Cold-Resistant Compound May Be Key to Life in Titan's Methane Lakes
Liquid water has long been the holy grail in the search for extraterrestrial life, but recently, more and more astrobiologists are trying to expand the search parameters. Now, researchers have managed to simulate a compound that could potentially survive the cold, anoxic environment in Titan's methane lakes, indicating that Saturn's moon could harbor extraterrestrial life.
In the abstract of the paper, the authors directly address the possibly erroneous assumption that life is accompanied by the presence of liquid water:
The lipid bilayer membrane, which is the foundation of life on Earth, is not viable outside of biology based on liquid water. This fact has caused astronomers who seek conditions suitable for life to search for exoplanets within the "habitable zone," the narrow band in which liquid water can exist. However, can cell membranes be created and function at temperatures far below those at which water is a liquid?
Their tentative answer is "yes," as they were able to "create," through computer simulations, a cell membrane that allowed carbon-based life to survive without oxygen and resist Titan's temperatures, which are far too low to support life as we know it. The methane cell, dubbed an "azotosome," has a membrane that is built from nitrogen-based, cold-resistant compounds. They found that azotosome formed a hollow ball that behaves in much the same way as Earthly liposomes, which form the membranes in our own cells. They are flexible and able to survive stretching, poking, and twisting, which is key to the evolution of complex cellular behavior. The azotosomes retain this flexibility even in the cold, which led the researchers to believe that they could withstand the specific conditions on Titan.
"At least in a computer simulation, one can build structures of a size and geometry [roughly] equivalent to the containers that were on the Earth when life began," planetary physicist and study co-author Jonathan Lunine said to Scientific American. "You can do it with materials that we know are present on Titan...So we've presented potentially one step toward the evolution of life under Titan conditions."
Of course, this study is still just a simulation, and there's no concrete evidence that these azotosomes, or any comparable molecules, have actually formed on Titan. In order to determine whether there is life on Titan with any degree of certainty, we would need to send a probe to the frozen moon. Study co-author Jonathan Lunine of Cornell told Forbes that he hopes to "someday sending a probe to float on the seas of this amazing moon (Titan) and directly sampling the organics."
As luck would have it, NASA is in the process of planning a mission to Titan:
But even if there isn't life on Titan specifically, this study could widen the search for extraterrestrial life considerably. If we could potentially find life on planets with extremely low temperatures, then we wouldn't need to limit ourselves to the "Goldilocks zone." According to chemical engineer and co-author Paulette Clancy, searching for life on frozen planets is comparable to "trying to make an omelet without any eggs. It sort of redefines how you think about an omelet."