We discussed the possibilities of life on Titan with the paper’s co-author Jonathan Lunine last month for our cover story Could there be life in Titan’s methane sea? Lunine has been working on the problem for years, having been inspired by Voyager 1’s fly-by of Titan at the beginning of his graduate career.
“Hydrocarbon life on Titan, if it exists, is so fundamentally different from aqueous biochemistry that one would immediately know it had an independent origin. How can one not be passionate about exploring this enigmatic world?” he told Cosmos.
The latest research gives a possible structure for life that could metabolise and reproduce in a similar way to life on Earth.
It was led by chemical molecular dynamics expert Paulette Clancy and first author James Stevenson, a graduate student in chemical engineering.
“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?'”
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 colourless, poisonous, liquid organic compound used in the manufacture of acrylic fibers, resins and thermoplastics – is present in Titan’s atmosphere.
Below is a graphic that first appeared in the current issue of Cosmos magazine print edition of how the mechanics of methane-based life might work. Click to expand the graphic.