There’s nothing like the possibility of finding exotic alien life to motivate the exploration of our solar system. If NASA’s new concept submarine is going find anything interesting swimming in Titan’s Kraken Mare sea, it will likely be something that is happy in liquid methane at -290 degrees Fahrenheit. A group of researchers from Cornell have obliged this somewhat dreamy agenda, and whipped up a new potential basis for life that might meet these demanding requirements — and potentially reinvigorate our fading destiny to visit companion worlds.
The ‘RNA world,’ which many terrestrial origin-of-lifers have imagined for Earth, suffers from what we might call narrow perspective. As a high-level prescription lacking in generality, it is much too parochial in its reach as a potential description for all life in the universe. In other words, we need something more basic to guide our search. The so-called ‘lipid world’ attempts to replace the metabo-informational RNA world with something more geometrical — a compartmentalized ordering capable of sponsoring the microscale energetic gradients enlightened minds now see as the true generators of life.
The fragile vegetable oil membranes that higher life forms use here clearly won’t cut it in gen pop over in Kraken Mare. The Cornell researchers therefore turned to their computers to try to create something that would have the requisite suppleness to evolve the exquisitely folded nooks and crannies we hold so dear. Using spectroscopic data from the Cassini orbiter, they came up with a few potential raw materials that would be expected to naturally form by the interaction of UV light with a thick methane- and nitrogen-rich atmosphere.
In contrast to our nonpolar lipids that shun polar water, a material that could spontaneously sculpt itself into membranes and vesicles in nonpolar methane would be expected to be polar. As shown below, the ideal methane membrane material would be opposite in this respect to lipids — its polar heads would meet in the center, while the nonpolar tails would interface with the methane. The researchers found that vesicles made from acrylonitrile, an important material used in ABS plastics (like that in your mouse, keyboard, and computer), could do this. Not only that, but these ‘azotosomes’ as they now call them, were found to have similar elasticity and bending properties in cryogenic methane, as lipids have in water.
If you would suppose that all this, while curious, might be just a bit too contrived to justify a semi-autonomous Titan-shot, you may not be alone. It undoubtedly takes more than flexibility to make life. Fortunately, computer simulations, and hopefully upcoming physical experiments to vet this first-rate new theoretical work, are much less expensive than space missions. In defense of these efforts, we might take a quick tutorial look at a unique and ubiquitous class of life right here on earth. Many bacterial citizens of kingdom Archaea are what you call extremophiles, inhabitants of tough environments like hydrothermal vents and thermal springs.
One of the main differences between us and them is that they have substituted out the hydrocarbon tails of their membrane units and instead use molecules known as isoprenoids. Curiously, they also use mirror-image glycerol molecules for their membrane headgroups. Clearly life here has the wherewithall to fine-tune its protomolecular toolkit to meet the demands of its environment. If it has taken hold elsewhere in the solar system, it might not be such a stretch to expect that it could do the same there.