Titan, Saturn's largest moon, is unique in our solar system for its hydrocarbon landscapes and subsurface ocean. This world features methane lakes, a dense atmosphere, and complex organic chemistry. However, not all its organic molecules would be usable by potential microorganisms.
The subsurface ocean, nearly 300 miles (500 km) deep, could harbor life based on fermentation. This simple process, which doesn't require oxygen, is one of the most plausible in such an environment.
Exchanges between the surface and the ocean are limited. Only meteorite impacts could transport nutrients through the icy crust, drastically reducing available resources.
A tiny biomass despite abundant organic reserves
The study focused on glycine, a simple amino acid found throughout the Solar System. Simulations show its delivery to the ocean would be too limited to sustain significant life.
At best, the total biomass wouldn't exceed a few kilograms—less than one cell per liter of water. This estimate makes detecting potential life extremely challenging for future missions.
Researchers emphasize that Titan's organic richness doesn't guarantee habitability. NASA's Dragonfly mission will need to target very specific areas to maximize its chances of discovery.
Going further: What is fermentation, a key process for life on Titan?
Fermentation is a metabolic reaction converting organic molecules into energy without oxygen. It's notably used in bread or beer production.
This mechanism, which appeared early in Earth's life history, requires only simple conditions. On Titan, it could allow microbes to survive with minimal nutrient input.
Unlike respiration, fermentation doesn't depend on oxidants, which are rare on Titan. It's thus a credible lead to explain potential life in its subsurface ocean.
Why is Titan so intriguing to astrobiologists?
Titan combines a dense atmosphere, active organic chemistry, and a liquid ocean. These traits make it a cold analog of early life stages on Earth.
Its hydrocarbon lakes and methane rainfall offer unique processes in the Solar System. These interactions could promote prebiotic reactions, even without confirmed life.
The Cassini-Huygens mission revealed its geology, while Dragonfly will directly study its surface starting in 2034.
Article author: Cédric DEPOND