Click to enlarge — Azotosome, the theorized cell membrane on Titan
Liquid water is a requirement for life on Earth. But in other, much colder worlds, life might exist beyond the bounds of water-based chemistry.
Taking a simultaneously imaginative and rigidly scientific view, Cornell 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 that metabolize, reproduce and do everything life on Earth does.
Their theorized cell membrane, composed of small organic nitrogen compounds and capable of functioning in liquid methane temperatures of 292 degrees below zero, is published in Science Advances…The work is led by chemical molecular dynamics expert Paulette Clancy…with first author James Stevenson, a graduate student in chemical engineering. The paper’s co-author is Jonathan Lunine…the College of Arts and Sciences’ Department of Astronomy…
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.
In part, Stevenson said he was inspired by science fiction writer Isaac Asimov, who wrote about the concept of non-water-based life in his 1962 essay, “Not as We Know It.” I think we can conclude as Asimov would – intelligence formed of life “not as we know it” – but with science grounded in material reality, will develop an understanding of science identical in premises as any of our own species’ physical scientists. Leading or trailing one another the results must be the same since material reality remains the same.
Perceptions can vary widely. An intelligent lifeform evolved through differing chemistry wouldn’t be likely to have the same senses or senses arrayed in the same hierarchy. The possibilities are intriguing.
Truly, a worthwhile adventure. I wish them well.
“Methane on Mars Hints Life Existed on the Planet: NASA” http://www.ndtv.com/world-news/methane-on-mars-hints-life-existed-there-nasa-743214
“Life as We Know it Exists in Saturn’s Moon Enceladus Most Probably, NASA” http://www.esbtrib.com/2015/03/15/7535/life-as-we-know-it-exists-in-saturns-moon-enceladus-most-probably-nasa/ Welcomed with great anticipation by planet earth, the news is.
“Spacecraft finds “magic island” in hydrocarbon seas of Titan : World’s tantalizing oceans may teem with “weird life” we cannot begin to imagine.” http://arstechnica.com/science/2016/03/spacecraft-finds-magic-island-in-hydrocarbon-seas-of-titan/
Tallest Peak on Saturn’s Huge Moon Titan Identified (Photo) http://www.space.com/32370-saturn-moon-titan-tallest-mountain-photo.html
“The Prospects for Alien Life on Titan Keep Getting Better” http://gizmodo.com/the-prospects-for-alien-life-on-titan-keep-getting-bett-1783222440 Includes link to “Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan” in the Proceedings of the National Academies of Sciences (May 20, 2016)
“Titan is the only place in the solar system, except Earth, where rainfall and seasonally flowing liquids erode the landscape. Whereas the surface pressure is similar to that of Earth, the temperature is extremely low and the dominant liquids are methane and ethane. This makes Titan a test case for exploring the environmental limits of prebiotic chemistry and addressing the question of whether life can develop without water. Experimental and observational data suggest that hydrogen cyanide, the most abundant hydrogen-bonding molecule in Titan’s atmosphere, may polymerize on the surface to polyimine. Using quantum mechanical calculations, we show that polyimine has interesting electronic and structural properties that could potentially facilitate prebiotic chemistry under cryogenic conditions akin to those on Titan.” http://www.pnas.org/content/early/2016/06/29/1606634113
“With a suspected subterranean sea of liquid water, oceans of methane on the surface and an atmosphere that could give rise to non-water-based life, it’s no surprise that scientists are keen to learn more about Saturn’s moon Titan. To that end, a new joint project between the Global Aerospace Corporation (GAC) and Northrop Grumman Aerospace Systems (NGAS) is developing a new exploration vehicle designed to soar through the skies of that mysterious moon.
The proposed Titan Winged Aerobot (TWA) is inspired by Northrop Grumman’s T-LEAF (Lifting Entry Atmospheric Flight) class of vehicles, which would allow the craft to gently enter the atmosphere before transitioning into flight mode. Once there, the TWA would operate like a hybrid balloon and glider, utilizing a unique buoyancy system to allow it to ascend and descend without the use of propulsion systems or flight control surfaces. Minimal moving parts means it could squeeze more juice out of a single radioisotope power source.” http://www.gizmag.com/titan-winged-aerobot/44246/
Scientists just found the most basic ingredients for life bursting from an ocean on Saturn’s moon Enceladus. https://www.sciencealert.com/nasa-just-revealed-enceladus-really-does-contain-the-building-blocks-of-life
A new analysis of NASA data reveals the presence of organic compounds in the plumes of liquid water that shoot into space from the ocean below Enceladus’s icy crust.
These compounds, which carry nitrogen and oxygen, play a key role in producing amino acids - complex molecules that serve as the building blocks of proteins. Without proteins, life as we know it on Earth couldn’t exist.
Scientists have long suspected that the ocean below Enceladus’s surface could harbour the ingredients for life. Researchers had detected other organic molecules coming from the icy moon before, but this is the first time anyone has detected them dissolved in the water.
That’s critical, since it means the compounds could undergo deep-sea chemical reactions that produce amino acids.
These findings were published Wednesday in the journal Monthly Notices of the Royal Astronomical Society.
“Scientists on Monday unveiled the first global geological map of Saturn’s moon Titan including vast plains and dunes of frozen organic material and lakes of liquid methane, illuminating an exotic world considered a strong candidate in the search for life beyond Earth.” https://www.sciencealert.com/we-finally-have-a-global-geological-map-of-saturn-s-moon-titan
The map was created seven years before the US space agency is set to launch its Dragonfly mission to dispatch a multi-rotor drone to study Titan’s chemistry and suitability for life. Dragonfly is scheduled to reach Titan in 2034.
First Global Geologic Map of Titan: https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA23174
JPL (Jet Propulsion Laboratory) is a federally funded research and development center managed for NASA by Caltech.