Saturn’s moon Titan may have microbes, but in extremely small numbers, simulations show

Scientists believe that Saturn’s moon Titan may have a developed biosphere, as it has a global ocean of organic matter, particularly methane. A NASA expedition planned for the 2030s using a robotic helicopter will test this. However, a new study by an international team of scientists has shown that Titan’s ability to support biological life is greatly overestimated.

Rendering of NASA’s Titan exploration helicopter. Image Credit: NASA

A team from the University of Arizona and Harvard University decided to tackle the problem from a new angle. “In our study, we focused on what makes Titan unique compared to other icy moons: its rich organic content,” explain the authors of the work published in the Planetary Science Journal. They used bioenergetic modeling to estimate the ability of simple life forms to consume the organic material available on the moon.

«”It seemed that because Titan has so much organic matter, there are enough food sources to support life,” the researchers said. “We point out that not all organic molecules can be food sources. The ocean is indeed large, but the exchange between it and the surface of the moon, where organic matter is concentrated, is limited. So we advocate a more balanced approach.”

The approach proposed by scientists is based on an attempt to reconstruct the initial conditions for the emergence of biological life on Titan. Fermentation is considered one of these conditions. It is especially active in the presence of an oxidizer, such as oxygen, as was the case in the later stages of the Earth’s development. However, fermentation, which plays a vital role in the development of biological organisms, can also occur without oxygen. This version of it is observed in many corners of space – this is a reaction involving glycine, the simplest amino acid. Thus, colonies of microbes could feed even in the harshest conditions, when organic matter left over from previous generations decomposes in the presence of glycine into compounds suitable for feeding new organisms.

A typical landscape on Titan. Image credit: NASA Cassini

Scientists have estimated Titan’s potential for organic matter to decay on its surface in the presence of glycine and for decay products to penetrate beneath the ice crust into the global ocean. They believe decay products can only get under the ice where meteorites fall. This is a rare occurrence, but it is likely the only regular food source for underwater flora and fauna on the moon. Based on the estimated volumes of nutrients entering the ocean, there is hardly enough food for half a bucket of microbes for the entire nearly 500-kilometer-thick water column — about one microbe per liter of ocean fluid.

Finding a needle in a haystack will be easier than finding microbes in the waters of Titan’s global ocean, the researchers conclude.