Scientists and chemical engineers at Cornell University have modeled a theoretical cell membrane that could be the blueprint of an alien life form that is unlike anything found on Earth. Flexible, permeable, requiring no oxygen and able to withstand temperatures near absolute zero, this structure could survive and potentially thrive in the extremely cold methane seas of Titan, one of Saturn’s moons which has the distinction of being the only body in the solar system other than Earth to have liquid on its surface.
Traditionally, the search for extraterrestrial life has focused on exploring planets that are in orbit around their suns at a certain distance. Known as the Goldilocks Zone, planets that are also large enough to exert enough gravitational pull to secure an atmosphere greatly increase the likelihood of water existing in liquid form.
Without water, life on Earth would not exist. In fact, the very structure of the protective membrane of all living cells, called the phospholipid bilayer, is largely made of water. The idea that alien life could develop on a world completely dissimilar to our own has been a concept astrobiologists have been trying to wrap their heads around for some time. The compartmentalization of matter inside an organic membrane is one of the key cellular evolutionary milestones in the development of life. One of the problems facing scientists who theorize about life on other worlds is figuring out what kinds of unique forms these membranes would take, and how life would exist at the most basic cellular level.
Titan and acrylonitrile
The Cassini spacecraft’s Titan flyby in 2006 provided many exciting discoveries. It also raised several baffling questions. Aside from proving the existence of Titan’s liquid methane seas, the data retrieved showed a startling discovery, namely that large amounts of hydrogen and acetylene were either missing or being consumed from Titan’s atmosphere, which could only be explained either by unknown geologic processes or life. This combination of findings can explain what led the Cornell University researchers to consider methane-based life in earnest, and to design a theoretical cell membrane that utilizes neither oxygen nor water, but could still exist on a world such as Titan. Using data from the Cassini spacecraft, the scientists ran experiments that included only those chemicals found on Titan that could possibly self assemble into a cell.
“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?” said molecular chemist Paulette Clancy.
The theoretical cells, which they named “azotosomes” or “nitrogen bodies”, consist of a nitrogen compound along with carbon and hydrogen, all of which exist on Titan. The best candidate they found for the nitrogen compound was an organic substance known as acrylonitrile, a poisonous, colorless substance used in the manufacture of acrylic fibers and resins.
Planetary scientist Jonathan Lunine said, “it makes a nice, stable membrane structure that has elasticity to it…It hit the sweet spot.”
Although acrylonitrile compounds have been found in the atmosphere of Titan, a key question is yet to be answered, does it exist in the methane seas in dense enough quantities for the acrylonitrile molecules to form azotosomes? Also, azotosomes are possible, which is amazing, but are they probable? The answer to these questions will have to wait until future missions to Titan are fulfilled, such as those capable of exploring the depths of Titan’s methane seas via some type of submarine. Hopefully, we will find that the spectrum of what constitutes life is far broader than we imagined, leading us to a new era where our search for extraterrestrial intelligence is expanded to other methane worlds.