Extreme conditions prevail on Saturn's moon Titan. These have fascinated researchers for decades. A new study by Prof. Dr. Christian Mayer (University of Duisburg-Essen) and Dr. Conor A. Nixon (NASA Goddard Space Flight Center) now describes a process by which cell-like structures—known as vesicles—can form on Titan. Such structures are considered the first step in the emergence of life.

Titan is the only moon in the solar system with a dense atmosphere rich in nitrogen and methane. Apart from Earth, it is also the only known celestial body with lakes and seas – albeit filled with liquid hydrocarbons such as methane rather than water. These substances evaporate, form clouds, and fall back as rain. This cycle produces organic molecules called amphiphiles, which could be crucial for the formation of cell membranes.

Mayer and Nixon have developed a theoretical model based on in-depth analyses of the conditions on Titan, including the atmosphere, temperature, pressure conditions, and molecular behavior. This is supplemented by laboratory simulations and findings from previous experiments.

According to this model, the process could proceed as follows: When methane rain hits Titan's lakes and creates spray, tiny droplets are formed that are enveloped by a layer of amphiphiles. When they hit the liquid surface again, their shells combine with the lake's molecular layer to form a stable double membrane. This creates vesicles – cell-like shells that enclose liquid.

“In their environment, these structures can absorb additional molecules and thus become more stable,” explains Mayer. “The more stable vesicles survive longer – a kind of molecular competition arises, enabling an early form of evolution. That would be a first step toward protocells, the precursors of living cells.”

The researchers also propose experimental approaches to replicate this mechanism in the laboratory in the future – for example, using liquid methane under Titan-like conditions. They also recommend measurement methods for space probes, such as a combination of laser scattering and Raman spectroscopy, to detect vesicles directly in the lakes of Saturn's moon.

“The formation of vesicles under non-life-like conditions would show that the basic principles of biological self-organization are not tied to water or Earth-like conditions,” says Mayer. “This opens up completely new perspectives for astrobiology – and for our idea of where life can arise.”

Mayer and Nixon are eagerly awaiting the NASA Dragonfly mission, which is scheduled to launch in July 2028 and will conduct extensive surface measurements on Titan and collect atmospheric and geophysical data – once the rocket has landed in 2034.
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Further Information:
Prof. Dr. Christian Mayer, Physical Chemistry, christian.mayer@uni-due.de