphere. On the one hand, the environment creates a lot of resistance to movement, and on the other hand, it does not provide sufficient support. It is too difficult to run, and it is still impossible to swim. Of course, insects can glide on tiny planes, in the hope that air currents will bring them to food. Large creatures will have to invent something original.
Everyone will have to fly. Even if the surface of the planet is not covered by a bottomless ocean and is not overheated – in fact, it turns into the “bottom” of the air sea. Biomass is created in the atmosphere, at an altitude where there is enough light for photosynthesis. It will be consumed in the same place. Those who didn’t take off will get only the leavings.
The optimal solution for these conditions will be a streamlined fish-like creature, 90% of whose body volume will be occupied by gas-filled cavities. Fins can be useful, rather, as rudders, and the jet “engine”, like at squid, is preferable. The size of the creature can range from large to colossal. After all, when swimming in the air, as well as when swimming in the sea, the mass of the animal will be limited only by available food resources. The most important is, that gigantism improves the ratio of mass to the surface of the body, which is very important for an almost “hollow” creature. The larger it is, the easier it is for it, for example, to afford the replacement of soft coverings with hard calcareous armor, impervious to gas and impregnable to enemies. Finally, the flying sperm whale will be ten times larger than the sea-dwelling one, just because it is inflatable.
It will not always be convenient for medium-sized animals to acquire aerostatic organs. A hydrogen bubble will reduce speed and maneuverability, especially vertical one, unless you blow it off completely when diving. This means that flapping wing flight and gliding will remain common modes of locomotion.
Indeed, the pressure will drop with altitude. At twenty-five kilometers from the surface, it will already be only ten atmospheres. There may be winds here – quite strong ones, but a creature carried away by a mass of air will not feel them and, moreover, does not risk run into an obstacle. The area is good for plants; less water and dust, but greater amount of light. If it’s cold, the dark covers, heated by the sun’s rays, will help.
The main thing is that it is more difficult for gliding insects and levitating herbivores to get here. The creature weighing a kilogram will have to be a bubble with a diameter of two footballs. The cavities will already occupy 99% of its volume. For a plant, such a structure is acceptable. For an active and complicated being, it is unlikely. At a higher altitude – up to fifty or sixty kilometers – “living gliders” with impressive planes and arthropods on cobwebs can only fly for a while. However, nothing will prevent both of them from resting and even settling on floating trees.
Translated by Pavel Volkov, 2021
The original Russian article is here