Mythologies of the Solar System: Part Three

The names of the moons, planets and of course the Sun itself are not just household names un-associated with anything but these celestial bodies, but bodies usually named after selected characters from ancient Greek and Roman mythology. There are tales to be told about them; some fleshing out to do. These are just a few of the highlights.

The planets of the solar system are named after gods and goddesses and are known by their Roman, not Greek names. Here I’ll put the Greek equivalents in brackets afterwards. The satellites of these planets for the most part tend to be the Greek names associated in one form or another with the parent body or the god/goddess in question. Moons (and major asteroids) are identified with an asterisk.

Continued from yesterday’s blog…

MYTHOLOGY AND THE OUTER SOLAR SYSTEM

SATURN (Cronus) was one of those first generation Titans, offspring of Gaia and her son Uranus. He mated with Rhea, and produced from that union the original half-dozen gods and goddesses that would eventually become the Olympians. But the transition from Saturn’s offspring to become the rulers of Mount Olympus was an epic that could just about out-epic anything Hollywood has ever done. Saturn is known for two things in particular – castrating his daddy and snacking on his kids - Yum, yum. 

*Dione is a very obscure goddess who may have been a Titan or a Nereid or an Oceanid. Her name seems to be a feminine form of Zeus, and that brings in the alternative version of the origin of Aphrodite – a traditional birth via the union of randy Zeus and Dione (whoever she was). At least she’s now immortalized as a satellite of Saturn.

*Enceladus was one of the Gigantes. The Gigantes were offspring of Gaia, fertilized by the blood/semen of her son and lover Uranus who was ultimately castrated by Cronus (a son of Gaia and Uranus back when he had his private parts intact). In the Gigantomachia (the battle between the Olympian gods and the giants), Athena deposited Enceladus under Mount Etna and the fire and brimstone breath of Enceladus accounts for that volcano’s well, fire and brimstone. This is another abode thought as a possible site where alien life forms might one day be discovered.

*Hyperion was a Titan god, born of Gaia (Gaea) and her son, Uranus. He would become an early god of the Sun.

*Iapetus was another Titan god, born of Gaia (Gaea) and her son, Uranus. He would become the father of Prometheus, who ultimately is remembered for stealing fire from the gods and giving it to mankind.

*Janus was the Roman god of beginnings, doorways, entrances, gateways, etc. and is depicted with two faces, one each facing forward (to the future) and the other backward (to the past). January, the beginning, is named after him.

*Mimas, like Enceladus, was one of the Gigantes of Greek mythologies. Like the other giant sons of Gaia and Uranus, Mimas had serpents for legs and was born fully armored. Mimas was slain by Hephaestus during the war against the Olympians by a volley of molten iron.

*Phoebe was a Titan goddess, born of Gaia (Gaea) and her son, Uranus. Phoebe is identified as an early moon goddess. In another context, the goddess Artemis sometimes was associated with an alias of Phoebe. Finally, Helen of Troy had a half-sister Phoebe.

*Rhea was another Titan goddess, born of Gaia (Gaea) and her son, Uranus. She married Cronus (Saturn) and from that union was born what ultimately became the original half-dozen Olympian gods and goddesses. Cronus, out to eliminate potential future rivals, swallowed the first five of these kids, but Rhea tricked him when it came to the sixth and last, Zeus. She spirited Zeus away to Crete to be raised, and tricked Cronus into swallowing a stone disguised as the baby Zeus.

*Tethys was yet another Titan goddess, born of Gaia (Gaea) and her son, Uranus who would become the most ancient goddess of the sea.

*Titan is the largest moon of Saturn, a moon of interest to astrobiologists, and the only natural satellite to have an extensive atmosphere. In fact, Titan is larger than the planet Mercury and way lager than our own satellite, Luna. The mythology connection is that the original dozen Titans (some of which are named satellites of Saturn) were one of a set of offspring between Gaia and Uranus. Among the second generation of Titans are several household names like Atlas and Prometheus. They were overthrown in the Titanomachy (The War of the Titans) by Zeus and his fellow Olympians. 

URANUS (alternative spelling Ouranos) was the original sky god, the son, via parthenogenesis, of Gaea (Gaia) who shacked up with mum to produce all manner of deities, including monstrous ones. He’s known for having his privates sliced off by one of their Titan offspring, Saturn (Cronus). Saturn in turn got done like a dinner by one of his offspring, Jupiter (Zeus) but that’s another story.

*Ariel, Miranda, Oberon, Titania and Umbriel, the five major moons of Uranus, were named or chosen from the names of characters from the works of Shakespeare and Alexander Pope and thus, unfortunately, have near bugger-all to do with traditional Greek and Roman mythology. Bummer, as that spoils some potentially good stories relating back to and involving the parent god, Uranus.  

NEPTUNE (Poseidon) was the god of the sea, one of the original half-dozen Olympian gods and goddesses, brother to Zeus, Hades, Hera, Hestia and Demeter. All of Neptune’s known 13 satellites are named for Green and Roman water deities or groups of minor water gods. The major two are Nereid and Triton.

*Nereid – the Nereids (plural) were nymphs of the sea, the 50 daughters of the Mediterranean Sea god Nereus. Among the famous of the Nereids – goddess all – were Thetis (mother of Achilles), Galatea and Amphitrite (who married Poseidon). 

*Triton was another sea god, a son of Poseidon and the Nereid goddess Amphitrite, a nymph of the sea who became Queen of the Sea when she wed Poseidon. The typical depiction of Triton is that of a merman – human head and torso; one or two fishy (or maybe dolphin) tails. He too has a trident and a conch shell which when blown can calm the stormy waves. Like father, like son, Triton also had a bit of an eye for the ladies, especially beach-babes. Triton favors in a positive light for assisting Jason and the Argonauts in their saga. 

PLUTO (Hades) was god of the underworld. In the Greek version, Hades (the god) administered Hades (the underworld), so the name of the ruler and the place ruled were one and the same. Within recent times, Pluto was officially downgraded from planet to dwarf planet status, which made a lot of traditionalists very unhappy.

*Charon was the son of Erebus (the god of underground darkness) and Nyx (goddess of night), who played the role of the ferryman who rowed the newly deceased across the River Styx to Hades, the underworld. As a reward, or a fare, he got a coin in payment – no coin, no crossing. The parentage and place of employment are ideal for a satellite so far out from the Sun.

*Hydra (discovered in 2005) was named after that famed beastie slain by Hercules as one of his dozen labors in Greco-Roman mythology. Hydra was one of numerous monstrous offspring from Typhon and Echidna, themselves monsters. 

*Nix (a deliberate alternative spelling of Nyx) was a Greek goddess of night, one of the original deities conceived from the original state of the universe, Chaos. Nyx was the mother of Charon. Like Hydra, Nix the satellite was discovered in 2005.

ERIS is another dwarf planet, a trans-Neptunian object even larger that Pluto discovered in 2005. In fact it’s the most massive of all dwarf ‘planets’ in our solar system, even though it’s three times farther removed from the Sun than Pluto. Eris is a Greek goddess, the personification of strife and discord.

*Dysnomia in mythology is the daughter of the goddess Eris.   

NEMESIS (Fortuna was the Roman counterpart) was the asexual product of the goddess Nyx (night) and she was the goddess of retribution and agent of vengeance. Originally she was just one who dispensed fortune or luck without predetermined rewards or punishments, but morphed into a goddess of justice. The ‘Wheel of Fortune’ is thus associated with her. The celestial Nemesis is a hypothetical dwarf star binary companion to our Sun, a faint stellar object that has an extreme elliptical orbit that beings it close to the solar system once every 26 million years, which when extrapolated backwards, was useful in explaining periodic mass extinctions on Earth. Alas, all searches for this dwarf companion star have turned up negative, and the hypothesis is pretty much in scientific limbo today. 

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...

Exobiology: Bibliography: Part Two

Exobiology was the original term given to the sciences central to the question of life-in-the-Universe. It’s now been largely replaced by Astrobiology, but I’ll stick with the original. To investigate life-in-the-Universe one needs a solid grounding in the relevant literature. A comprehensive relevant bibliography would run to many thousands of pages and be rather off-putting. So, perhaps something on a slightly smaller scale might be more in order to help the novice get started. 

For something that doesn’t yet exist, extraterrestrial life, intelligent or otherwise, has hatched a massive amount of literature, both technical and popular, in English and otherwise. There are speculative books, articles, documentaries, etc. that number in the tens of thousands. Add the sci-fi contributions into the mix, and you have tens of thousands more entries. Here are just a few more samplings of some of the non-fictional monographs that have touched on some of the topics raised so far.

Further Readings: Intelligent Life on the Moon

Leonard, George H.; Somebody Else Is On the Moon; David McKay Company, Inc., New York; 1976: 

Wilson, Don; Our Mysterious Spaceship Moon; Dell, Publishing Co., Inc., New York; 1975: 

Wilson, Don; Secrets of Our Spaceship Moon; Sphere Books Limited, London; 1980:

Further Readings: Our Solar System

Brack, Andre & Clancy, Paul & Horneck, Gerda; Looking for Life, Searching the Solar System; Cambridge University Press, New York; 2005: 

Carle, Glenn C. & Huntington, Judith L. & Schwartz, Deborah E. (Editors); Exobiology in Solar System Exploration; NASA SP 512; U.S. Government Printing Office, Washington, D.C.; 1992:

Horowitz, Norman H.; To Utopia and Back: The Search for Life in the Solar System; W.H. Freeman and Company, New York; 1986: 

Ponnamperuma, Cyril (Editor); Chemical Evolution of the Giant Planets; Academic Press, Inc., New York; 1976:

Further Readings: Mars

DiGregorio, Barry E. & Levin, Gilbert V. & Straat, Patricia Ann; Mars: The Living Planet; Frog, Ltd., Berkeley, California; 1997: 

Goldsmith, Donald; The Hunt for Life on Mars; Dutton, New York; 1997:

Sawyer, Kathy; The Rock from Mars: A Detective Story on Two Planets; Random House, New York; 2006:

Further Readings: Intelligent Life on Mars

Carlotto, Mark J.; The Martian Enigmas: A Closer Look; North Atlantic Books, Berkeley, California; 1991: 

Hoagland, Richard C.; The Monuments of Mars: A City On the Edge of Forever; North Atlantic Books, Berkeley, California; 1987:

Further Readings: Europa & Titan

Greenberg, Richard; Europa, the Ocean Moon: Search for an Alien Biosphere for Life on Jupiter’s Ocean Moon; Springer- Praxis Books, New York; 2005:

Greenberg, Richard; Unmasking Europa: The Search for Life on Jupiter’s Ocean Moon; Copernicus Books/Praxis Publishing Ltd, New York; 2008:

Lorenz, Ralph & Mitton, Jacqueline; Titan Unveiled: Saturn’s Mysterious Moon Explored; Princeton University Press, Princeton, New Jersey; 2008:

Further Readings: The Rare Earth Hypothesis

Brownlee, Donald & Ward, Peter D.; Rare Earth: Why Complex Life Is Uncommon in the Universe; Copernicus Books, New York; 2000:

Further Readings: Extraterrestrial Intelligence

Gould, Stephen Jay; Wonderful Life: The Burgess Shale and the Nature of History; Vintage, London: 2000: 

Morris, Simon Conway; The Crucible of Creation; Oxford University Press, New York; 1998:

Morris, Simon Conway; Life’s Solution: Inevitable Humans In A Lonely Universe; Cambridge University Press, New York; 2003:

Seielstad, George A.; At the Heart of the Web: The Inevitable Genesis of Intelligent Life; Harcourt Brace Jovanovich, Publishers, Boston; 1989:

Further Readings: SETI

Davies, Paul; The Eerie Silence: Are We Alone in the Universe?;

Allen Lane, London

; 2010:

Drake, Frank & Sobel, Dava; Is Anyone Out There? The Scientific Search for Extraterrestrial Intelligence; Delacorte Press; New York; 1992: 

McConnell, Brian; Beyond Contact: A Guide to SETI and Communicating with Alien Civilizations; O’Reilly & Associates, Sebastopol, California; 2001:

McDonough, Thomas R.; The Search for Extraterrestrial Intelligence: Listening for Life in the Cosmos; John Wiley & Sons, Inc., New York; 1987:

SETI Institute Science & Technology Working Group; SETI 2020: A Roadmap for the Search for Extraterrestrial Intelligence; SETI Press, Mountain View, California; 2002:

Shostak, Seth; Confessions of An Alien Hunter: A Scientist’s Search for Extraterrestrial Intelligence; National Geographic, Washington, D.C.; 2009:

Further Readings: Exploration and Colonization of Interstellar Space

Gilster, Paul; Centauri Dreams: Imagining and Planning Interstellar Exploration; Copernicus Books, New York; 2004:

Macvey, John W.; Interstellar Travel: Past, Present, and Future; Stein and Day, New York; 1977:

Further Readings:  The Fermi Paradox

Hart, Michael H. & Zuckerman, Ben (Editors); Extraterrestrials: Where Are They?; Pergamon Press, N.Y.; 1982:

Hart, Michael H. & Zuckerman, Ben (Editors); Extraterrestrials: Where Are They? [2^nd edition]; Cambridge University Press, Cambridge; 1995:

Verma, Surendra; Why Aren’t They Here? The Question of Life on Other Worlds; Icon Books, Cambridge; 2007:

Webb, Stephen; Where Is Everybody? Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life; Copernicus Books, N.Y.; 2002:

Further Readings: Ancient Astronauts

Blumrich, Josef F.; The Spaceships of Ezekiel; Bantam Books, New York; 1974: 

Castle, Edgar W. & Thiering, Barry B. (Joint Editors); Some Trust in Chariots!!; Westbooks, Perth, W.A.; 1972:

Daniken, Erich von; Chariots of the Gods? Unsolved Mysteries of the Past; G.P. Putnam’s Sons, New York; 1969:

Daniken, Erich von; Gods from Outer Space: Return to the Stars or Evidence for the Impossible; G.P. Putnam’s Sons, New York; 1971:

Daniken, Erich von; In Search of Ancient Gods: My Pictorial Evidence for the Impossible; Souvenir Press, London; 1974:

Downing, Barry H.; The Bible & Flying Saucers; Avon Books, New York; 1968:

Drake, W. Raymond; Gods and Spacemen in the Ancient East; Sphere Books, London; 1974:

Drake, W. Raymond; Gods and Spacemen in the Ancient West; Sphere Books, London; 1974:

Norman, Eric; Gods Demons and UFOs; Lancer Books, New York; 1970:

Story, Ronald; Guardians of the Universe?; New English Library, London; 1980: 

Story, Ronald; The Space-Gods Revealed: A Close Look at the Theories of Erich von Daniken; Harper & Row, New York; 1976: 

Temple, Robert K.G.; The Sirius Mystery; Sidgwick & Jackson, London; 1976:

Wilson, Clifford; Crash Go the Chariots; Lancer Books, New York; 1972:

Wilson, Clifford; The Chariots Still Crash; Signet, New York; 1975:

Wilson, Clifford; The War of the Chariots; S. John Bacon, Melbourne, Victoria; 1978:

Exobiology: Life in the Solar System: Summary & Conclusions

Exobiology was the original term given to the sciences central to the question of life-in-the-Universe. It’s now been largely replaced by Astrobiology, but I’ll stick with the original. To investigate life-in-the-Universe perhaps we should start a bit closer to home and look to our own solar system. Apart from Planet Earth, we have no absolute proof positive to date that any other life, albeit relatively simple forms compared to terrestrial life forms such as ourselves and associated companion animals and plants, exists within the confines of our solar system. However, I conclude in this overall summary the odds are fairly high, almost certain in fact; those other, albeit relatively simple extraterrestrial life forms do exist in our immediate cosmic neighbourhood. 

Life is ultimately nothing more than an ongoing series of complex biochemical reactions. These sort of reactions tend to be optimal at warmer (quasi Earth-like) temperatures. Too cold and the necessary chemical reactions are too sluggish, if they proceed at all. Too hot, complex organic molecules rapidly break down. So, Titan (moon of Saturn) is probably way too chilly even though it has a thick atmosphere and lots of organic molecules on the surface, even organic liquids forming large lakes if not exactly oceans. The surface of Venus in contrast is way too hot, but it has a thick atmosphere that’s a lot more temperate at higher altitudes. Some real estate is both too hot and too cold at the same time – Mercury and Luna (our Moon) for example and lacking any real atmosphere and liquid water aren’t top of the pops for finding life, however simple.

Mars, long associated with intelligent extraterrestrial life, is still a near certainty for much housing far simpler extraterrestrial life forms, like microbes. There are many independent chains of observational evidence that support that conclusion. Proof positive however, still waits.

Europa (moon of Jupiter) has in all probability a liquid water ocean beneath a global ice cap. Water plus a geothermal/tidal energy heat source opens up a good plausibility for going ice fishing to our descendents several generations down the track. There are several other moons with ice cap surfaces covering possible liquid oceans that might rival Europa as an eventual fishing destination.

My favourite solar system locations for (probably) tough-as-nails microbial life, Mars apart, are the upper atmospheres of the Jovian (gas giant) planets (Jupiter and Saturn; maybe Uranus and Neptune). Their atmospheres are rich in organics and no doubt water vapour.  The gas giants, Uranus excepted, radiate more heat energy than they receive from the Sun. There will be regions in their upper atmospheres that have Earth-like temperatures; there will be a lot of atmospheric mixing (useful for bringing different chemicals together); and of course these planets will also have been seeded with organics and water from space via comets, meteors, cosmic dust, etc., if not in fact seeded directly with microbial life forms via the Panspermia hypothesis.

The problem in finding out for sure is going to revolve around sending appropriate instrumentation into those planetary atmospheres that will be able to detect actual life forms, as opposed to just measuring just purely physical parameters and chemical constituents. So, don’t expect definite answers anytime soon.  

Lastly, we can’t rule out comets and meteors from housing dormant extraterrestrial microbial life forms.

Exobiology: Life in the Outer Solar System: The Smaller Bodies

Exobiology was the original term given to the sciences central to the question of life-in-the-Universe. It’s now been largely replaced by Astrobiology, but I’ll stick with the original. To investigate life-in-the-Universe perhaps we should start a bit closer to home and look to our own outer solar system and some of the smaller abodes. Apart from Planet Earth, we have no absolute proof positive to date that any other life, albeit relatively simple forms compared to terrestrial life forms such as ourselves and associated companion animals and plants, exists within the confines of our solar system. However, the odds are fairly high, almost certain in fact; those other, extraterrestrial life forms do exist in our immediate cosmic neighbourhood. 

Europa (A Satellite of Jupiter): Europa is, apart from Mars, the current darling of the exobiology (astrobiology) set. There is evidence that Europa has a liquid water ocean underneath a thick ice cap that is kept from freezing solid by the flexing action imposed on the moon by its parent planet, Jupiter. If you have liquid water, an energy source, you therefore have possible life, or so goes the thinking.  I’m not quite as optimistic. The ice cap is thick enough so that any energy source available for life won’t be solar. The ocean will be in eternal darkness. That is however not a death blow as not all critters on Earth rely on solar energy. There could be hydrothermal vents, with associated living communities on Europa as there is on Earth. But, with the ice cap, there would be little in the way of resources added to the ocean from outside; that’s not the case on Earth. All chemicals that would sustain such life would have to be efficiently recycled. Life on Europa – possible, but it’s going to prove to be very difficult to explore that ocean, so I’m not expecting a definitive answer any time real soon.

However, there remains the possibility that materials contained within that hypothetical ocean may, due to tidal stresses, may be squeezed through cracks in the ice and find their way to rest on the surface. It’s therefore possible that a robotic craft that lands on the icy surface might detect organics and/or fossil or frozen solid microbes or even dead multicellular life forms resting on the surface.

[Note: To avoid unnecessary repeats, as a general rule of thumb, any satellite around Jupiter, Saturn, Uranus or Neptune that has a substantial part of it’s crust made up of ice, and is subject to extreme tidal heating by it’s parent planetary body (i.e. – you get a liquid ocean underneath a thin covering of ice), you have the potential for, as in the case of Europa, a habitable water-rich environment.]

Titan (A Satellite of Saturn): The satellite of Saturn, Titan, is one of the largest moons in the solar system, and in fact, if it existed all by its lonesome, could be considered a planet in its own right. Titan has, fairly unique among satellites, a dense atmosphere. It’s denser in fact than our own atmosphere. It also has the right sorts of chemicals that we identify as having a strong connection with organic and biochemistry. Were Titan the same distance from the Sun that Earth is, well, you could have a real twin of Earth, unlike our false twin, Venus.

Unfortunately, Titan is way, way, way – far away – from the solar energy source that makes Earth such a relative paradise. Thus, Titan is Earth, but an Earth in slow motion because Titan is so cold compared to Earth. If you think of Earth as liquid water at the equator, Titan is molasses at the poles!

Comets, Asteroids/Planetoids, Meteors: These relative tiny bodies can’t really qualify as habitable abodes to life, except, there’s evidence that not only can some of the above be rich in the sorts of chemicals associated with life (water, carbon compounds and organic chemistry), they could indeed be environments that could house dormant life forms or fossil life forms of a unicellular kind. Meteorites which have been gathered up and analysed on Earth (like ALH 84001) have yielded if not fossilised bacteria, then at least enough chemical evidence to suggest that they could have had a close connection with contributions towards an origin of life event.