Life & Temperatures on Titan

[AlexanderHowl]

A possible issue with Titan's water mantle is that it is probably deeper than 75 km. With a density of 1.88 grams per cubic centimeters, it could easily have a water 900 km thick beneath a 100 km thick crust. Of course, there could also be multicellular lifeforms in the water mantle, there are all of the requirements of life, and they might get large enough to pose a threat to a small submersible.

[DataPacRat]

Originally Posted by AlexanderHowl

A possible issue with Titan's water mantle is that it is probably deeper than 75 km. With a density of 1.88 grams per cubic centimeters, it could easily have a water 900 km thick beneath a 100 km thick crust.

I've found a few more papers on Titan's structure, and the most up-to-date data I can find suggests that Titan's outer crust has an overall density somewhere in the range of 0.92-1.65; the ocean 1.30 to 1.35; the high-pressure ice mantle 1.3 to 1.4; and the core 3.395 to 4.490. (And I've got other figures on temperatures, pressures, layer thicknesses, the most likely solutes of the ocean, etc.) The least steady figure I can find is the thickness of the ocean - depending on the source, it's 5-110 km, 75 km, >180 km, or 400 km from top to bottom. (And ever-so-slowly shrinking, as the core loses heat and the icy layers gradually thicken.)

Of course, there could also be multicellular lifeforms in the water mantle, there are all of the requirements of life, and they might get large enough to pose a threat to a small submersible.

As best as I can tell, one important requirement for life is missing in Titan's ocean: an energy source. There's no sunlight; the icy mantle prevents contact between the ocean and the rocky core and also prevents any hydrothermal vents; the temperature gradient is too gradual to be drawn on; there's nowhere near enough radioactives for radiosynthesis; and there aren't enough of the more interesting chemicals to feed on, even the non-Earthly-life reactions like combining hydrogen with acetylene (both of which can at least be found in Titan's atmosphere, if in minute quantities).

About the only real option I've come up with is if some Earthlings dropped some reactors into the ocean, along with some life custom-tailored both for the environment and to draw on whatever form of energy the reactors were designed to emit. ... Or, depending on how broadly you want to describe 'life', someone might have launched some giantish TL10ish flexibody eel-bots.

[AlexanderHowl]

The liquid water mantle cannot have a density above 1, as water cannot be compressed. From what I have read, the current research on Titan suggests that 50% of its mass is in rocky material while 50% of its mass is in volatile materials. Since Titan possesses expansion fractures rather than compression fractures, it is constantly renewing its surface through cryovolcanism rather than shrinking.

A possible structure is an icy volatile crust over a carbon rich slurry over a liquid water mantle over a rocky core. The kinetic energy during its rapid formation (probably over 30,000 years) would have generated massive amounts of heat that became trapped by icy volatile crust (similar to the most recent research on the formation of Pluto). Precipitation of ice, radioactive decay from the rocky core, and tidal energy from its moderately eccentric orbit around Saturn would have maintained the total heat in the system, resulting in a rich place for a strange life.

The warm water mantle creates plumes of liquid water the rise up through the carbon slurry and melts through the icy crust. Where the water does not quite come to the surface, the added heat allows for carbon slurry geysers. When the water reaches the surface, it creates water volcanoes that replenish the surface ice. Since Titan has a young surface similar to the Earth's, it probably possesses equivalent levels of volcanic activity.

A rocky core with a density of 5.6 grams per cubic centimeter and a radius of 1500 km would produce enough thermal energy through radioactive decay to maintain the liquidity and warmth of a 800-900 km thick water mantle for billions of years, with the added energy from precipitation and tidal flexing. While a moon like Titan could have a less dense larger core, it becomes much harder for Titan to maintain a liquid core without unusual amounts of radioactive decay. A thicker water mantle also allows for more insulation, which would retain the heat from the initial formation longer, requiring only normal amounts of radioactive decay.

[DataPacRat]

May I just pause a moment to mention how pleased I am to be able to have this sort of discussion on this forum? ... Okay, I'm good. :)

Originally Posted by AlexanderHowl

The liquid water mantle cannot have a density above 1, as water cannot be compressed.

For pure water, that's true; but the reports I've been reading have suggested that Titan's liquid-water mantle is extremely salty, with the pop-sci articles referring to it as salty as "the saltiest seas on Earth", and mentioning the Dead Sea and its 40% salinity.

(Various reports have mentioned that the solutes likely include Cl -, HCO3 - (bicarbonate), and SO4 2- (sulphate); and Na +, Ca 2+, Mg 2+, K +, and NH4 2+ (ammonium). At the moment, I'm positing that at least one borehole was dug down to the subsurface ocean to un-dissolve some of those inorganic minerals for local industrial use.)

From what I have read

About all I can mention is what I've been reading myself, lately; here's the most relevant items from my browser's recent history:

https://elib.dlr.de/90334/1/2014-soh...jgre201246.pdf
https://cyber.sci-hub.tw/MTAuMTAxNi9...baland2014.pdf
https://zero.sci-hub.tw/1357/1dad0cc...fortes2012.pdf
https://www.lpi.usra.edu/meetings/lpsc2012/pdf/2939.pdf
https://www.hou.usra.edu/meetings/lpsc2014/pdf/2435.pdf
http://www2.ess.ucla.edu/~jewitt/cla...rs/Wood_10.pdf
https://agupubs.onlinelibrary.wiley....9/2010GL044398

, the current research on Titan suggests that 50% of its mass is in rocky material while 50% of its mass is in volatile materials. Since Titan possesses expansion fractures rather than compression fractures, it is constantly renewing its surface through cryovolcanism rather than shrinking.

I spent last evening mostly focusing on Titan's subsurface ocean; looks like tonight, I'll be expanding my search parameters to cryovolcanoes and stress fractures.

A possible structure is an icy volatile crust over a carbon rich slurry over a liquid water mantle over a rocky core.

Might I ask where you found that proposal? Pretty much every paper I've found suggests layers of icy crust, liquid water, high-pressure ice, and rocky core. (With most of the disagreements being on the layers' thicknesses, and various details about the core.)

The kinetic energy during its rapid formation (probably over 30,000 years) would have generated massive amounts of heat that became trapped by icy volatile crust (similar to the most recent research on the formation of Pluto). Precipitation of ice, radioactive decay from the rocky core, and tidal energy from its moderately eccentric orbit around Saturn would have maintained the total heat in the system, resulting in a rich place for a strange life.

The warm water mantle creates plumes of liquid water the rise up through the carbon slurry and melts through the icy crust. Where the water does not quite come to the surface, the added heat allows for carbon slurry geysers. When the water reaches the surface, it creates water volcanoes that replenish the surface ice. Since Titan has a young surface similar to the Earth's, it probably possesses equivalent levels of volcanic activity.

A rocky core with a density of 5.6 grams per cubic centimeter and a radius of 1500 km would produce enough thermal energy through radioactive decay to maintain the liquidity and warmth of a 800-900 km thick water mantle for billions of years, with the added energy from precipitation and tidal flexing. While a moon like Titan could have a less dense larger core, it becomes much harder for Titan to maintain a liquid core without unusual amounts of radioactive decay. A thicker water mantle also allows for more insulation, which would retain the heat from the initial formation longer, requiring only normal amounts of radioactive decay.

Any suggestions on how common the geysers and volcanoes would be? I'm wondering how consistent any of the underlying warm-water plumes would be; for instance, to figure out how often any particular settlement might be threatened by some new geology, and/or how often some active interventions down in the ocean might be needed to nudge a plume towards a less disruptive exit point.

[Anthony]

Originally Posted by AlexanderHowl

The liquid water mantle cannot have a density above 1, as water cannot be compressed.

Untrue; it's not very compressible (looks like about 4% at 1,000 atmospheres) and at a certain point it just turns solid, but it's not entirely incompressible.

[AlexanderHowl]

The maximum compressability of water is around 2% (so that is the maximum density increase that water would experience), though it does become solid around 1 gigapascal, depending on salinity and temperature. At a depth of 1,000 km of Titan, the pressure would be around 1.6 gigapascal (assuming 10% salinity), so it could remain liquid at a temperature of 20 C. Of course, if Titan possesses a small iron core, the temperatures could easily reach up to 400 K due to radioactive decay, meaning that any life at the depths would be quite different than Earth life.

[Anthony]

Originally Posted by AlexanderHowl

The maximum compressability of water is around 2%

Figure I found was 4.4-5.1e-10/Pa, or 2% at 40-45 MPa.

[DataPacRat]

Current musings: how much to draw on from 3e Vehicles to add options to 4e UltraTech's sonar-comms, to complicate whatever comm network exists in the subsurface ocean. Eg, VX1 suggests tight-beam and (very) sensitive, which could let somebody reach the 5,000 miles to talk halfway around the planet. (With a bit of delay, given sound's ~1.5 km/s speed in saltwater.) Or could make it easier/cheaper for someone at the top of the ocean chat with someone at the bottom.

(VLF radio doesn't seem to penetrate deeply enough, ELF needs miles-long antennas and has terrible bandwidth, and THS Under Pressure's notes on water transparency put the kibosh on lasercomms of more than half a mile or so. And I'm not using the sort of superscience that permits neutrino comms.)

VX1 also has some numbers for sonar GPS beacons and receivers, though neglects to mention their useful range, or how many should be planted in any given area.

I suspect one of the less-expectedly important factors is how much slower the sonarcomms are than radio, especially for AIs running at faster than realtime...

[AlexanderHowl]

Originally Posted by Anthony

Figure I found was 4.4-5.1e-10/Pa, or 2% at 40-45 MPa.

It decreases with overall pressure and increases with overall temperature. For example, Ice VI (which is one of the extreme pressure ices) is the densest that water becomes at 1.31 g/cm3.

[Anthony]

Originally Posted by AlexanderHowl

It decreases with overall pressure and increases with overall temperature. For example, Ice VI (which is one of the extreme pressure ices) is the densest that water becomes at 1.31 g/cm3.

Which is 24% compression, not 2%.