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Questions popping up in my mind: 1) Why are organic materials (probably any carbohydrates) only supposed to come from the surface? Would it not be plausible to

by generic92034 3y ago

Questions popping up in my mind: 1) Why are organic materials (probably any carbohydrates) only supposed to come from the surface? Would it not be plausible to assume that Titan's ocean ground contains significant amounts of carbon? 2) Why do they assume that there are only dilution processes in an ocean (surface or subsurface). There could be currents and suboceanic terrain features concentrating carbon-rich water (at least I do not know any reason against this).

RIMR 3y ago
These are great points. It would be like if a race of flying / buoyant aliens studied Earth's upper atmosphere, and decided that it wasn't sufficient for life, while ignoring that life isn't really found until you get to the surface, and most of that life is found under the surface. There could be a habitable zone deep in Titan's oceans. I don't even know if "habitable" is the right word, because the concern seems greater to do with the genesis of life, not the sustainability of existing life that might have existed on Titan for millions of years already, from a time where perhaps conditions were very different from what they are today.
- margalabargala 3y ago
  To be fair, the scientists that wrote the scientific article came to no such conclusion. The "most likely uninhabitable" thing is an invention of the popsci journalist whose article was linked, not something supported by the underlying journal article. The journal article asked the question "is the carbon transferred from Titan's surface to its ocean sufficient, on its own, to sustain a biosphere?" to which their answer is "probably not". It explicitly does not claim there are no other sources of carbon in the ocean, nor that Titan is "probably uninhabitable".
margalabargala 3y ago
The actual study this article is about is addressing a very specific question. The article posted takes that specific conclusion and applies it more generally, especially when writing the headline. Titan has a methane atmosphere, due to prior outgassing from its surface. Methane is destroyed by sunlight; i.e. over time, the atmosphere is reacting with itself and sunlight to form more complex carbon molecules, which fall out of the atmosphere onto the surface. The study does not look at the carbon content of the ocean itself, it simply evaluates whether these complex carbon molecules, that we know are forming in Titan's atmosphere through well-understood processes, can also mix with the liquid ocean. As the ice sheet covering the ocean is at minimum 40km thick, and over 100km thick in places, it is difficult for surface molecules to penetrate. Whether or not other carbon sources, such as from within the planet, contribute carbon to Titan's oceans are beyond the scope of this study, and will remain beyond the scope of our knowledge until we manage to place equipment on Titan capable of drilling through tens of kilometers of ice. The actual paper concludes that carbon transfer from the surface to the ocean is not sufficient to support a biosphere if that is the sole source of carbon. It specifically calls out "unless biologically available compounds can be sourced from Titan’s interior" as something that would allow a biosphere. EDIT: link to article full text: https://www.researchgate.net/publication/377929149_Organic_Input_to_Titan%27s_Subsurface_Ocean_Through_Impact_Cratering https://www.researchgate.net/publication/377929149_Organic_I...
- generic92034 3y ago
  Ah, I see. My bad for not drilling deeper and reading the underlying study. In my eyes neglecting the inner planet as source of carbon (only referring to the article here) is a rather large gap. I am all for shooting some equipment up to Titan. Although I am not sure we have the technology and the will to commit resources to analyze Titan's oceans in detail, yet.
  - margalabargala 3y ago
    No worries. I think it's reasonable to expect that people who write articles about journal articles would do a good job describing their conclusions. The whole point is that reading the underlying study shouldn't be necessary. I think this was an important study to be done, because if the conclusion came out the other way, that would have been very exciting. We would then be able to say "using only the aspects of Titan we know for certain to be true, we can model a plausible sustainable biosphere". A positive result would have been very promising, but this negative result should not be seen as discouraging.
- floxy 3y ago
  Anyone know the pressure at the top of Titan's ocean? (That is, just under the ice) At first blush I was thinking it might be pretty substantial for a submersible with that much ice, but then the gravity is significantly less than earth (0.138*g). Using: Pressure = density * g * h ...with density of water as 997 kg/m^3, g = 0.138 * 9.8 m/s^2, and h = 40000 m, you get a pressure of ~540 atmospheres. But I don't know if the ice sheet would have a structural component that doesn't add as much as a naive calculation would suggest.
thaumasiotes 3y ago
> Why do they assume that there are only dilution processes in an ocean (surface or subsurface). Presumably for the same reason that mine operators assume that all minerals are evenly distributed throughout the earth's crust.

RIMR 3y ago

These are great points. It would be like if a race of flying / buoyant aliens studied Earth's upper atmosphere, and decided that it wasn't sufficient for life, while ignoring that life isn't really found until you get to the surface, and most of that life is found under the surface. There could be a habitable zone deep in Titan's oceans. I don't even know if "habitable" is the right word, because the concern seems greater to do with the genesis of life, not the sustainability of existing life that might have existed on Titan for millions of years already, from a time where perhaps conditions were very different from what they are today.

margalabargala 3y ago
To be fair, the scientists that wrote the scientific article came to no such conclusion. The "most likely uninhabitable" thing is an invention of the popsci journalist whose article was linked, not something supported by the underlying journal article. The journal article asked the question "is the carbon transferred from Titan's surface to its ocean sufficient, on its own, to sustain a biosphere?" to which their answer is "probably not". It explicitly does not claim there are no other sources of carbon in the ocean, nor that Titan is "probably uninhabitable".

margalabargala 3y ago

The actual study this article is about is addressing a very specific question. The article posted takes that specific conclusion and applies it more generally, especially when writing the headline. Titan has a methane atmosphere, due to prior outgassing from its surface. Methane is destroyed by sunlight; i.e. over time, the atmosphere is reacting with itself and sunlight to form more complex carbon molecules, which fall out of the atmosphere onto the surface. The study does not look at the carbon content of the ocean itself, it simply evaluates whether these complex carbon molecules, that we know are forming in Titan's atmosphere through well-understood processes, can also mix with the liquid ocean. As the ice sheet covering the ocean is at minimum 40km thick, and over 100km thick in places, it is difficult for surface molecules to penetrate. Whether or not other carbon sources, such as from within the planet, contribute carbon to Titan's oceans are beyond the scope of this study, and will remain beyond the scope of our knowledge until we manage to place equipment on Titan capable of drilling through tens of kilometers of ice. The actual paper concludes that carbon transfer from the surface to the ocean is not sufficient to support a biosphere if that is the sole source of carbon. It specifically calls out "unless biologically available compounds can be sourced from Titan’s interior" as something that would allow a biosphere. EDIT: link to article full text: https://www.researchgate.net/publication/377929149_Organic_Input_to_Titan%27s_Subsurface_Ocean_Through_Impact_Cratering https://www.researchgate.net/publication/377929149_Organic_I...

generic92034 3y ago
Ah, I see. My bad for not drilling deeper and reading the underlying study. In my eyes neglecting the inner planet as source of carbon (only referring to the article here) is a rather large gap. I am all for shooting some equipment up to Titan. Although I am not sure we have the technology and the will to commit resources to analyze Titan's oceans in detail, yet.
- margalabargala 3y ago
  No worries. I think it's reasonable to expect that people who write articles about journal articles would do a good job describing their conclusions. The whole point is that reading the underlying study shouldn't be necessary. I think this was an important study to be done, because if the conclusion came out the other way, that would have been very exciting. We would then be able to say "using only the aspects of Titan we know for certain to be true, we can model a plausible sustainable biosphere". A positive result would have been very promising, but this negative result should not be seen as discouraging.
floxy 3y ago
Anyone know the pressure at the top of Titan's ocean? (That is, just under the ice) At first blush I was thinking it might be pretty substantial for a submersible with that much ice, but then the gravity is significantly less than earth (0.138*g). Using: Pressure = density * g * h ...with density of water as 997 kg/m^3, g = 0.138 * 9.8 m/s^2, and h = 40000 m, you get a pressure of ~540 atmospheres. But I don't know if the ice sheet would have a structural component that doesn't add as much as a naive calculation would suggest.

thaumasiotes 3y ago

> Why do they assume that there are only dilution processes in an ocean (surface or subsurface). Presumably for the same reason that mine operators assume that all minerals are evenly distributed throughout the earth's crust.