Moons are fascinating, aren’t they? Orbiting around the planets, they seem to have undertaken the solemn oath of being together, gravitationally bounded, in the large family of ours, the Solar System. One of them, among 219 known to date, is quite interesting. Saturn’s largest moon and the second-largest in the Solar System – Titan.
One of the key motivations to explore outer space is a question, driven by an inherent human curiosity: Is life elsewhere too? Considering the immensity of the observable universe, the presence of life only on our planet doesn’t seem reasonable, even the probabilities are against the odds. In the words of the famous scientist Carl Sagan – “The universe is a pretty big place. If it’s just us, seems like an awful waste of space.”
Why is Titan in focus?
Scientists and astrobiologists have been studying a few moons of Jupiter and Saturn which have shown some promises of life-bearing compounds. Titan is one of them. Resembling Earth in some features like the presence of an atmosphere, and harboring liquid on its surface, it comes out strikingly different from the other moons in the group.
Its atmosphere is rich in nitrogen like ours, but four times denser than Earth’s, and it is the only moon in the entire Solar System to have an atmosphere. The European Space Agency’s Huygens probe that landed on the Titan’s surface in 2005 confirmed the presence of liquid on its surface in the forms of lakes, rivers, and seas, although the liquid isn’t water but mostly hydrocarbons – methane and ethane. There might be a chance that alien life could be thriving on the surface based on a life structure that we are not yet sure about.
Credits: NASA/JPL/ESA/University of Arizona
A Watery Ocean
Huygens also measured radio signals on its course of descent to Titan’s surface which led to a strong probability of a water-based ocean much deeper into its surface, around 55 to 80 kilometers beneath the ground and if it is true, it may house life in a much similar way to what we are familiar with. One of the hypotheses of life emerging on Earth has its origin in its oceans, so the subsurface oceans on Titan could give us a glimpse of how life, as we know of, came into existence.
An Unusual Finding
Last year, in Oct 2020, scientists discovered a strange molecule that has never been detected in any of the planets or their moons. It goes by the name Cyclopropenylidene (molecular formula: C3H2). This molecule has so far been found only in the regions of gas and dust abundant between the star systems which are too cold for it to react with any other molecule to form compounds. But the dense atmosphere of Titan provides it the right conditions to facilitate chemical reactions.
This molecule is of great importance because it is a cyclic or a closed-loop molecule. This enables it to form the backbone rings of DNA and RNA – yes, the same chemical structure that carries the genetic code of life itself. You might recollect a similar molecule that you would have studied in your high school – remember Benzene? C6H6? Yes, the same compound that was at the heart of many reactions in Organic Chemistry and is also the only other molecule that has been found in Titan’s atmosphere. The cyclic nature of both these molecules gives them the capability to react with other ones to create different species of compounds.
Titan, at present, is hostile to life, at least the life we know of. With the temperature being -179 degrees Celsius, one can’t imagine any life that can sustain on its surface. But the strong suggestions of subsurface water oceans and the presence of cyclic molecules raise high hopes for further development of molecules that are biologically and chemically important for life formation. And who knows, maybe 100 years later, or 200, humanity would have set up a base on Titan too, in addition to the ever enthralling Mars!!