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How life could develop in the methane lakes of Saturn's moon Titan

Cold and waterless, Saturn's moon Titan may be able to support life 'not as we know it.'

Scientists may be one step closer to understanding whether life could have formed in the methane lakes of Saturn's largest moon, Titan.

This life, if it exists, would look very different from life on Earth. There is no oxygen on Titan, and the surface temperature is about minus-290 degrees Fahrenheit -- so cold that under most circumstances liquid water would quickly freeze on its surface.

On the other hand, Titan is the only other body in our solar system that has liquid lakes and oceans on its surface, making it an intriguing place to look for life.  It also has a thick atmosphere and a complex weather system. 

"Methane takes the same role as water on Titan," Conor Nixon, a planetary scientist at NASA's Goddard Space Flight Center told the Los Angeles Times. "It evaporates on the surface and then rains back down."

Researchers from Cornell University wanted to know whether it was possible to create some of the basic molecular necessities of life from the exotic chemistry of this alien world.

Specifically, they wanted to know whether a flexible membrane similar to the lipid bilayer membrane that defines cellular life on Earth could form in the methane lakes of Titan.

Scientists have suggested that the lipid membranes that surround our cells were a crucial evolutionary step for life on Earth because they create flexible and semiporous containers that separate the liquid world "outside" from the liquid world "inside."

In a paper published in the journal Science Advances, the authors call this separation a "key requirement of life."

But the scientists were not sure that the formation of these flexible membranes would be possible in the Titan environment.

"Liquid methane is cold enough to solidify almost any substance," they wrote. "At such temperatures, it might seem almost impossible for a flexible organic membrane to form, let alone one with a similar flexibility to that of a lipid bilayer."

They added: "Our normal intuition needs to be adjusted for a colder world."

The Cornell research team consisted of planetary scientist Jonathan Lunine; Paulette Clancy, who specializes in molecular dynamic computations; and her graduate student James Stevenson. 

They hypothesized that membranes on Titan would rely on the polarity of nitrogen-containing groups to hold them together. They named these theorized membranes "azotosomes," which translates roughly to "nitrogen bodies."

Next, they had to find a molecule that was known to be abundant on Titan and could self-assemble into an azotosome.

Eventually they found a promising candidate in acrylonitrile, a small organic nitrogen compound that on Earth is colorless, poisonous and used in the manufacture of acrylic fibers. 

But on Titan, "it makes a nice, stable membrane structure that has elasticity to it," said Lunine. "It hit the sweet spot."

Computer models suggest that in order for acrylonitrile to organize itself into an azotosome in cold methane lakes, it has to be in a high enough concentration that its molecules collide with one another. 

Data from NASA's Cassini spacecraft have shown that acrylonitrile exists in Titan's atmosphere, but the researchers do not know whether there is enough of it in the moon's lakes and seas to form an azotosome.

"That is something one would need to further investigate," Lunine said.

He added that this work on whether the building blocks of life could spring up in a water-free environment like Titan could have implications for the search for life in our solar system and beyond.

"If the giant seas of methane and ethane on Titan can produce life or something that you can call a transition to life, that suggests life is a common outcome of chemical processes and does not rely on water," he said. 

Science rules! Follow me @DeborahNetburn and "like" Los Angeles Times Science & Health on Facebook.

 

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