科学美国人60秒:Titan Could Host Life 'Not As We Know It'

Saturn's largest moon, Titan, has a thick atmosphere. Clouds. Complex organic molecules. NASA has called it "one of the most Earth-like worlds we have found to date." With one glaring exception. "It's awfully cold down there. It's about 94 degrees Kelvin. Which means that water would be a rock."

Paulette Clancy, a chemical engineer at Cornell University. At temperatures that cold—minus 290 degrees Fahrenheit—one of the most basic biological structures, the cell membrane, can't exist. Because to form, the oily membranes depend on the presence of liquid water. 

That said, Titan does have plenty of liquid to go around—but it's liquid methane. So Clancy and her colleagues used computer models to determine whether any molecules on Titan might mimic the membrane-forming compounds here on Earth. Based on a catalog of organics observed by NASA's Cassini mission, they found a candidate: acrylonitrile. Its internal electrical charge distribution would allow it to self-assemble into membranes, just like phospholipids do here on Earth. It's similarly flexible and stable. And there's a lot of it on Titan. The findings are in the journal Science Advances. [James Stevenson, Jonathan Lunine and Paulette Clancy, Membrane alternatives in worlds without oxygen: Creation of an azotosome]

Of course just because a cell membrane could form, does not mean it will. And actual life is a good deal more complicated than just a membrane. Still, Clancy says we might do well to expand the search for life beyond just places with liquid water. "I think we tend to look for things that we know and understand. If we were more broad-minded we might find different kinds of life elsewhere. And maybe that would be fascinating too.” 

—Christopher Intagliata

[The above text is a transcript of this podcast.]