Life 'not as we know it' possible on Saturn's moon Titan

February 27, 2015 by Byanne Ju, Cornell University
A representation of a 9-nanometer azotosome, about the size of a virus, with a piece of the membrane cut away to show the hollow interior. Credit: James Stevenson

A new type of methane-based, oxygen-free life form that can metabolize and reproduce similar to life on Earth has been modeled by a team of Cornell University researchers.

Taking a simultaneously imaginative and rigidly scientific view, chemical engineers and astronomers offer a template for life that could thrive in a harsh, cold world - specifically Titan, the giant moon of Saturn. A planetary body awash with seas not of water, but of liquid methane, Titan could harbor methane-based, oxygen-free cells.

Their theorized , composed of small organic nitrogen compounds and capable of functioning in liquid methane temperatures of 292 degrees below zero, is published in Science Advances, Feb. 27. The work is led by chemical molecular dynamics expert Paulette Clancy and first author James Stevenson, a graduate student in chemical engineering. The paper's co-author is Jonathan Lunine, director for Cornell's Center for Radiophysics and Space Research.

Lunine is an expert on Saturn's moons and an interdisciplinary scientist on the Cassini-Huygens mission that discovered methane-ethane seas on Titan. Intrigued by the possibilities of methane-based life on Titan, and armed with a grant from the Templeton Foundation to study non-aqueous life, Lunine sought assistance about a year ago from Cornell faculty with expertise in chemical modeling. Clancy, who had never met Lunine, offered to help.

"We're not biologists, and we're not astronomers, but we had the right tools," Clancy said. "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?'"

On Earth, life is based on the phospholipid bilayer membrane, the strong, permeable, water-based vesicle that houses the organic matter of every cell. A vesicle made from such a membrane is called a liposome. Thus, many astronomers seek extraterrestrial life in what's called the circumstellar habitable zone, the narrow band around the sun in which liquid water can exist. But what if cells weren't based on water, but on methane, which has a much lower freezing point?

The engineers named their theorized cell membrane an "azotosome," "azote" being the French word for nitrogen. "Liposome" comes from the Greek "lipos" and "soma" to mean "lipid body;" by analogy, "azotosome" means "nitrogen body."

The azotosome is made from nitrogen, carbon and hydrogen molecules known to exist in the cryogenic seas of Titan, but shows the same stability and flexibility that Earth's analogous liposome does. This came as a surprise to chemists like Clancy and Stevenson, who had never thought about the mechanics of cell stability before; they usually study semiconductors, not cells.

The engineers employed a molecular dynamics method that screened for candidate compounds from methane for self-assembly into membrane-like structures. The most promising compound they found is an acrylonitrile azotosome, which showed good stability, a strong barrier to decomposition, and a flexibility similar to that of phospholipid membranes on Earth. Acrylonitrile - a colorless, poisonous, liquid organic compound used in the manufacture of acrylic fibers, resins and thermoplastics - is present in Titan's atmosphere.

Excited by the initial proof of concept, Clancy said the next step is to try and demonstrate how these cells would behave in the methane environment - what might be the analogue to reproduction and metabolism in oxygen-free, methane-based cells.

Lunine looks forward to the long-term prospect of testing these ideas on Titan itself, as he put it, by "someday sending a probe to float on the seas of this amazing moon and directly sampling the organics."

Stevenson said he was in part inspired by science fiction writer Isaac Asimov, who wrote about the concept of non-water-based life in a 1962 essay, "Not as We Know It."

Said Stevenson: "Ours is the first concrete blueprint of life not as we know it."

Explore further: Cassini nears 100th Titan flyby with a look back

More information: Science Advances 27 Feb 2015: Vol. 1 no. 1 e1400067

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1 / 5 (12) Feb 27, 2015
Not quite. Purple sulfur bacteria exist on earth and are not carbon based lifeforms.
4.4 / 5 (14) Feb 28, 2015

You couldn't be more wrong.

1.8 / 5 (10) Feb 28, 2015
Re : "We're not biologists, and we're not astronomers, but we had the right tools," ? ; well if they were only a molecular biologist they might not even bother to go through all these calculations and experimentations ; ; they would not even waist their time and energy and funds which they did to have a final conclusion . Because the fundamental clue to any life form in our universe is `the molecular structure of its CODE`- what we call Genome- and what it(THE CODE) should be like ? molecular vise . Thermodynamically speaking the molecular structure of it and absolute requirement to `EVOLVE` and `PRESERVE`its unique three dimensional structure in a given temperature and environment . To ZIP and UNZIP (to switch on and off three dimensional thermodynamic space ) and capability to `MUTATE` in order to evolve and survive in `ever changing environment` .All these fundamental requirements listed one by one for the mere existence of any life form in our Universe `molecula
1.8 / 5 (10) Feb 28, 2015
All these fundamental requirements listed one by one above for the mere existence of any life form in our Universe `molecular biological terms` would have been more than enough to convince anybody that the life forms as we off CAN NOT EXIST on Saturn's moon Titan '', simply because ; any life form has to meet the `UNIQUE` conditions(factors) one after another ADDITIVELY and `ALL JOINING TOGETHER` mentioned above one after another –not even a single one is missing- .
4.6 / 5 (11) Feb 28, 2015
Nice, I think at the end we will be surprised about how many ways there are for life to exist in this universe.

2 / 5 (4) Feb 28, 2015
Living organisms in any form can not exist without a data carrier, which encodes the biochemical processes in them supporting their life and their precise synchronization. This information is very complex even the simplest forms of life and no chance to occur by chance. Here shines intelligence, ideas and purpose. I do not know people as intelligent being to rely essentially on chance to make progress in its every day activity. In fact they always rely on their inteligence.
4.8 / 5 (8) Feb 28, 2015
Does the membrane have the capability to exchange material across, or is it effectively just a plastic shell?

The function of the lipid membrane in life as we know it is more than just encapsulating a cell.
1 / 5 (6) Feb 28, 2015
Somebody wants more grant money.

"Quick publish something before our supporter suspects (very possibly correctly) that we have made no progress."

A lot of questions left unanswered. Also that one analogy about the right tools. I can make a supplemental analogy for it.

A heavy duty mechanic hands an investment broker a key to his tool box and says go and reassemble that 797F. Don't worry it's only 3 stories tall.
1.8 / 5 (5) Feb 28, 2015
Also simulations mean nothing if they are found to be incompatible with how things occur in existence. This is yet to be verified up or down. Send the probe.
4.2 / 5 (10) Feb 28, 2015
"Somebody wants more grant money."

Syn 51, what is your own profession? I am always curious how others assume we all have the same ethics, that our fields of work are similar. They are not.

I am not a scientist, but would never try to get away with anything, . . in real professions, it is suicide.
5 / 5 (1) Feb 28, 2015
Wait. How about a creature that lives in intergalactic wormholes & eats dark matter? We could call it an obscurizome.
4.1 / 5 (9) Feb 28, 2015
That is interesting since akrolynitrile is simple in comparison with the first expected lipid membranes, a 3C1N lipid+nitrile chain vs 7-10C lipid chains. [ http://en.wikiped...onitrile ]

It amps up the likelihood for life on Titan analogs. However there is still a huge barrier against such due to the slow reaction rates and the absence of a suitable hereditary material.

@Eikka: Good point! Perhaps that is the "flexibility" they ascribe to their membrane vesicles.
4 / 5 (8) Feb 28, 2015
@Kedas: That is what evolution and so the diversity of our biosphere shows: But there is a reason why all life forms on Earth shares only one universal common ancestor, and that is because RNA is so far the only known heteropolymer that satisfy the thermodynamical bound when it evolves to be both a catalyst and a replicator. [See Russell et al "The Drive to Life on Wet and Icy Worlds".]

I am pretty huffed that we likely know how life emerged now, the above referenced SAH theory is 20 billion times likelier than the other theories (by way of homologies), and that we know how to test it (by way of homologies), and that it is simply evolution all the way after full grown geophysical systems by way of homologies - the modern cell remembers its ancestor due to the genome maintaing it in the extended phenotype of the cellular machinery). Who would have thought that a mere decade ago?

3.7 / 5 (6) Feb 28, 2015

But on the other hand it effectively shuts down alternative pathways as non-viable. (Or perhaps in rare cases low likelihood due to slower pathways than the one that most likely operated in us.)

Non-water, here super-cold, life seems to be among them.
3 / 5 (2) Feb 28, 2015
@T_L_OM. Please provide a reference to your claim that information must be stored, replication must occur, and catalysis must happen ONLY with/on a single heteropolymer. Thanks- sounds like someone will soon be getting a call from the Nobel Committee. I am dubious that something as non-polar as CH4 is capable of supporting the energy balance necessary, but as (unintentionally) pointed out, I made the mistake of considering only liquid water relevant reaction time-scales. When you have billions of years to work with, how fast must life live? A single thought in a millenium? Could this answer the Fermi Paradox? From paper:"Whether Titan can support any form of cell membrane is not certain. However, we do observe that Titan's surface hosts an unknown process that consumes hydrogen, acetylene, and ethane, all of which continually flow down from the atmosphere but do not accumulate." Intriguing...
5 / 5 (5) Feb 28, 2015
Not quite. Purple sulfur bacteria exist on earth and are not carbon based lifeforms.
Which live in water. The article isn't about non-carbon life forms, it's about lifeforms that exist in an environment without water.
2.3 / 5 (3) Mar 01, 2015
Nothing can replace the water in terms of living organisms. The water molecule has a unique physico-chemical properties that allow complex biochemical processes within the cell of living organisms. Another solvent does not work. That someone has shared his dreams in this article does not make it credible. With simulations can be proved everything. Depends what mathematical algorithm is incorporated in them and whether it correctly describes reality or is completely frivolous to it.

2 / 5 (4) Mar 01, 2015
@viko mix

Nothing can replace the water in terms of living organisms. The water molecule has a unique physico-chemical properties that allow complex biochemical processes within the cell of living organisms. Another solvent does not work.

You obviously didn't read the link I provided

"The purple sulfur bacteria are a group of Proteobacteria capable of photosynthesis, collectively referred to as purple bacteria. They are anaerobic or microaerophilic, and are often found in hot springs or stagnant water. Unlike plants, algae, and cyanobacteria, they do not use water as their reducing agent, and so do not produce oxygen"

1 / 5 (3) Mar 01, 2015
@ Vietvet

I do not understand why you are trying to boggle? Are you know what does mean the consept redusing agent? If you have not read definition it is never too late to do it. What is the connection between redusing agent and the main solvent in the cytoplasm of the cell, which in this bacterium is also water? I do not see such connection.
1.8 / 5 (5) Mar 02, 2015
"Somebody wants more grant money."

Syn 51, what is your own profession? I am always curious how others assume we all have the same ethics, that our fields of work are similar. They are not.

I am not a scientist, but would never try to get away with anything, . . in real professions, it is suicide.

My main employment is repairing said 797F's. But also am currently attending SAIT for power engineering.

To claim that science would never stoop to corruption is false as has been proven before. Like with the experiment that claimed particles had broken the light speed barrier.

Nobody in a profession can get away with fraud or embezzlement? Have you heard of bankers, lawyers, politicians? White collar crime is very real and yes it does occur in the scientific field.
not rated yet Mar 02, 2015
In theory or in dreams there may be many, many lifeforms. Just read the sci-fi books.
Reality is another, different matter.
4 / 5 (4) Mar 02, 2015
@Z: It is the ref already posted, as mentioned, sorry if it wasn't clear.

"Thanks- sounds like someone will soon be getting a call from the Nobel Committee."

Well, if you think 40 years or so of testing is "soon", the estimate around 10 years ago. Since the most likely pathways are high pressure, high temp, the experiments have proven more difficult than at that time too. Or maybe the consensus will swing over those homologies...

"When you have billions of years to work with,".

I would expect the reverse, the breakdown processes (chemical attack, waves, et cetera) are fast compared to the energetics driving catalytic reactions.

@viko: There are alternate liquids, and methane is one of them. Water is best, but the problem lies elsewhere.

@syndicate: Prove it.

And cheating is very obvious compared to other fields, and there are open processes correcting it.
not rated yet Mar 02, 2015
Very overblown title. A membrane analog is hardly life.
1 / 5 (2) Mar 02, 2015
This is only the tip of the iceberg.

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