Jovian Life: The Moons Versus the Planets: Part One

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.

If you are a professional scientist interested in astrobiology (exobiology), searching for life in the Universe, your mantra is “follow the water”. If you want to find life, find liquid water first. But liquid water isn’t the total be-all-and-end-all when it comes to finding LGM – Little Green Microbes. Water, based on Planet Earth’s own terrestrial life as the only statistical sample we have, is certainly critical, but so to are lots of other things as we shall soon see.

Astronomy textbooks written until around or about the 1970’s gave little shrift to the Jovian system as an interesting place to look for extraterrestrial life. The Jovian planets and moons were obviously outside the solar system’s habitable or Goldilocks zone, of which Planet Earth was square in the middle of. My how times change, because, following our robotic exploration of the outer solar system, that point of view has had to partly fly out the window, at least with respect to three pieces of Jovian real estate – the moons Europa, plus Titan and Enceladus (orbiting Jupiter and Saturn respectively). Actually Titan is only really interesting from a pre-biotic perspective. While rich in organic molecules/compounds, it’s considered way too cold for really active chemistry and biochemistry to take place. Titan froze before life could actually grab hold. It lacks a viable energy supply, one of the key items required for life-as-we-know it.  

Alas, the parent bodies, including those gas giants further out (Uranus and Neptune) continue to be overlooked as habitable abodes for ET. The logic of this escapes me as we shall soon see, for the idea that the Jovian planets could in theory harbour life forms as complex as jellyfish or other quasi-aquatic life forms even up to and including the equivalents of Jovian dolphins and whales can’t be ruled out. While Jovian extraterrestrial intelligence (ETI) might be possible, Jovian ETI with technology can pretty much be ruled out, and for much the same reason as to why dolphins and whales here on Earth aren’t a technological species - they can’t build things in the environment to which they have adapted to.

So what’s needed to build us an ET? Well, minimum requirements are 1) appropriate life-as-we-know-it chemicals (CHON – Carbon, Hydrogen, Oxygen and Nitrogen – and of course water or water vapour); 2) a proper comfortable environment for life-as-we-know-it (an appropriate temperature range for liquid water or water vapour); 3) mixing that brings the various inorganic and organic chemicals required into proximity; and 4) an energy source(s) to drive things along, like solar energy does for many terrestrial organisms on Earth.

Mars, though not part of the Jovian system, has been associated with extraterrestrial life for over the past century and then some. That association remains to this very day. Mars is still the poster-boy and remains the prime target in the hunt for ET – even though that association has suffered a downgrade from Martians with ray-guns (as in “The War of the Worlds”) to Martians as microbes – though a microbial ET is just as significant a discovery as a Martian pointing a ray-gun at you. The principle is the same; otherwise it’s just a matter of relative biological complexity. 

Europa (Moon of Jupiter): Science fiction writers can sometimes really hit the proverbial nail on the proverbial head. Take Arthur C. Clarke’s “2010: Odyssey Two” (1982) and “2061: Odyssey Three (1988). Clarke had aliens taking an interest in the primitive life forms under Europa's ice. They transform Jupiter into a star to kick-start their evolution. Fifty years later, Europa has become a tropical ocean world from which humans are banned. Well, the aliens, transforming Jupiter and the tropical ocean are flights of fancy, but the primitive life under the ice of Europa might be something else yet again.

Actually Clarke was tipped off by the two Voyager space probe flybys in 1979. The data and images that were captured strongly suggested to scientists that Europa had to have a salty ocean, perhaps a hundred kilometers deep, but an ocean underneath a vast ice sheet, perhaps up to ten kilometers thick. The energy source was tidal friction, the endless to-and-fro tugging via gravity on the moon by Jupiter and Europa’s companion sister moons. The flexing heated up Europa’s interior, and as heat escaped upwards, melted the covering of ice. The freezing temperature of outer space (Europa has no atmosphere to speak of) freezes the surface which then insulates the heated ocean below from further freezing.

So, you have water, an energy source, mixing, and given the water is in a liquid form, you apparently have a suitable habitat for life-as-we-know-it, well sort of. There’s not going to be any photosynthesis, not that far out and sunlight is not going to be very effective in any event after penetrating kilometers of ice. Translated, the oceans of Europa are going to be pitch-black. The analogy with terrestrial biology is life in our marine hydrothermal vent communities – life driven by Earth’s interior heat and the venting of various chemicals from beneath the ocean floor, and chemosynthesis instead of photosynthesis. Europa’s interior composition mirrors the terrestrial rocky planets – iron and silicates and stuff like that. What is less certain is whether there are abundant sources of carbon and nitrogen.

The one really interesting feature we can see on Europa’s surface is numerous streaks of pinkish-red lines and markings. The source is probably upwelling of the waters below as the surface ice rotates and cracks, sort of like ice floes in our polar oceans. There are lots and lots of organics with pinkish-red colors, though organic chemistry doesn’t of necessity mean biochemistry. Still, perhaps examples of Europa’s life (probably microbial) lie as frozen fossils on the surface. That pinkish-red stuff would be prime material for sampling when and if a probe lands on Europa. In conclusion however, the C and the N in the CHON is the big question mark IMHO.

Enceladus (Moon of Saturn): Europa has competition in our local solar system’s ‘where are the aliens?’ extraterrestrial life debate. We move now from the fifth to the sixth ‘rock’ from the Sun. In 2005 the Cassini spacecraft performed several close flybys of the moon of Saturn, Enceladus, revealing a water-rich plume venting from the moon's South Polar Region. This discovery, along with the presence of escaping internal heat and very few (if any) impact craters in the South Polar Region, suggests that Enceladus is geologically active today. The water vapor spewing from Enceladus's surface would indicate the presence of liquid water immediately under the surface of the moon, which, using NASA’s mantra of “follow the water” might make it possible for Enceladus to support life. The presence of liquid water under the crust means there has to be an internal heat source. That heat source is actually sources, a combination of radioactive decay and tidal heating as tidal heating alone is not enough to explain the amount of heat required.

So the data from instruments on the Cassini spacecraft produced evidence of what’s now termed cryovolcanism - cold volcanism - where water and other volatiles comprise the ‘molten’ stuff that gets erupted from these cold ‘volcanoes’ instead of molten iron and silicate rock – like terrestrial lava that is erupted from our own hot volcanoes.

These cold volcanic eruptions – basically ejections of vapor clouds into space - have been, as noted above, discovered on Enceladus. The detailed composition of these gas clouds are in the main mostly water vapor, plus some other minor volatile components like molecular nitrogen, ammonia, methane, and carbon dioxide. Additional observations have revealed further chemicals in the plume, including both simple and complex hydrocarbons such as propane, ethane, and acetylene. These chemicals and their relative abundances are similar to those seen in many comets. Perhaps Enceladus was once a super-giant comet that got captured by Saturn’s gravity!

All up, these findings raise the possibility for the existence of potential life forms existing beneath the surface of Enceladus. The composition of the gas cloud plume strongly suggests that its source is a subsurface salty ocean or subsurface caverns filled with salty water. Enceladus is therefore a prime candidate for those wishing to investigate non-terrestrial sites harboring potential extraterrestrial life. We have CHON, energy sources, an appropriate temperature regime underneath the surface, and probable mixing, since liquid water facilitates mixing.

Titan (Moon of Saturn): I’ve already noted that while Titan is fascinating from an astrobiology point of view, that point of view is from those interested in pre-biotic organic chemistry that leads to biochemistry, not those hopeful of actually seeing things wiggle. Translated, while it has the CHON, and probably mixing, that’s just about it. The environment is way too cold which suggests that energy available to drive biology is in pretty short supply.

To be continued...