Methane-Based Life Forms Could Exist On Titan

http://www.iflscience.com/space/template-methane-based-life-forms-titan

Janet Fang wrote:

Nearly all living organisms on Earth have water-based structures around their cells called phospholipid bilayers. These keep water in (or out), and they shelter the insides of our cells from the rest of the world. Now, according to a study based entirely on computer modeling, small molecules in oxygen-free environments may be capable of forming compartments that resemble these lipid membranes. The findings, published in Science Advances last week, suggests that life—but “not as we know it”—is possible on worlds without oxygen. They just have to be comprised of methane-based cells.

Astronomers looking for signs of extraterrestrial life (and places where mankind might colonize one day) focus on the habitable zone, a narrow area around the sun where liquid water can exist. However, if cells weren't based on water but on methane—which has a much lower freezing point—could “life” exist in extremely cold worlds like Saturn’s moon Titan? The giant moon is spotted with seas of liquid methane and has no oxygen available for the formation of a lipid bilayer membrane.

Using computer simulations, a Cornell team led by Paulette Clancy has modeled a methane-based, oxygen-free template for life. Vesicles made from phospholipid bilayer membranes are called liposomes, from the Greek "lipos" and "soma" meaning "lipid body." So, the team created a theorized cell membrane they call an "azotosome," after the French word for nitrogen. Azotosomes are made from nitrogen, carbon, and hydrogen molecules known to exist in Titan’s seas, and they show the same stability and flexibility that liposomes do, with one major exception: Their cell membrane is capable of functioning in liquid methane temperatures of 292 degrees below zero. [-292 F, -180 C]

When the team screened for candidate compounds from those present on Titan, they found the most promising one to be acrylonitrile—a colorless, poisonous, liquid organic compound used to make acrylic fibers, resins, and thermoplastics. An acrylonitrile azotosome provides good stability, a strong barrier to decomposition, and a flexibility similar to that our phospholipid membranes.

"We're not biologists, and we're not astronomers, but we had the right tools," Clancy explains in a news release. "Perhaps it helped, because we didn't come in with any preconceptions about what should be in a membrane and what shouldn't. We just worked with the compounds that we knew were there and asked, 'If this was your palette, what can you make out of that?'"

Inspired by Isaac Asimov, study co-author James Stevenson of Cornell says: "Ours is the first concrete blueprint of life not as we know it." Their next step is to demonstrate what reproduction and metabolism might look like with oxygen-free, methane-based cells.

So what do you guys think? Does the azotosome sound plausible to some of you, and could it really survive in such a harsh methane environment?

I think it is exciting that they managed to scan for and find acrylonitriles on Titan. The idea that any kind of organic can grow on alien planets and moons - let alone on a body so close to Earth - is astonishing. How does such a thing even behave?

It's been amazing how far we've come and how much we've learned about space in the past 100 years since NASA's founding.

I don't quite think this is right. While life existing on some place like Titan is possible if there were methane-based lifeforms, there's other factors to account for, like the access to nutrients. If I am correct (and I'm no astronomer so don't quote me here) I believe Titan is covered in ice, which would prevent the sun from penetrating into these oceans of liquid methane, making photosynthetic autotrophs impossible. While there are examples of autotrophic behavior existing out of the reach of light (like in seafloor vents), chemosynthetic organisms generally require heat.

Then you have the issue of genetic code. A crucial component of DNA and RNA is oxygen (DeOXYribose nucleic acid) and oxygen makes up part of the phosphate backbone of DNA. While there have been experiments with other types of nucleotides (known as XNA), they all require oxygen, and methane is too big a molecule to replace the oxygen in the backbone. I'm not saying it's impossible, of course, but it's highly unlikely and anything that was methane-based would almost certainly never attain multicellular status.

I don't know enough about microbiology to say for certain whether it is or is not possible, but I don't think we should rule it out based on the conditions that are particular to Earth, the climate of which is very unique and has liquid water, which in itself is very rare. We've also only been exposed to limited sorts of DNA that we've only so far been able to see on Earth, so we can't quite rule out the possibility that there might be a chance of a different DNA structure that we can see outside of our planetary system. If the DNA we find then possesses oxygen, then we can form the theory that ALL life, regardless of planetary origin, requires oxygen as part of the DNA's backbone.

But we're going about this the wrong way. If the DNA does contain methane instead of oxygen, it wouldn't be DNA. We'd have to make a new name to refer to it. As well, the structure of methane-based DNA would have to change - obviously with a lot more hydrogen in it. It'd be fascinating to see a organic data structure that goes against the commonly known double-helix.

Also, I can't find any good solid answers about how well light would travel through methane ice. I can't imagine that is a thoroughly investigated topic of study. However, ice as we know it is fairly transparent. Light can travel through it pretty easy, I'm not sure where you got the idea that it couldn't. It does get a little murky, what with the crystals and however many ways the light has to travel - some of it bounces back to your eyes, some does not.

I wonder if some of the methane-based life would even explicitly require light and can obtain energy in a different way. If not, then there is still the fact that we have creatures living in Earth's deep trenches, which itself has very little to no light. Micro-organisms just beneath the surface of Titan's oceans could probably get more energy from light than what our trench-dwellers can. We even have some small organisms living and thriving in caverns. There's a lot to consider when contemplating about alien life and the prerequisites for life, and constraining ourselves to a limited set of laws and theories that were made on Earth would leave little room for a scientist's imagination.

Well while thin ice might be transparent, the thicker ice gets, the more opaque it becomes. Plus, if Titan truly did not contain any oxygen gas whatsoever, its ice would be blue ice (ice with all of the oxygen molecules removed from it) which is opaque.

EDIT: Googled it:solid methane is opaque.

I've gathered that. While there might be very little light beneath the ice encrusted over Titan's oceans, we can't really be certain until we drop a submarine/camera down there that is capable of withstanding the environment. But I'd be willing to wager there might be enough light just beneath the ice.

Perhaps. I mean, they could be chemosynthetic like deep sea organisms on Earth even though deep-sea prokaryotes are generally thermophiles. Afterall, just because it's not on Earth doesn't mean that it's true.

What I think would be interesting is an intelligent species from a place like this, as their technology would have to be so radically different. The metals that we use nowadays would be worthless to such a race and any kind of heat would kill them, so it would be extremely interesting to see how they worked.

Technology might be limited by the resources provided. Technology as we know it was also developed by mankind to improve our daily lives (see shelter, weapons, tools for moving large objects). We're looking at the development of a single potential lifeform with seemingly nothing to compete against. If there's life on Titan, I doubt it will become intelligent. At least, not without billions of years of evolution and different species of lifeforms sprouting. I'm not sure how underwater tech would even develop. Especially when you're only exposed to liquid and frozen methane, and other trace elements.

Well of course it would take millions of years, just as it did on Earth, but I could see supercold tech forming. I mean, some gasses freeze solid there and, when heated, could provide something like the electric light. That would only work while on the planet, though, as it would literally need to be colder than space.

I'd hesitate to call it an "electric" light. There would still need to be methods of heating frozen gasses inside an ocean of liquid methane, or where life is less likely to develop, on top of the frozen wasteland. Even then, it'd probably be far too cold for conventional heating methods. And if it emitted light, it'd be an ionized gas, so you'd need something to contain it. It would probably dissipate without a constant source.

While I am excited about the prospect of life on Titan, I think intelligent life might be outside its capability.

extremophilic multicellular life is hard enough to come by!

Patches wrote:

I've gathered that. While there might be very little light beneath the ice encrusted over Titan's oceans, we can't really be certain until we drop a submarine/camera down there that is capable of withstanding the environment. But I'd be willing to wager there might be enough light just beneath the ice.

certain antarctic microbes get by just fine on small amounts of light, e.g. under a glacier, though I haven't investigated deeply enough to even quantify 'how much light'. and of course y' both have already brought up other light-deprived locales.

part of the point of the antarctic microbes is that they're generally psychrophiles (some produce their own antifreeze), although this is irrelevant because Earth standards can't hold a candle to 'liquid methane'.

Patches' wrote:

It'd be fascinating to see a organic data structure that goes against the commonly known double-helix.

yes, indeed

here at home we can test what designs are even mathematically viable, by computer simulation, and that speeds/enables our search over the original astronomically-large space for things that do things besides just sit there - to put it crudely - and it's a nice thought experiment in the meantime.

More than that, if someone can produce azotosomes in the lab. Interesting that chemists came up with this. (Nice that they're heavily into modelling.) More surprising to me than it should be.

I haven't studied looked into condensed matter physics yet. Seems like that's what it takes to explain - to model? - chemistry.