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Saturn’s moon Titan may be uninhabitable

Titan’s ocean deep below the surface and other similar oceans inside the icy moons of the outer solar system may lack the organic chemistry necessary for life, according to a new astrobiology study.

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Titan is the largest moon of Saturn and the second largest moon in the Solar System. It is famous for being shrouded in a layer of hydrocarbon smog, and its surface is literally buried in organic compounds. But despite all this exciting chemistry, Titan is very cold – its surface temperature does not rise above -179°C. In such frost, chemical reactions for the origin of life proceed very slowly.

 

However, deep below the surface, where it is warmer (the exact depth is unknown, estimates are about 100 km), it is believed that there is a liquid ocean with a volume of 12 Earth’s. Similar oceans exist inside Saturn’s moons Enceladus and Ganymede, as well as Jupiter’s moons Europa and Ganymede.

 

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In a new study, planetary scientist Kathy Nish and an international team of scientists question the hypothesis that Titan’s ocean and other similar oceans could be habitable.

The researchers proceeded from the fact that for Titan’s ocean to be habitable, a sufficient amount of organic matter from the surface must reach the bottom for prebiological chemistry and the origin of life.

 

Organic matter reaches the surface when comets fall – they melt the ice, forming puddles of liquid water filled with organic molecules. Since liquid water is denser than ice, it sinks to the bottom. However, Niche’s models showed that the frequency of impacts was too low to provide a sufficient flow of organic matter to Titan’s ocean.

 

For example, according to scientists, only about 7,500 kg of the simplest amino acid glycine enters Titan’s oceans annually. This is the equivalent of the mass of one African elephant, distributed over the volume of 12 Earth’s oceans. To put it mildly, a drop in the ocean.

 

We assumed that the majority of molecules (65%) completely submerge to the ocean. Recent calculations show this is likely an overestimation. But even in the most optimistic scenario, the organics entering Titan’s ocean are not enough to support life there.

 

And yet other possibilities remain. On Europa, where there is almost no organic matter on the surface, hydrothermal vents are believed to exist at the bottom, releasing various compounds and triggering complex chemical reactions that can support life. Indirect evidence of the presence of carbon dioxide in Europa’s oceans was obtained by the James Webb Telescope. Could the same thing happen on Titan due to organic matter from the depths?

Nish doesn’t rule out that possibility, noting that her colleagues at an institute in Texas are studying the issue. But she emphasizes a special caveat: the internal organics on Titan may be mostly aromatic compounds, from which biomolecules such as amino acids are difficult to obtain.

 

Although direct study of these oceans is not yet available, Niche’s research opens up promising possibilities for the Dragonfly mission to Titan, on which she is co-leading. Dragonfly is scheduled to launch in 2028 and arrive on Titan in 2034. The helicopter will examine the satellite from the air and take samples for analysis. According to Nisch’s work, there may be many impact craters on the surface where organic matter mixed with liquid water, possibly kickstarting complex chemical reactions before freezing and sinking underground. By studying such sites, scientists can learn a lot about the prebiological chemistry that ultimately led to the origin of life on Earth.

 

The results of the Nisch group’s work were published in the journal Astrobiology .

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