The precursors to life may be on Saturn’s smoggy moon Titan, but not in the way you think. Far from there being DNA or RNA drifting around the muddy surface of his hydrocarbon-rich world, a team of scientists from Cornell University think that they have demonstrated that all you need to produce the building blocks of life is one chemical: hydrogen cyanide.
This hydrogen, carbon, and nitrogen-containing compound is found all across the cosmos, from right here on Earth to as far away as Comet 67P. As it happens, it is also found on Titan, thanks to the composition of its toxic atmosphere.
When solar radiation impacts the nitrogen and methane drifting around far above Titan’s surface, the subsequent photochemical reaction produces the compound in question, which some think may be a possible prebiotic (“before life”) chemical key. In fact, hydrogen cyanide is the most common hydrogen-containing compound in Titan’s atmosphere.
As the study notes, hydrogen cyanide – an organic chemical – can react with many other molecules, as well as itself, allowing it to form long chains known as polymers. One of these polymers is named polyimine, and the team, using a series of quantum chemical calculations, are reasonably confident that it’s on the moon’s surface.
Polyimine is a particularly bendy molecule even under very cold conditions, such as those on the surface of Titan, where temperatures average out to around -179°C (-290°F). Polyimine’s flexibility means that it can take on a variety of shapes, some of which are similar to chemical catalysts on Earth that accelerate reactions that eventually lead to the formation of the building blocks of life.
It also means that it can take the form of complex structures that “host” prebiotic chemistry, again laying the groundwork for future life to spring from. Although polyimine has yet to be directly detected on the surface of Titan, this hypothesis, as outlined in the Proceedings of the National Academy of Sciences, is one that astrobiologists the world over will be keen to find evidence for.
Trace organic gases in Titan's atmosphere – hydrogen cyanide (left) and HC3N (right). NRAO/AUI/NSF/NASA
“We are used to our own conditions here on Earth. Our scientific experience is at room temperature and ambient conditions,” Martin Rahm, postdoctoral researcher in chemistry at Cornell and lead author of the new study, said in a statement. “Titan is a completely different beast.”
Trying to work out how chemistry begets biology is, to put it lightly, remarkably difficult. We only have one example of life coming into existence and evolving – no guesses for where that may be – and after centuries of advancements in the biological sciences, the precise mechanism for the origin of life still eludes us.
Researchers are reasonably confident that life as we know it needs a few building blocks to get started, including chemicals that are the fundamental components of DNA – hydrogen, oxygen, nitrogen, carbon, and phosphorus – along with proteins and complex carbohydrates. Often, water has been thought to be essential, primarily because wherever water is found, life is found, but this study makes the incredible suggestion that this may not be the case.
A true color image of Titan's upper atmosphere. NASA