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Saturn's largest moon Titan is by far the strangest place in the solar system: An unimaginably frigid world with a thick, opaque atmosphere where the clouds rain liquid natural gas, the "rocks" and mountains are composed of water-ice as hard as granite, and rivers of hydrocarbons run to organic chemical seas.  It is a world with eerie similarities to the processes that shape Earth, and yet is so far outside our frame of reference in temperature and bizarre chemistry that even visiting it with robotic probes presents unique technological challenges.  But most importantly, while Titan may someday become a human world, the most fascinating thing of all about the Orange Moon of Mystery is what may already live there.  In Vol. 5, we look at the possibility of Titanian life, and what the future may hold for humankind in this bizarre environment.

The progress of our adventure so far (current in bold):

1.  The Sun
2.  Mercury
3.  Venus
4.  Earth (Vol. 1)
5.  Earth (Vol. 2)
6.  Earth (Vol. 3)
7.  Earth (Vol. 4)
8.  Earth (Vol. 5)
9.  Earth (Vol. 6)
10.  Luna
11.  Mars (Vol. 1)
12.  Mars (Vol. 2)
13.  Mars (Vol. 3)
14.  Phobos & Deimos
15.  Asteroids (Vol. 1)
16.  Asteroids (Vol. 2)
17.  Asteroids (Vol. 3)
18.  Ceres
19.  Jupiter (Vol. 1)
20.  Jupiter (Vol. 2)
21.  Io
22.  Europa (Vol. 1)
23.  Europa (Vol. 2)
24.  Ganymede
25.  Callisto
26.  Saturn (Vol. 1)
27.  Saturn (Vol. 2)
28.  Saturn (Vol. 3)
29.  Rings of Saturn
30.  Mimas
31.  Enceladus
32.  Tethys
33.  Dione
34.  Rhea
35.  Titan (Vol. 1)
36.  Titan (Vol. 2)
37.  Titan (Vol. 3)
38.  Titan (Vol. 4)
39.  Titan (Vol. 5)
40.  Iapetus
41.  Minor Moons of Saturn
42.  Uranus
43.  Miranda
44.  Ariel
45.  Umbriel
46.  Titania
47.  Oberon
48.  Neptune
49.  Triton
50.  The Kuiper Belt & Scattered Disk
51.  Comets
52.  The Interstellar Neighborhood
53.  Updates
54.  Overview: Human Destiny Among the Worlds of Sol
55.  Test Your Knowledge
PIA09833

IV.  Potential Biosphere

In Earth (Vol. 3), we looked at the chemical properties of H2O that make it essential to Life As We Know It (LAWKI):

1.  As a liquid, it dissolves other substances without (generally) changing them, so materials can be "liberated" by water to move around without being robbed of their reactive properties.  This is why it's known as a "universal solvent."

2.  Water becomes less dense as it freezes, so its ice stays on top of liquid to serve as thermal insulation.  This allows it to create a stable temperature range so that certain chemical reactions can occur reliably inside a body of liquid water even if the outside environment is below the freezing point.

2.  Water has a strong surface tension or "stickiness," so it can remain liquid for an extended period of time even if the outside environment is warm enough that it would otherwise tend to evaporate quickly.  This keeps water stable at the other end of the temperature spectrum.

To summarize, liquid water does a number of things to promote the chemistry of LAWKI: Moves the chemicals around to promote interactions; does not itself hinder reactions by changing the chemicals; and keeps temperatures within a certain stable range that promotes ongoing complex chemistry.  Not a lot of substances can do all that: There are a few that can do them under very limited sets of conditions - narrow temperature and pressure ranges that intersect even more narrowly - but the smaller the range, the rarer and less stable they would be, made even rarer based on the relative abundance of the substance itself.

Since H2O is abundant in the universe as a compound, and its liquid phase is the only basis for life we know of so far, science tentatively assumes that water is necessary for life and therefore that biochemistry based on water is the only life in the universe.  This doesn't rule out alternatives or discourage the search for exotic life, but is just the simplest assumption to go by in the absence of specific evidence to the contrary.  So, to date, scientific searches for extraterrestrial life focus on environments where liquid water is known or thought to occur - particularly under the surface of Mars, but with growing focus on Europa and Enceladus.

As we saw in Titan (Vol. 2), it's thought that Titan also has a subsurface liquid water ocean, although the evidence for it is less definitive than for Europa and Enceladus.  However, the surface of Titan is so cold that essentially zero liquid water exists under normal conditions - basically all of the H2O is as solid as it gets, hard as granite.  But given some evidence for cryovolcanism (i.e., tectonic activity that heats areas of the ice crust to liquid temperatures), there is a bit of wiggle room in the "normal conditions" statement.  

Even if it's very rare, any amount of liquid water rising high enough to interact with the complex organic substances of the surface would be extremely reactive.  Titan is a large and dynamic world with a massive abundance of H2O and larger abundances of organic compounds than exist on Earth, so just intuitively it would seem that something resembling familiar chemistry should occur somewhere, sometimes, albeit definitely not on the surface.  That's not scientific evidence, but it would be surprising if it were thoroughly devoid of LAWKI even in hypothetical areas where surface chemicals and subsurface geology interact.

But that's not even the most interesting subject, because water is not the only abundant compound that can serve as a biochemical medium: As it turns out, liquid methane (CH4) can serve the same purposes at much lower temperatures, although the results would be somewhat exotic.  For instance, it's not as conducive to free interaction among dissolved chemicals as water is, but at the same time is less destructive to complex molecules that do form, so in some ways its advantages and disadvantages balance out.  This means it would statistically take longer for any given interaction to occur, but the chemicals would survive longer and thus have extended opportunities to reach each other.

Titanian life is not entirely speculative at this point: Predictions about the chemical behavior of Titan's atmosphere in the presence of methane-based life have proven consistent with actual observations by the Cassini spacecraft - namely, an anomalously low abundance of acetylene and a net flow of hydrogen toward the surface.  Life is not the only possible explanation for the results, but the fact that observations are deviating so markedly from non-biological expectations while following biological predictions is generating excitement.  Still, scientists don't consider it to be concrete evidence as yet.

Methane-based life (not to be confused with known methane-breathing life, which is still water-based) would probably metabolize and evolve very slowly because of the properties of methane, so if it exists, it would likely be simple (though simple doesn't necessitate "small," so don't let that cramp your imagination).  Evolution is based on an accumulation of large numbers of chemical events, so the fewer the number of events, the less "biological time" is able to pass relative to any given fixed timescale.

Going purely speculative, we can imagine methane-based lifeforms that (very slowly) consume water as a solid mineral and utilize limited quantities of it internally to aid cellular processes.  Physically, it's easiest to imagine some sort of life developing in the shallow river deltas and fjords, because that's where there would be the most mutual interaction between the liquid, the solid water surface, and the atmosphere.  That's also the kind of environment where the greatest profusion of life exists on Earth, for the same reasons.  You'd want to look in places like this:

Kraken Mare

PIA09180

Animal life is unlikely due to the very low energy of the environment, but sessile (i.e., non-moving) life that absorbs from its environment is more plausible.  If I were to write science fiction based on the idea, I could imagine a few conceptual lifeforms: Fragile little "bubbles" that are just thin membranes intersecting each other and attached to the surface; tenuous filaments that form tiny nets; etc.  Think "delicate."  But whatever it might look like under a microscope or up close, if it exists we will probably know about it first through the kind of atmospheric studies that have already provided tantalizing clues.

In other words, we will "smell" ET life long before we ever see it, and the same is probably true even of ET intelligence as well - i.e., we would detect the chemical byproducts of artificial technology in the atmosphere of some distant exoplanet some day.  But long before that happens, we will almost certainly detect - and may already have detected - the signature of simpler life in the atmospheres of other worlds, possibly even in our own solar system.  We've already seen anomalous observations in the atmosphere of Mars that would be conducive to LAWKI (though far from proving its presence), and the Cassini data may yet prove to be the first clues of exotic life on Titan.  In the meantime, enjoy this fun little chemistry demonstration illustrating some properties of liquid methane:

Liquid CH4 is clear in pure form, but on Titan it would be brown or black due to all the other organic chemicals suspended in it.  It might be clear as rain though.

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V.  Modern Relevance to Humanity

Titan today means several different things to humanity: One as a symbol of mystery in literature and fiction; another as a setting for actual exploration in science fiction; and a third as a real world being pursued with real technology.  As a symbol of mystery, Titan is the MacGuffin for the main character's elaborate fraud in the 1997 film Gattaca: A man born underprivileged due to lack of genetic engineering wants to be an astronaut and explore Titan, so the film tracks his progress advancing through the corporation (Gattaca) that selects and trains astronauts while masking his true biological identity.  Gattaca is also one of the most inspiring and beautiful films ever made, that captures the spirit of the underdog without in any way cheapening it.  It was something of a spiritual anthem for me as a young adult (I still can't hear the theme song without feeling something), but it's relevant mostly for its vague and rare references to Titan as the main character's destination (which they never show).  Clips:

There have been a couple of more recent depictions of Titan that are more specific, although they're both just environmental rather than really exploring anything about it.  In an episode of the comedy-scifi TV show Eureka, the town's humanoid android sheriff is accidentally transported to the surface of Titan and his nuclear power sources slowly wind down in the ultra-cold.  Eureka was never a serious science fiction show, but it was among the very first to even bring Titan to the attention of audiences and give a vague rendition of its surface conditions:

Eureka Titan Episode

Then there was the 2009 Star Trek reboot's brief, inaccurate scene where the Enterprise emerges from the clouds of Titan.  First of all, it isn't clouds that obscure Titan, it's haze, so you don't suddenly pop up out of haze the way you would out of a cumulus cloud deck - you just kind of fade in as you get closer to the viewer's perspective.  So if Enterprise were emerging from Titan, it would be visible as a hazy blur some distance away like an airplane in a smoggy sky, then it would just gradually resolve as it approached.  There would be no "surfacing whale" effect as shown in this scene, so this is just Hollywood hokum with no connection to reality - especially as it shows Saturn, which they should have really known better by now:

The most realistic depiction I've ever seen of Titan in fiction was actually in a 1997 novel by Stephen Baxter bluntly called Titan: Baxter's brand of science fiction is mordantly masochistic, so he revels in showing how miserable space is and can be, the vast numbers of ways to die, the incredible hostility of other environments, so this book is not inspirational by any stretch of the imagination.  But I would read it for a relatively realistic look at the negative side of a human undertaking to Titan, albeit coupled with unfettered (and IMHO unecessarily caustic) apocalypticism on Earth.

Baxter Titan

Before the Cassini-Huygens mission arrived in the Saturn system in 2004, scientists were primarily focus on Mars and to a lesser extent Europa in searching for life on other worlds, but this mission has actually yielded two new subjects - Titan and Enceladus, with Titan being the most overwhelmingly exotic world yet encountered.  The focus of exploration programs remains on Mars largely because it's a lot closer, a lot easier to reach, and its environment is much easier to deal with than anything in the outer solar system, but if all else were equal, Titan would definitely steal the limelight.  If Mars and Titan were to switch places in the solar system, no one would care about Mars at all - it would be just another dead rock out in the wastelands.  But because Titan is so exotic, it's still highly attractive despite being way out there and requiring years of transit time.

Its greatest practical use to science today is as a large-scale climate laboratory to better understand how our own world's atmosphere is evolving, the effects of various chemicals on climate, and the complex patterns that can develop as a result.  We're nowhere near having even the rudimentary beginnings of an understanding about Titanian climatology - as I've said before, all we know comes from a handful of infrequent flybys by Cassini - so we will need to send dedicated climate orbiters and hopefully, some day, weather balloons and rovers to figure out that level of detail.

Toward that end, hopefully efforts are being made to simulate the Titanian environment on Earth for the development and testing of exploration equipment on a substantial scale.  The facilities already exist for small-scale simulations to test how small amounts of substances behave in various conditions, but there are probably not the kind of large test chambers that would be used to test large-scale operational technology.  Not yet, anyway, so it may be a while before Titanian robotic exploration ramps up the way it's been ramping up on Mars lately.

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VI.  Future Relevance to Humanity

Once landing on Titan, leaving again would be a big technological headache.  Centuries of experience running rockets in vacuum, from Mars, or from Earth isn't going to help knowing how to build rockets that could safely and effectively take off through high-pressure cryogenic chemical hazes and cloud systems.  There would have to be decades of trial-and-error through robotic exploration sample return missions, tangent flights that fall just into the atmosphere and then ignite their engines to leave again, and other experimental efforts before they'd really know what they're doing enough to attempt human transportation.  A civilization that had centuries of experience operating in vacuum environments still wouldn't immediately know how to build rockets that could take off and operate through high-pressure cryogenic clouds and hazes, so Titan would be a challenging frontier even for people who easily hop around among asteroids, other gas giant moons, and the terrestrial planets.

Cloud cities are one remarkable possibility for world like Titan: Low gravity, high pressure, high air column means that derigible facilities could be workable.  The main limitations are that the higher you are, the less atmospheric protection received from Saturn's radiation belts, but the lower you are, the more you interact with the complex cryogenic clouds that impose all sorts of thermal regulating requirements on your bulkhead materials.

You might think an atmosphere and seas full of natural gas would be an energy-rich environment, but that's not really the case: We can use methane as a fuel on Earth because our environment already contributes a lot of heat to the combustion process, and provides the oxygen that makes it possible.  On Titan oxygen is bound up in surface solids, so you have to invest energy to get it out of the ice before you could even begin to use the atmosphere combustibly.  And once you did, the energy you got back from introducing the oxygen to the atmosphere would be less than what you put in to get it from the ice.  We really have a free ride here on Earth thanks to the Sun and millions of years of its energy stored in high-temperature fossil fuels.  

Moreover, while Titan has strong winds, a windmill probably wouldn't be able to harvest enough energy to keep itself from breaking down in the extreme cold, and (as far as we know) there are no locally-available materials with which to maintain it - unless you used plastics, but turning hydrocarbons into plastics takes energy, so you're still stuck.  In other words, the only viable energy sources on Titan are nuclear in nature, and the only sustainable ones remain to be developed - namely, fusion or antimatter harvesting.

There will not be views of Saturn or other moons thereof from the surface except in non-visible spectra that the atmosphere is transparent to, especially when the lights of human installations are lighting up the clouds and hazes from beneath, so one might expect people who live there to prefer having their views of the outside in infrared or other wavelengths.  Advanced forms of polarized windows might provide these views, and perhaps also advanced spacesuit visors - once technology has advanced to the point that a spacesuit could handle the thermal demands of Titan.  It's nowhere near that point now, and really you'd basically need some kind of miniaturized nuclear reactor in each suit, and its thermal properties would have to be so carefully designed that it doesn't allow its heat to conduct into the surface (remember, you're walking on water ice and hydrocarbon solids - potentially explosive mixtures if the temperature gets too high, not to mention maybe turning into quick-sand or mud before it even got that far).

Same thermal challenges apply to the habitat infrastructure, so it would have to be thermally isolated from the surface.  But even then there are going to be extreme long-term problems with living on Titan, because there's no way to safely get rid of the waste heat of civilization under such conditions: On an icy moon with no atmosphere like Ganymede, you could just build radiator towers to radiate the heat into space instead of melting the ground beneath your feet.  But if you do that on Titan, the energy isn't leaving - it's just going into the atmosphere where it's being stored at hyper-efficiency because of all the methane.  

The anti-greenhouse effect mentioned earlier is only occurring because the energy coming in from outside is being blocked, but energy generated on the surface would be conserved with high efficiency.  So (a)you'll have to be very careful to spread out the radiation of waste heat so that it doesn't create concentrated high-temperature areas around the radiators that could explode if the wrong chemistries happen to build up nearby, and (b)over time, terraforming would be unavoidable just by being there, so colonists would have to make coordinated efforts to control and balance the process of change so it doesn't spiral out of control and destabilize the ice surface while making the atmosphere unsurvivably turbulent.

Transition points in any Titan terraformation scenario would be tricky and turbulent.  You would first have to radically reduce the amount of methane in the air and change the chemistry of the surface before adding oxygen or messing with the temperature, because if at any point you add oxygen or raise temperatures significantly to introduce water-vapor pressure while it's still hydrocarbon-rich, you would cause regional or global "ignition events" where the atmosphere and surface would burn.  It's unlikely that humans could continue to exist anywhere in the Titanian environment, surface or atmosphere, while such things were happening, and it could take quite a while before things would settle down enough for that to change.  What came out it probably would not be helpful either - an extremely turbulent, shattered, unstable surface, and an environment where the methane seas and lakes are gone.

In other words, there are really only two choices as far as human colonization of Titan is concerned: Either destroy everything that makes it unique and turn it into something we like more, or don't settle there at all.  As long as there are no complex living organisms already there - which is highly unlikely given the slowness of evolution that would occur even if there were a biosphere - both options are ethically legitimate.  No matter how beautiful and exotic a place is, that has to take a back seat to the imperatives of life.  To both live on Titan and preserve it would require heat-expulsion technologies that don't presently exist, that would allow people to send the waste heat of civilization past the atmosphere and into space where it wouldn't change anything.  How that could be accomplished is hard to imagine within the laws of thermodynamics.

Given human nature, it's easy to imagine people settling Titan and then just procrastinating about the long-term realities until it's too late.  It's easy to imagine their being in denial, and dismissing both radical terraformers who say they have to deliberately destroy the character of Titan or else they'll destroy it anyway in an uncontrolled process, and the folks who say they have to leave altogether and just let it continue naturally as some kind of nature park rather than a setting of human nations.  

And so it's easy to imagine human civilization on Titan being temporary, and self-destructing when it inflicts uncontrolled terraforming on its environment that makes it impractical to continue living there: Sink-holes and cracks kilometers-wide opening up in the ice crust, the surface falling apart into itself as thermal changes inflict tectonic consequences, both small and large ignition events signaling the changing chemistry, winds reaching unsurvivable speeds that make travel impossible and further deform the surface, etc.  If that happened, the very different world that came out of such a process would not much resemble its past, and the remains of human cities would be buried under kilometers of ice-rubble or sand-blasted into oblivion by the winds: Pompeii on a world-scale.

The other alternatives, as mentioned, are controlled terraformation - which would involve some political consensus to deliberately destroy the environment generations of people had identified as their home (which doesn't seem very likely), or else keeping Titan off-limits to settlement as a nature park that people from other places in the Saturn system or even the rest of the solar system could visit and explore under strict regulation (which also seems dubiously far-sighted for humans).  

VII.  Future of Titan

Either we maul Titan and turn it into something more conducive to human survival, or we leave it alone as kind of a theme park, or we abandon it altgether to evolve as it will.  If the former, it would eventually join the exotic other human-space worlds growing toward becoming whaver uminaginable webs of civilizations they do.  He theme park possibility offers a number of unusual possibilities - use your imagination. That last and easier possibility leaves Titan to develop naturally in which case it wuld be the case until the Sun expand and heats Titan until it's warming up to support some forms of LAWKI life a few billion years from now under a reg giang while the earth is a burnt cirsper inside the Sun

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VIII.  Catalog of Exploration

1. Past and Current Proves:

Voyager 1 (USA - 1980 flyby)
Voyager 2 (USA - 1981 flyby)
Cassini (USA and Europe - entered Saturn orbit 2004, currently operating)

2.  Future Operations:

(none finalized)

Welcome to your new home, if you want it - I promise an endless series of wonders and surprises:

titan_25km (processed and rendered)

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