[HN Gopher] Saturn's largest moon most likely uninhabitable
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Saturn's largest moon most likely uninhabitable
Author : wglb
Score : 56 points
Date : 2024-02-20 19:27 UTC (3 hours ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| renewiltord wrote:
| I see. The reason for this is that insufficient surface organic
| materials make it into the liquid water and the only kind of life
| we know requires those two to combine. Unlucky, I suppose. Would
| have been pretty cool!
| generic92034 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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_I...
| generic92034 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| pavlov wrote:
| _> ' "One elephant per year of glycine into an ocean 12 times the
| volume of Earth's oceans is not sufficient to sustain life," said
| Neish. "In the past, people often assumed that water equals life,
| but they neglected the fact that life needs other elements, in
| particular carbon."'_
|
| Titan's underground ocean is 12x larger than the Earth's oceans?
| I had no idea. Wow.
|
| If this result holds, it's a shame because the gas giant moons
| always seemed like the only chance of discovering some
| interesting extraterrestrial life within my lifetime (or the next
| few dozen generations -- the stars are incomprehensibly distant
| and nearly impossible to visit).
| NoMoreNicksLeft wrote:
| Can't we send two elephants per year? Do they even have to be
| elephants, or can we send plain glycine?
| travisporter wrote:
| Props to Neish - negative results would jeopardize the nasa
| dragonfly mission (co-PI) but still got it published
| RIMR wrote:
| I don't disagree with the assumptions made here, but the
| conclusion is bad. Titan is likely unihabitable for life _as we
| know it_. There are plenty of extremophiles here on Earth that
| live in places we wouldn 't expect life to exist, but we know
| that they can because we found them.
|
| If we make conclusions that we cannot find life on Titan, then we
| never will because we won't be looking. Life could be thriving on
| Titan, but we won't know unless we look for ourselves.
|
| Also, for all we know, Titan's oceans are loaded with organic
| compounds that are don't originate from the surface. We don't
| know what the actual internal structure of Titan looks like
| because we lack the data.
| mbauman wrote:
| Yeah, that's not at all what the actual journal article
| claimed. It starts super simple:
|
| We know Titan has two things that seem so promising for life as
| we know it! Organic compounds on the outside, liquid water on
| the inside.
|
| And then it asks:
|
| Might those two promising things meet? Other work hasn't found
| the tectonics that would do it; could cratering do it?
|
| And that very particular answer is pretty definitively no.
| thriftwy wrote:
| Titan is likely habitable for life as we know it. It's hard to
| imagine why Titan won't have life around hydrothermal vents and
| the like.
| andrewstuart wrote:
| Is there anyone on Earth who thinks it might have been habitable,
| at -292 degrees Fahrenheit (-180 degrees Celsius).
|
| Its weird that there's any narrative at all around this.
| dang wrote:
| " _Please don 't post shallow dismissals, especially of other
| people's work. A good critical comment teaches us something._"
|
| https://news.ycombinator.com/newsguidelines.html
| StanislavPetrov wrote:
| There is a massive ocean of liquid water, which indicates that
| it is substantially warmer than that.
| margalabargala wrote:
| There's a theory that life on Earth began at extremely cold
| temperatures, yes; below -100F.
|
| https://www.discovermagazine.com/planet-earth/did-life-evolv...
|
| It's only Titan's surface that is at -292F, anyway, The theory
| is that life, if it exists, would be present in the subsurface
| ocean, which would be significantly warmer.
| dougmwne wrote:
| This doesn't seem to be a very meaningful theory to draw
| conclusions about life. We have no idea how much carbon is
| already present in Titan's ocean and if there's need for a water
| cycle that connects to the surface. Also this study only
| considers impact craters, not surface tectonics. And there could
| be plenty of carbon sources from ocean floor interactions.
| margalabargala wrote:
| The journal authors agree with you. The "most likely
| uninhabitable" conclusion is an invention of the popsci
| article's author.
|
| The actual article's conclusion is basically "for there to be
| life on Titan, there needs to be more carbon in the ocean than
| would be transferred solely by surface impactors". It
| absolutely does not rule out the existence of those carbon
| source.
| thereddaikon wrote:
| As usual, the reporting on science ends up distorting or even
| inventing conclusions out of thin air.
| margalabargala wrote:
| To quote the two concluding sentences of the journal
| article:
|
| > It is unlikely that the calculated fluxes are sufficient
| to maintain a detectable biosphere, unless the thickness of
| organics on Titan's surface is greater than currently
| estimated, abundant biomolecules are available from Titan's
| rocky core, or surface biomolecules can be delivered to the
| ocean by a process other than impact. Our calculations
| suggest that despite Titan being the most organic-rich
| ocean world in the Solar System, this does not
| automatically imply an organic-rich and habitable ocean.
| JoeAltmaier wrote:
| Perhaps a historical impact could have been large enough to seed
| the ocean.
| andrewflnr wrote:
| The abstract of the actual paper only claims:
|
| > Unless biologically available compounds can be sourced from
| Titan's interior, or be delivered from the surface by other
| mechanisms, our calculations suggest that even the most organic-
| rich ocean world in the Solar System may not be able to support a
| large biosphere.
|
| Which is much less sensationalist, to put it politely.
| arp242 wrote:
| Which is just a different way of saying "uninhabitable".
|
| The middle of the Sahara is uninhabitable. Unless you introduce
| sufficient water and plants that is.
| andrewflnr wrote:
| It is not "just a different way". There's no reason to assume
| impact melting from the surface is the only source of carbon
| in Titan's ocean. The authors of the study seem clear on
| this. I don't know why you feel the need to stand up for
| phys.org on this, or why you think the Sahara is relevant.
| pvaldes wrote:
| > One elephant per year of glycine into an ocean 12 times the
| volume of Earth's oceans is not sufficient to sustain life".
|
| This reasoning is too limited IMAO. Titan oceans may not have
| whales, but for sure could still afford a lot of animals.
|
| 1) It seems that Titan has been there since the early phases of
| solar system creation, so I'll assume that is older than 3
| billions of years (to pick a conservative value). One elephant a
| year for 3 billions of years is still a lot.
|
| 2) Titan could have been bombed with much more matter on the
| early phases of solar system history.
|
| 3) Live on earth is perfectly able to cope with a poor nutrient
| aquatic environment. Most of the earth falls exactly on this
| category after all.
|
| 4) Some life forms need just a little bit of carbon to be
| functional. Earth has very big animals that are 99% water.
|
| 5) Cold water promotes slow metabolism. Life just adapts growing
| really slow, being carried by currents, and adopting a
| poiquiloterm life style.
| vel0city wrote:
| This is talking about estimated average comet/asteroid impacts,
| right? If we're going by the average asteroid impacts on even
| million-year timescales causing radical changes to a heavenly
| body, we'd end up with no moon.
|
| I definitely get this is a limited research here, and I'm not
| faulting it for that. Its good to know it seems like this kind of
| cycle wouldn't be consistent in adding organic molecules to the
| subsurface oceans. But let's not necessarily see this as "there's
| no way organic molecules could have been pushed down in relevant
| amounts."
| deadbabe wrote:
| Uninhabitable as in we couldn't introduce basic life forms there
| even if we tried?
| gweinberg wrote:
| The article seems to treat speculation with more confidence than
| it deserves, and also to report estimates with unjustified level
| of precision. For example, it claims the annual amount of glycine
| transferred to Titan is equal to the mass of "a male African
| elephant" rather than simply an elephant.
| fnordpiglet wrote:
| I always find the metaphorical estimates in science reporting
| absurd. I don't know why the mass of a male African elephant is
| in any way more visceral than 6000 kg (btw a quick google
| search gives a band of 1800 to 6300kg, which isn't particularly
| precise). Given Titan is about 4.5 billion years old this could
| be an enormous amount of complex carbon transferred from the
| surface assuming it's more or less a one way process.
| ramesh31 wrote:
| There's always Europa
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