It’s 1980. The decade of the 70’s has come to an end, and with it, a time when space travel seemed to be achievable just in a few decades. Fueled by Apolo’s XI landing in 1969, science fiction had just experimented a sudden rise that had even been promoted to the mainstream media (Star Trek, Star Wars, The Andromeda strain…), opening questions about space travel and extraterrestrial life.It is in this context that the famous series Cosmos: A Personal Voyage, one of the most influential pieces of popular science, airs. Throughout the series, the astronomer, astrophysicist and science writer Carl Sagan, marvels the audience with explanations about life and the universe.

In one of the episodes, deeply influenced by the events of the last decade, the scientist asks a bold question: how would life on Jupiter be like? This is, of course, an outlandish question which some scientist would surely consider somewhat farfetched. What not so many people know, though, is that this was not a mere resource to draw the attention of the public. In fact, it was part of a scientific exercise published by Sagan and Edwin E. Salpeter, an astrophysicist from Cornell, in 1976. The paper, entitled Particles, environments, and possible ecologies in the Jovian atmosphere presents a series of scientific imaginary creatures, theoretical inhabitants of Jupiter.

The main question regarding life in Jupiter is how to survive in a planet made out of mainly gas (we would not recommend to live in the extremely pressured nucleous). The answer is simple: the Jovian fauna would consist of floating organisms that would survive in the inhabitable layers of the atmosphere. Sagan draws a parallelism between this theoretical ecosystem and the marine planktonic communities. In this type of community, the primary producers (mainly algae and bacteria) remain in the sunny layers of the water column. Through decay or transport via marine currents, these organisms (or their remains) end up in lower parts of water column, feeding the remaining trophic chain.

The Jupiter ecosystem would funcion in a similar way, but with different actors. The actors of this Jovian ecosystem are as follows:

Sinkers

Sinkers would be small organisms unable to remain stable in the upper parts of the atmosphere, slowly sinking to the center of the planet or following the planet’s wind currents. Their lifestyle would be similar to that of bacteria or some protozoa: fast life cycles and the ability to cope with harsh environments, either through specializations in the membrane… or by a form of cryptobiosis. And what would they feed on? One option is that these organisms would be photosynthetic, absorbing the light of a distant Sun using their chromatophores. The second option would be for them to be heterotrophs, capturing organic molecules present on the atmosphere (according to the authors, some molecules, like ethane, could be present as a photoproduct of Jupiter’s methane).

Floaters

Floaters would have an intricate system of floatability. This floatability would be acquired thanks to the absorption of pure hydrogen, which would present a lower molecular weight than the combination of hydrogen and helium present in the atmosphere or by heating internal hydrogen using metabolism derived heat. In order to accomplish so, the authors calculate that floaters could reach sizes of kilometers (and thus being observable by the Mariner Jupiter/Saturn, a spacecraft program that would eventually become the Voyager missions). So, basically, floaters would be city-sized balloons of hydrogen.

In a similar way to Sinkers, Floaters would be photosynthetic, using either methane or ammonia as electron donors. The alternative would be, once again, for them to absorb organic molecules via passive diffusion. Although the sight of such organism would certainly be jaw-dropping, Sagan and Salpeters also point out that with known cell structures, these organisms would be as stable as a bubble.

Hunters

Hunters are the fishes of this system, primary consumers that float thanks to specialized structures while surfing the Jovian atmosphere for prey. They could also reach gigantic sizes (and again, the authors point out how could they be observed by the Mariner Jupiter/Saturn missions).

Scavengers

Scavengers are the type of fauna that we would find in the benthos of the marine ecosystem: organisms in the deep layers, many of them which depend mainly on dead organisms or residues of organic matter. Scavengers would behave in a similar way to Floaters, but would certainly not be photosynthetic.

Life on Jupiter

But Jupiter is not exactly a mild environment, temperatures can reach up to 600ºC, pressures up to 10⁶ Pa, winds about 100 m/s and the atmosphere is strucked by huge thunderstorms. Actually it is difficult to think about any organic molecule surviving under those conditions (and currently the possibility of life in Jupiter is thought to be almost negligible). In fact, Sagan and Salpeters define an atmospheric layer where organic matter could not be present, which they term “pyrolythic depth”.

Falling to the pyrolythic depth would be a huge selective pressure for the inhabitants of Jupiter. Floaters, scavengers, hunters and specially sinkers would need to complete their life cycles before falling to these layers. One important part of this life cycle involves, of course, reproduction. The authors propose a type of reproduction involving dispersules (which for biology standards, could be similar to fission or budding), which would only be possible after a fussion of two or several individuals. Interestingly, the authors also propose that hunting would work in a similar way, where Hunters would clash against the prey, making “the distinction between hunting and mating under these conditions (is) not sharp”.

Particles, environments, and possible ecologies in the Jovian atmosphere is mainly an astrophysical paper, though, and not much more detail is explained about the ecology or biology of these organisms (there is though, much more to read about atmosphere composition and structure, photoproduction…).

So, what does this entry of The scientific imaginary creatures tell us? It is clear that such organisms do not exist, but this exercise does something that it is indeed remarkable: it ties up completely different disciplines and creates an scenario where imagination and the limits of biological life are put to the test.

Adolf Schaller was responsible for portraying these imaginary animals in Cosmos: A Personal Voyage. You can find the story of this process here. The images of this article are personal drawings (yes, I still have more to learn) based on Schaller’s portrayals (with the exception of the Scavengers, a personal creation).

Bibliography

Sagan, C., & Salpeter, E. E. (1976). Particles, environments, and possible ecologies in the Jovian atmosphere. The Astrophysical Journal Supplement Series, 32, 737-755.

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In the next issue of Onelephantsandbacteria… we celebrate April’s fools day (later, but never mind) with the Rhinogradentia, the ultimate work of fictional animals.