There is a new possibility for life on Titan. Scientists affiliated with Cornell University have created a blueprint for a cellular lifeform that wouldn’t need water to survive.
Water on Earth has been the principal ingredient of, as well as the catalyst for, the formation of life. The Cornell scientists believe water could be replaced by methane on Saturn’s moon Titan, where there are seas full of liquid methane.
The scientists’ work essentially lies in finding a suitable alternative for the phospholipid bilayer, a double-layer of fatty acids that constitutes every cell’s membrane on Earth. Because Titan’s atmosphere is rich in nitrogen and methane, their analysis suggested that a combination of the two molecules could create acrylonitrile azotosome, which when stacked together tends to assemble in membrane-like structures.
Acrylonitrile, it turns out, is already present in Titan’s atmosphere. What’s more is that the molecule could be reactive in the moon’s dreadfully cold environment (at -292 to -180 degrees Celsius). The next step is to see if cells with azotosome membranes can reproduce and metabolize in the methane- and nitrogen-rich environment. Their findings were published in Science Advances on February 27.
Incidentally, the formation of azotosomes also requires some hydrogen. This is interesting because astrobiologists have recently shown that the surface of liquid methane lakes on Titan could be host to microbes that metabolize acetylene, ethane and some other organic compounds, along with hydrogen.
Astrobiologists from the NASA Ames Research Center, who did this research, presumed that the microbes would need to consume hydrogen to make their metabolic reactions work. And because there is no other known process on Titan that could reduce the concentration of atmospheric hydrogen in the moon’s lower atmosphere, their calculations gave other astronomers an intriguing way to interpret anomalous deficiencies of hydrogen. Such deficiencies were recorded on Titan in 2010 by the NASA’s Cassini space probe.
There is an alternative explanation as well. Hydrogen may also be involved in chemical reactions in the atmosphere spurred by the bombardment of cosmic rays. Only continued observation will tell what is actually eating Titan’s hydrogen.
Yet another possibility for life on the moon was conceived in August 2014, when Dirk Schulze-Makuch, an astrobiologist from Washington State University, reported in Science that methane-digesting bacteria had been found in a lake of asphalt in Trinidad. The water content of the lake was only 13.5%. Schulze-Makuch suggested that, even if very little water was present on the moon, it would be enough to encourage the formation of these bacteria. What he couldn’t account for was the substantially lower temperature at which these reactions would need to occur on, say, Titan.
Slowly there has been a mounting number of possibilities, which suggest that life on Titan needn’t have to be fine-tuned or capitalize on one or two narrow windows of existential opportunity. Instead, there exist a variety of routes through which enterprising molecules could aspire for self-organization and awareness, even in an oxygen-deficient, methane-rich environment.