Life in the clouds?

As a lot of people will know by now, the human race is officially going back to Jupiter and its moons. It’s currently scheduled to get there by about 2026. I’m seriously looking forward to it, myself. There’s an awful lot about our friendly neighbourhood giant that we still don’t really understand. In honour of this, I decided to take a look at a classic paper written by Carl Sagan and Edwin Salpeter on the fascinating possibility of life and potential ecologies on a hulking gas giant like Jupiter.

Interestingly, this audacious concept actually dates back to 1975, before Voyager had even made it to Jupiter. An odd thing about Jupiter is that it has a very low reflectivity in the near ultraviolet. The idea Sagan and Salpeter put forward to explain this was the presence of chromophores (complex, light absorbing molecules) in the jovian atmosphere. On Earth, there’s one chromophore which is seen easily across the whole planet. Chlorophyll. It’s interesting to note at this point, that the cause of Jupiter’s striking red colour is still not really understood.

The habitat they went on to describe is not unlike that found in Earth’s oceans. Deep convection currents which stir the atmosphere, from the highest levels down to the deep hot interior. They refer to the lower levels as “pyrolytic depths” — in other words, regions where the temperature reaches over a thousand degrees and any complex organic molecules would literally burn up. The life forms they consider in this bizarre habitat fit into four categories: sinkers, floaters, hunters and scavengers.

The sinkers, they hypothesise, would be the primary autotrophs in the ecosystem, performing photosynthesis and creating the basis for a jovian food chain. These creatures could be responsible for those colourful chromophores. They compare them to plankton in Earth’s oceans, passively sinking through the water until they fall into the darkness and die. On Jupiter though, they’d fall until their environment was too hot, eventually being pyrolysed, burning up in the heat. They calculate that a single celled organism in the jovian clouds would take around 1-2 months to sink. During this time it could reproduce, as plankton do on Earth, continuing the cycle.

But such creatures wouldn’t necessarily have to sink. A creature with control over its internal pressure could learn how to float, in a similar way to fish using a swim bladder to control their depth. Once life evolved such a mechanism, it could take on a predatory lifestyle and evolve into the hunters. Being motile rather than passive, these heterotrophic hunters could survive by eating the sinkers, probably in a similar way to filter feeding creatures (such as krill) in Earth’s oceans.

Finally, the hunters could evolve into floaters, which could be either heterotrophic or autotrophic. With the ability to actively move and control their depth, Sagan and Salpeter explain how these creatures could grow to gargantuan sizes. If such a creature could indeed reach kilometre proportions it would be clearly visible from orbit. While we certainly haven’t seen any evidence for kilometre sized creatures amongst Jupiter’s clouds, the idea alone is a fascinating one.

The final type of creature they mention, which they don’t discuss at great length, are the scavengers. These creatures, presumably evolved from hunters, would inhabit the deep atmosphere, almost at pyrolytic depths. There, they’d feed off carrion drifting down, as deep ocean creatures do on Earth.

The whole paper is well presented, with some in-depth hydrodynamical calculations. While a few facts were unknown at the time (such as the absence of any mesosphere on Jupiter), the idea still looks quite sound to me. It’s certainly worth considering, given the number of Jupiter-sized planets we’re discovering around other stars. But what of Jupiter itself? Could something be lying under the clouds still to be discovered?

Well as I said before, a lot about Jupiter is still unknown. We don’t really understand the convection in the jovian atmosphere, and we can’t narrow down the source of the red colouration. As far as we know, it could be from phosphorus, sulfur compounds (I’d suggest, perhaps S3) or complex organics. Interested, and hoping to fill in a couple of the gaps, I decided to take a look at the chemistry of Jupiter’s clouds.

Jupiter’s atmosphere is enriched in carbon, nitrogen and sulfur. The clouds themselves are made of ammonia, NH4SH and water. In fact the water clouds (the lowest and densest of the three types) seem to hold the bulk of Jupiter’s water, and indeed Jupiter’s oxygen. Being mainly made of hydrogen, Jupiter’s environment is strongly reducing, and most chemicals are hydrides. H2O, NH3, PH3, CH4… The atmosphere above the clouds is also full of haze, thought to be created by the Sun’s UV striking the atmosphere and breaking apart any methane and ammonia molecules carried up above the clouds. This would create a mix of hydrazine, acetylene and PAHs.

The most interesting thing though, is the brief glimpse below the clouds which comet Shoemaker-Levy 9 afforded us. Interestingly, they didn’t find any oxygen-bearing molecules beneath the clouds, but they did find several sulfur compounds. Specifically, S2, CS2 and H2S. The interesting part here is that S2 and CS2 are directly chemically analogous to O2 and CO2 — S2 even has a triplet (diradical) ground state like O2. It’s a rare molecule, actually, having only ever been found in two astronomical objects.

To me, it seems like these chemicals are out of equillibrium with the rest of Jupiter’s atmosphere. They can be reduced further, but due to some process beneath those beautiful swirling clouds, they’re not. Now, I’m not saying that these compounds are evidence for life on Jupiter, but it does make you think…

The joint NASA-ESA mission to Jupiter is set to spend a lot of time exploring Jupiter’s icy moons like Europa, and just maybe we might find evidence of life there. In the meantime, perhaps we shouldn’t write off the possibility that something might be lurking beneath Jupiter’s clouds waiting for us to find it!

Images:
Top: Jupiter’s Great Red Spot (noted by Sagan and Salpeter as potentially a favourable habitat on Jupiter) and the swirling clouds which surround it.

Middle: Benthocodon jellyfish, photographed over 3km below the surface of Earth’s oceans, and a potential morphology for a jovian sinker or floater. ©2002 Monterey Bay Aquarium Research Institute (MBARI).

Bottom: Glass squid, also from Earth’s deep ocean. A jovian hunter might resemble this organism.

ResearchBlogging.orgC. Sagan, E. E. Salpeter (1976). Particles, environments, and possible ecologies in the Jovian atmosphere The Astrophysical Journal Supplement Series, 32 DOI: 10.1086/190414

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
This entry was posted in astrobiology, Imported from Livejournal and tagged , . Bookmark the permalink.

21 Responses to Life in the clouds?

  1. Pingback: Superhabitable! | Supernova Condensate

  2. Anonymous says:

    Re: A bit earlier than that…
    I hope there’s a LOT of inhabited gas giants out there! Would be a boring Universe if it’s populated by “Star Trek” aliens alone.

  3. invaderxan says:

    Re: A bit earlier than that…
    Ok, good point. The concept itself is far older (and was quite pervasive in the works of both Sagan and Clarke) — but this paper is, to my knowledge, the first time Sagan got the chance to formalise his ideas.
    It has to be said, they formalised pretty well. In fact, after reading through the ideas expressed here, I’d be willing to bet that there’s at least one inhabited gas giant somewhere out there…

  4. invaderxan says:

    Re: Don’t forget you can download it online…
    Oh, absolutely. One of the most useful sites on the web!

  5. Anonymous says:

    Don’t forget you can download it online…
    NASA’s ADS has it available for download…
    Particles, environments, and possible ecologies in the Jovian atmosphere

  6. Anonymous says:

    A bit earlier than that…
    Hi InvaderXan
    Sagan speculated on Jovian life back in a 1966 Time-Life book, Planets on the “new” discoveries in the Solar System that he was part of. And we can’t forget “A Meeting With Medusa” by Arthur Clarke, from 1970, which portrayed truly gigantic creatures in the atmosphere of Jupiter. Clarke must’ve been thinking about it in the novel version of 2001 (1968) because he hinted at something in Jupiter’s atmosphere which Poole and Bowman saw as they monitored a drop-probe during the “Discovery’s” flyby on its way to Saturn. He merged 2001 and “A Meeting With Medusa” in his novel version of 2010, as well as reprising the death of the Jovians in 3001.

  7. invaderxan says:

    Attenborough and Sagan… Two of the kings of fascinating documentaries! :D

  8. invaderxan says:

    Well, panspermia could work if life actually formed originally in outer space. Pascale Ehrenfreund has done a fair amount of work in that regard (on nucleobases inside meteorites, for instance).
    In turn, I suppose, if life can form in outer space, it must be relatively easy to form. It’s a harsh environment out there…
    When all’s said and done though, I agree. I’m not holding out hopes of finding life — I just want to see what they find! :)

  9. invaderxan says:

    Re: Astronomy Link List
    :)

  10. invaderxan says:

    Why thank you. :)
    I know what you mean about it being a nice concept for sci fi. And it’s certainly true… We have this assumption about what life needs (i.e. something just like Earth), but as Lovelock pointed out, life actually engineered most of what we see. Sagan was a genius for challenging those assumptions… The world needs more scientists like the two of them!

  11. pax_athena says:

    This was one great entry! The science fiction fan in my head goes all “aww” and thinks how to incorporate this into her stories. While the scientist – well, if taken serious, is it really that improbable that life (whatever it actually is) might have evolved in places different from Earth, whether Jupiter or any other gas giant out there? Earth itself is far from always the most hospitable place…

  12. Interesting.
    I suspect that panspermia wouldn’t work anyways, at least, not from the same source (whether that’s Earth or Mars) as Earth life, given the difference in environment, and there’s no way that life could be ejected from another gas planet, so if there is life on (in?) Jupiter, it would probably have to be a separate origin. So, if it turns out to be so, it’d be a strong argument in favor of life being easy to form which, while the common view among biologists, is far from settled yet.
    Besides, even if there’s no life, that mission should return some interesting data one way or the other. :)

  13. Anonymous says:

    Astronomy Link List
    This article has been added to the Astronomy Link List.

  14. invaderxan says:

    Re: SO2 energy cycle already exists
    Oh, absolutely. There are several habitats on Earth where life metabolises sulfur compounds…

  15. ryttu3k says:

    Sweeet XD I’ll have to see if I can find it! (It definitely wasn’t Blue Planet, though – it was when I was a kid, and Blue Planet came out when I was fourteen. And it started with a boat on a river watching the fireflies, then something with a houseboat, then a red-coloured comb, then more jellies.)
    XD I think it says more about how often I watch Cosmos ;)

  16. Anonymous says:

    SO2 energy cycle already exists
    And of course from earth’s deep ocean vents we can see that the SO2 energy cycle can support life.

  17. invaderxan says:

    No kidding!
    Though I’m not sure if anyone’s considered abiogenesis on ice crystals or cloud particles. The total surface area available across the entire planet Jupiter is probably unimaginably vast!
    As for panspermia though, Jupiter’s upper atmosphere does contain CO2 and CO, thought to have come from comets (there’s no easy mechanism for it to get there from the lower atmosphere).

  18. invaderxan says:

    Ooo… for bioluminescent deep see things, there’s an episode of Blue Planet which you might enjoy. :)
    And hey, what can I say? There aren’t many papers which I’d call “classics”, but the fact thaty you recognise this one pretty much says it all!

  19. If it turns out that Jupiter does have life, that’ll be some really, really, interesting stuff! Especially since the most promising theories of abiogenesis on Earth require solid rock, so either there’d have to be some form of panspermia (which is questionable – how would any microbes get off the rock into the clouds before being burned up?) or some completely different process involved.

  20. ryttu3k says:

    First off, that’s a gorgeous-looking jellyfish! I love jellyfish (and comb jellies), particularly the deep-sea ones (box jellyfish and irukandji = DO NOT WANT D: ). I saw a David Attenborough show on bioluminscant jellies, once – I can’t remember that show it was (I thought it was The Trials Of Life, but apparently not! MIGHT have been a repeat of The Living Planet), but I’ve liked them since then XD
    Also, *grin* I knew this was going to be about that paper as soon as I saw the subject line XD
    Now, I have a biology lecture to listen to XD

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