Jovian Life: The Moons Versus the Planets: Part Three

In our solar system, the planets are divided between the inner terrestrial planets (Mercury, Venus, Mars and of course the Earth) and the outer gas giants, collectively called the Jovian planets (after Jupiter, but including Saturn, Uranus and Neptune), which along with their many moons form the Jovian system. Since it’s easier to look in our own planetary backyard neighbourhood first for alien life, there’s been much speculation about what pieces of solar system real estate, if any, might be suitable abodes for extraterrestrial life. While Mars has always been top-of-the-pops, a once heavily favoured Venus fell by the wayside a while back, only to be replaced with a few bits of real estate somewhat further out. It’s those “somewhat further out” bits of real estate that are now under-the-gun. While most speculation is on selected Jovian satellites, I put the accent on the parent bodies.

Continued from yesterday’s blog…

Uranus: CHON: Uranus is similar in atmospheric and chemical composition to Neptune (see below), but both are slightly different in their chemical composition than their larger gas giant sisters, Jupiter and Saturn. As such, astronomers sometimes place them in a separate category called the "ice giants" because these planets contain a lot of – wait for it – “ices” like water (the O in CHON), ammonia (the N in CHON), methane plus other hydrocarbons (your C and your H in CHON) that includes ethane, acetylene, methylacetylene, and diacetylene. In short, instead of say liquid water vapor, you have ice crystals. Uranus's atmosphere is however similar to the “gas giants” in having the majority of its stuff consists of hydrogen and helium, hence followed by methane (there’s some more of your C). Even more C is present in carbon dioxide and carbon monoxide which has been detected. While carbon consists of only about 3% of the composition of Uranus, that’s still vastly more carbon relative to the solar percentage, so Uranus has been enriched in carbon.

Uranus: Environment: Uranus (as well as Neptune), are often refereed to as the “ice giants” instead of the “gas giants” as noted above. One other distinction is that relative to Jupiter and Saturn, Uranus (and Neptune) are way smaller in volume. That apart, the “ice giants” are way more akin to the “gas giants” than to any of the Jovian moons or any of the terrestrial planets for that matter, both in terms of composition and in terms of relative volume. While pretty god-awful from a human’s perspective, some hardy microbes might love to call Uranus home.

Uranus: Mixing: Any lump of gas molecules, or molecules in a liquid, almost by definition, isn’t going to sit still, unlike say the molecules in a lump of rock. A puff of smoke emitted into Earth’s atmosphere gets dispersed; a drop of ink plonked into a bowl of water will equally get dispersed, or mixed in and throughout.  I’d expect nothing less in the non-solid soupy atmosphere of Uranus. In any event, wind speeds have been clocked at up to 900 km/hour – that’s pretty breezy!

Uranus: Energy: Uranus radiates just ever slightly more heat than it receives in the form of solar radiation. In case you think that makes Uranus frigid through-and-through, you’d be wrong. The interior core temperature still approaches over ten to twenty times the maximum temperature of your average home oven! So, while solar energy is just about zilch, energy percolating upwards nevertheless is present for utilization by the locals – if any. However, of all the four Jovian planets, Uranus is probably the least likely planet to have achieved the distinction of harbouring local (Uranian) life forms.

Neptune: CHON: Neptune’s atmosphere is mainly, as you’d expect one that consists mainly of hydrogen and helium, but with substantial amounts of water, ammonia and methane. CHON is present, as are various sulphide compounds.

Neptune: Environment: While the top of the atmosphere is very cold, as you’d expect being so far out from the Sun, the interior core is hot indeed – many thousands of degrees hot. Obviously, somewhere in-between, you’ll get a happy Goldilocks medium as far as biology is concerned.

Neptune: Mixing: Neptune has lots of varied weather and storm systems, all contributing to atmospheric mixing. The temperature differential between interior temperatures and the atmospheric ‘surface’ temperatures, like on Earth, will drive wind systems leading to mixing of the chemicals that make up the CHON-rich atmosphere

Neptune: Energy: Despite being farther away from the Sun than Uranus, Neptune radiates quite a bit more heat than it actually receives from Sol. In fact, slightly over two and a half times more heat. From the point of view of this analysis, the exact reason(s) aren’t overly relevant, just the fact that it does so. Of course being so very, very far away from the Sun there’s no chance in hell of photosynthesis; chemosynthesis is possible, even probable.

In conclusion, I suggest that the soupy atmospheres of the giant planets have all the fundamentals required not only for the origin of life, but long-term habitability for any biological organisms that have been and are being provided with appropriate CHON, a Goldilocks environment (at least in places), an energy supply, and mixing. The CHON box is ticked on all four Jovian planets. With respect to CHON, there are probably all sorts of way more complex organic molecules present in the four Jovian atmospheres but in such relatively small quantities that are dispersed widely and deeply so as to have escaped detection to date from our relatively faraway fly-by and orbiting probes. The habitable environment box on all four Jovian planets is also ticked; ditto the mixing box; and ditto the available energy supply box. You also have had over four and a half billion years for interesting biological happenings to have occurred. In addition, there’s a lot of volume in each of the Jovian planets for interesting stuff to happen in. The odds of things all coming and getting their act together in a small pond is small relative to a large ocean.

That all four Jovian planets have evolved life is problematical; that at least one has become a biological abode is much more certain, IMHO. Throw in one or more of their satellites like Europa and Enceladus that offer a liquid water ocean environment – well that’s a bonus. On top of all that, the Jovian planets have the highest gravities apart from the Sun. Now that means they suck in more than their fair share of other solar system debris – like comets and asteroids. Now comets and asteroids, the leftovers of that initial stuff out of which our solar system was made, also tend to be rich in CHON. No doubt they, via impacts with the Jovian planets, have contributed their CHON bit to the already potential suitability of those abodes as habitable abodes.

So what sort of Jovian life might we expect? On Planet Earth there is a sharp boundary between the atmosphere and the hydrosphere. On the four Jovian planets one just slowly merges into the other as one goes deeper and deeper. Terrestrial but airborne microbes, bacteria, germs, and other single-celled beasties, and their marine equivalents, like plankton and other unicellular critters, occupy both environments and are happy little campers. There’s no reason for there not to be Jovian equivalents that ‘swim’ and multiply in whatever region of the various four varieties of Jovian atmospheric ‘soups’ that have a comfortable, Goldilocks temperature regime. Of course that Goldilocks region could extend over hundreds of vertical kilometres in range. Some organisms might be better adapted to the thinner cooler upper regions; others to the murkier but warmer depths. Regardless, it gets dark fast so eyesight in the visible range of the electromagnetic spectrum might be problematical. Of course phosphoresce, not all that uncommon in marine life here on Earth, can’t be ruled out of course.    

If simple life forms originated and evolved on Jupiter, Saturn, Uranus and/or Neptune, then more complex and far larger ‘marine’ and ‘aerial’ life forms might be present too. Their trick, in order to stay in the Goldilocks zone, will be to have evolved the capability to maintain neutral buoyancy, but also to be able to rise if turbulence pushed them downwards towards greater heat; be able to sink if currents push them too high where chill factors come into prominence. So ‘gas bag’ floaters or ‘fish’ with ‘airbags’ might be possible Jovian alien life-forms. There’s no reason such critters couldn’t have developed a relatively sophisticated degree of intelligence. It’s possible to have intelligence without the means of developing technology as our whales and dolphins and even the humble octopus demonstrate.

The fly in the ointment is that our on-site investigation is going to prove to be an extremely daunting technological task, one that most certainly won’t happen in the next several decades – probably much longer. In the short term, the best bet is to use remote spectroscopic analysis of the atmospheric ‘surfaces’ or actual surfaces (in the case of the satellites) to identify biological signatures – compounds that just cannot be accounted for by non-biological processes. An example would be the pinkish-red areas on Europa noted above.