Saturn's moon Titan could harbor life, but only a tiny amount | Hacker News Reader

Saturn's moon Titan could harbor life, but only a tiny amount

news.arizona.edu

61 pointsgeox42 comments

> "Our new study shows that this supply may only be sufficient to sustain a very small population of microbes weighing a total of only a few kilograms at most – equivalent to the mass of a small dog," Affholder said. "Such a tiny biosphere would average less than one cell per liter of water over Titan's entire vast ocean."

Assuming for a moment that some life does exist in the subsurface ocean, I imagine it would be most likely that you would then expect to find very, very rare, but highly concentrated pockets of life?

Unfortunately I couldn't read the linked study because I was stuck in an endless CAPTCHA loop of trying to find an image of a refrigerator among a varying set of only helicopters, ships, and avocados. I feel absurd just writing that.

There's only one refrigerator per liter of images in the CAPTCHA.

And unfortunately, the GP's monitor is 2D only, so the total amount of refrigerators was zero.

> Unfortunately I couldn't read the linked study because I was stuck in an endless CAPTCHA loop of trying to find an image of a refrigerator among a varying set of only helicopters, ships, and avocados

I got through on the first try, and I block third party JavaScript with a whitelist

The one I got told to me find refrigerators and then never showed me a refrigerator. I clicked "skip" many times and it just kept going until I gave up.

I’m sorry to suggest this, but have you considered that you might be a robot?

These days it's hard to tell.

I contemplated this last night as I sat and stared at the wall while waiting for my family to wake for their morning routine. After much deliberation and calculation and running many simulations I arrived at the conclusion that I am most probably not a robot.

You probably misread it and it said to pick objects that go inside the refrigerator, so you were supposed to pick the avocados.

You don’t put avocados in a refrigerator in many countries of the world. IF you do, they will just go brown without ever becoming ripe.

I am reminded of the intersection between Indiana Jones and the Crystal Skull, and xkcd 2228:

https://tvtropes.org/pmwiki/pmwiki.php/Main/BombproofApplian...

https://m.xkcd.com/2228/

Hey, wouldn’t a refrigerator be an ideal space vessel for humans to explore Titan?

God what a fucking leap from the actual results of the study to that article title. The only thing the study indicated with even the barest hint of significance is that there is probably only a very limited amount of glycine being transported from the surface to the interior ocean. That's it.

Imagine what humanity could be capable of if we had the grace to ignore the title.

I think the most plausible takeaway is that, assuming this study is "correct", if a process would only allow a few kg of life at planetary scale then that process is not what life would rely on in that environment.

I hope there will be sirens... https://en.wikipedia.org/wiki/The_Sirens_of_Titan

Are bolide impact events the only possible mechanism for communication between ice crust and subsurface ocean? Is there no analogue to tectonism on Titan ice crust, to subduct nutrient rich ice?

Yeah the study seems to make 4 assumptions:

1.) The life's only metabolic source of energy is glycine

2.) The life is analogous to glycine metabolizing organisms on Earth

3.) The only source of glycine getting deep into the ocean is through these rare impact events

4.) The life can only survive in the deep subsurface ocean

Speaking of ocean, water is mentioned several times in discussing Titan but the hydrologic cycle analogue consists of various hydrocarbons.

But to the fourth point, I wonder to what extent radiation is a factor in mutation of biological material. It turns out Titan has a rather low surface irradiation coefficient due to being rather distant from Saturn's radiation belt, a weak induced magnetosphere (rare for moons!), and the ions are mostly water-based coming from Enceladus while Jupiter's radiation belts are largely sulphur ions coming from Io.

The hydrocarbon oceans are on the surface, but there are liquid water oceans beneath the surface.

I'm interested that their conclusion -- that Saturn could only support tiny life forms such as bacteria -- is not dependent in any way on the distance from Titan to the Sun.

Am I wrong in thinking that any life must require a steady input of energy, and that this must come from either solar energy or geothermal energy? Quick Googling says that Titan's core isn't known for sure, but probably isn't very hot.

If Titan's life were dependent of solar energy, wouldn't it's distance from the Sun imply very little energy to go around, and so very unlikely to have large organisms?

The gas giants' moons are heated quite a bit by tidal friction. They're warmer than would be expected just based on their distance from the sun.

Solar energy can be captured only by living beings that have reached a relatively high complexity after a long evolution.

In places with so little solar energy, living beings might never develop means for capturing it.

For the appearance of life, a source of internal heat for the planet or satellite is a necessary condition.

As another poster has mentioned, in the big satellites of the giant planets such a source of internal heat exists, because of the tidal forces which cause internal friction.

For the internal heat to be able to provide energy for life forms, there must exist some kind of volcanism that cycles matter between the interior and the exterior of the satellite or planet, so that substances that were in chemical equilibrium at higher temperatures are brought to lower temperatures, where they are no longer in chemical equilibrium, which can provide the energy for the synthesis of complex organic molecules.

(On Earth, the principal source of energy for the bacteria that do not depend on solar energy has its origin in the iron(II) ions from the mantle and lower crust of the Earth, which are brought by volcanism at the surface, where they are no longer in chemical equilibrium with water, so they are oxidized by water to Fe(III) ions, i.e. rust, liberating elemental hydrogen from the water, which can be consumed by bacteria and combined with carbon dioxide into organic substances, without needing any other source of energy. When rocks are recycled by subduction into the mantle, because of the high temperatures the iron ions are reduced again to Fe(II) ions, completing the cycle by consuming a certain amount of internal heat.)

Hmm, didn't cyanobacteria / blue-green algae evolve early in Earth's history? I would agree that chemosynthesis seems like a better bet so far away from the sun, though).

Relatively early but there was at least 500 million and perhaps over a billion years separating the first life and the first photosynthesis. At least as much time as between us and the Cambrian Explosion.

https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_h...

There has been a long time from the first photosynthesis until the appearance of cyanobacteria, which can oxidize water.

The first phototrophs have been able to oxidize only easier to oxidize substances, at first sulfur, then iron(II) ions, and eventually also manganese ions. The last of these, the oxidation of manganese ions, has evolved into the oxidation of water, which produces free dioxygen. The immediate ancestors of cyanobacteria had 2 different light capturing systems, presumably because one was specialized for oxidizing sulfur and the other was specialized for oxidizing manganese. After the development of the water-oxidizing capability, the 2 photo-systems have become connected in series in the modern oxygenic phototrophs, to accommodate a wider range in energy levels between that corresponding to the oxidation of the oxygen in water and that corresponding to the reducing of carbon into organic substances (and also to the reducing of nitrogen and sulfur).

Cyanobacteria have appeared only about half time from the appearance of life on Earth until today. They may have appeared only after up to a couple of billion years after the appearance of life.

Moreover, some of the signs that are considered as the earliest evidence for the activity of cyanobacteria are inconclusive, because deposits of oxidized iron can be produced not only by the appearance of free oxygen in the atmosphere, but also by direct oxidation of iron(II) ions by bacteria that are unable to produce free oxygen.

Another interesting thing is that it seems that cyanobacteria have appeared on the continents, not in the ocean, and they have invaded oceans only later.

In fresh water, the ability to oxidize water would have been critical, because fresh water did not contain abundant sulfide, iron(II) and manganese(II) ions, like the ocean, which were good enough for the earlier phototrophs.

Sure, but that's basically my point, or at least the point I thought I was making. Chemosynthesis can provide enough energy for bacteria, but to have anything much larger than bacteria you'd need a bigger source of energy, such as high solar radiation, right?

Right.

Which is why nobody expects other kind of life on Titan except bacteria-like and virus-like, but there is a non-null probability for the existence there of this kind of life, which is also the only kind of life that had existed on Earth for billions of years.

Life on Earth was dependent on chemosythesis for the better part of a billion years before photosynthesis was developed. Photosynthesis is really very complex so I think we can rule that out as an initial form of life.

Hydrothermal vents are a great source of chemical energy in the form of hydrogen, hydrogen sulfide, or other chemicals that can be reacted for energy where the come out into the sea. But you could imagine other sorts of chemical energy driven by other geologic or atmospheric processes that life might bootstrap from.

The origin of the energy provided by hydrothermal vents is the internal heat of the planet.

The reduced substances, like elemental hydrogen and hydrogen sulfide, are produced by the oxidation of the iron(II) ions from volcanic rocks, which is converted by water into rust.

The volcanic rocks contain this more reduced form of iron, because they come from higher temperatures, where their constituent minerals are in chemical equilibrium. When the volcanic rocks reach ambient temperature, the volcanic rocks are no longer in chemical equilibrium with water. This source of chemical energy powers the hydrothermal vents and the associated life.

So the conditions for the appearance of life are an internal source of heat in the planet or satellite and some form of volcanism that can bring substances from the hot deep interior to the cold surface.

Energy from tidal heating is a thing for Jovian/Saturnian moons (see Io for a particularly extreme example), so there is a possibility of a 'steady input of energy' that's neither solar nor dependent on residual core heat. I mean, something is keeping that water liquid. I fully confess to not knowing how significant for life that is on Titan (and I guess noone else is sure, either).

> The researchers specifically focused on one organic molecule, glycine, the simplest of all known amino acids.

This is such a goofy assumption. That any life on Titan would use the exact same amino acids as earth-based life. If you have no clue whether something is possible, sometimes it's better to predict nothing at all.

It’s not goofy. We find these amino acids in meteorites and it is clear that they are widespread in space. Glycine being the simplest is probably the most common and most likely to be incorporated by life. It is a good proxy for an estimate.

> This is such a goofy assumption. That any life on Titan would use the exact same amino acids as earth-based life.

I might be wrong, but I think they use this assumption because they KNOW life has already formed this way, it would be goofy to assume methods that we haven't witnessed right ?

That's still a bit goofy; it's essentially the same thing as the https://en.wikipedia.org/wiki/Cargo_cult phenomenon.

Maybe I missed the mark here but is it not similar to saying "it seems goofy to look on planets with water just because that's what life required on earth"?

I'm not in any way educated on these things but are these not basic building blocks kind of things?

We know the basic building blocks for Earth life.

We currently have zero evidence for any life off the planet, water/carbon-based or otherwise. It would likely be a mistake to assume that we're the only possible setup. Maybe life spreads primarily and very slowly in Oort clouds, and we're a bit of an abberation.

Even here on Earth, we've been surprised to find life in boiling water and miles underground.

And if they found loads of this amino acid, would you say the same thing? Science isn't about getting the best answers, it's about getting accurate answers. Now that we know all about this amino acid in relation to titan, we can follow the rabbit hole to find sources of it on Titan or we can decide to look for alternatives.

The search for water in outer space, and other life-sustaining elements, has ulterior motives.

I believe that the search for alien life is subordinate to the search for things that will sustain human life and/or industry, as we expand further outwards.

Most scientists and engineers don’t actually expect to encounter significant alien life in our solar system, and it’s merely a meme they use to tease middle-schoolers, Senators, CEOs, and naïve newspaper readers. Searching and discovering life forms would be really really fraught with terror and doom, if we indeed expected to find it when we looked.

Any natural resource that exists on a moon of Jupiter, or of Saturn or in the Asteroid Belt, and if we can exploit it and extract it and turn it into something useful, for example refueling, or life support, or repairing existing vehicles en route, or simply dragging raw materials back down the gravity well to Earth, then that is a natural resource we’ll want to investigate as we expand. Dyson spheres won’t be built in a day, but we’ll need a good start on the resource extractions real soon now.

This is the quiet part they won’t say out loud, because it’s much more exciting and non-threatening to say we’re looking for alien life forms rather than sustaining our own self-interest. But it’s all about self-interest when it comes to humans.

As a treat

A tiny wafer thin layer of life

How do they know that there wasn't already abundant amino acids in the ocean before accounting for current transfer?

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