April 10, 2025: A Tiny Biosphere Implying Fermentation In The Presumed Subsurface Ocean Of Titan ?
A new research work entitled "The Viability of Glycine Fermentation in Titan's Subsurface Ocean", published in The Planetary Science Journal by the American Astronomical Society on April 7, 2025 and proposed by a team of planetologists involving Antonin Affholder and Peter Higgins reveals the potential mechanisms that are likely to allow the development of a lifeform based on fermentation processes in the presumed subsurface ocean of Titan. Organics can form in the atmosphere and on the surface of the giant moon of Saturn. Impact events related to meteorites or comets can engender the development of pools beneath the surface and can engender migrations of materials from the soil to the interior of that world. Interactions between the hydrocarbons or the organics of the upper layer and the potential pockets of liquid water may engender more complex molecules such as amino acids that can migrate toward the presumed subsurface ocean rich in liquid water. The researchers of the study tried to evaluate the likelihood of a biosphere related to the exchanges of organics or carbon-made molecules between the core, the hypothetical subsurface ocean and the upper layer of the Opaque Moon.
The potential biosphere of the presumed subsurface ocean of Saturn's largest moon may be based on fermentation processes. The planetologists suggest that glycine fermentation is a potential metabolism occurring beneath the icy crust of that world. Glycine appears to be the simplest amino acid we know and amino acids are the building blocks of life on Earth. In the hypothetical subsurface ocean of Titan likely devoid of any oxygen, anaerobic fermentation processes can be considered because those processes don't rely on oxygen. The team of Antonin Affholder resorted to bioenergetic modeling in order to evaluate the potential presence and the potential extent of that type of biosphere. It turns out that the conditions beneath the external crust are likely to allow the presence of glycine fermentation and it also appears that those types of processes are closely related to the temperature factor. Any biosphere based on glycine fermentation would have to face a slow or limited delivery of glycine via impact melt pools. In the presumed subsurface ocean of water found beneath the external crust of Titan, any potential biosphere may be extremely poor in terms of mass due to the relatively limited amount of carbon-based molecules coming from the surface or the core.
The research work reveals that a total population of 10^14-10^17 cells representing a few kilograms of carbon can be envisaged in that huge subsurface ocean that may be as deep as 300 miles (around 483 kilometers). As a result, the concentration of that potential biosphere may be extremely limited since it represents less than 1 cell per kilogram of water if it appears everywhere in that liquid layer. Can we envisage a biosphere that is concentrated in particular environments like pockets of liquid water beneath the presumed icy crust of the giant moon ? Can we envisage other processes to bring organics, hydrocarbons or amino acids to the liquid layer dominated by liquid water ? The researchers must be in a position to characterize the various types of metabolism such as the degradation of acetylene or the degradation of polyaromatic hydrocarbons in order to produce a better quantitative bioenergetic modeling. On Earth, life can be found in the abyss thanks to black smokers or hydrothermal activity and thanks to the fall of organics from the level of the surface. We are aware that life can be found in surprising environments such as below the ice sheet in the Arctic or in the Antarctic.
The Cassini-Huygens mission has clearly demonstrated that Titan unveils a diverse landscape and a complex atmosphere relatively rich in hydrocarbons and organics. The atmosphere of the giant moon of the Gas Giant Saturn is dominated by nitrogen like the atmosphere of the Earth. But the atmosphere of Titan reveals several particularities like the atmosphere of the Earth. Oxygen is absent or almost absent in the atmosphere of Titan whereas it represents a significant fraction of the composition of our atmosphere. The opaque atmosphere of the giant moon contains a relatively significant concentration of methane, a simple molecule containing the carbon element. The concentration of methane can represent around 5 percent of the atmospheric composition at the level of the surface. There is also a global haze rich in hydrocarbons and organics that can produce relatively complex molecules rich in carbon under the influence of ultraviolet light from the Sun that interacts with the various elements, ions or molecules found in the upper atmosphere of that world. Heavier molecules will tend to fall toward the surface to form a brown or dark mud or sludge called tholin. One can imagine that the soil of Titan is relatively rich in hydrocarbons or organics.
In the complex atmosphere of Saturn's largest moon, there is a methane cycle comparable to the water cycle of the Earth. Methane can be present in its liquid form on Titan. Lakes, seas and rivers have been identified in the high latitudes of the moon thanks to the radar views and the infrared or near-infrared views acquired from the Cassini orbiter during its long mission in the Saturn System from 2004 to 2017. Clouds have also been found in the high latitudes or in the middle latitudes of the giant moon. Those observations demonstrate that methane can condense and form clouds on Titan. There are evaporation processes, condensation processes and precipitation processes on Titan like on Earth. However, the concentration of methane on Titan has nothing to do with the concentration of water on Earth. Liquid areas dominate the surface of the Earth whereas liquid areas represent a much smaller fraction of the surface of Titan. Curiously, the lakes, seas and rivers are mostly concentrated in the high latitudes or in the polar areas on Titan. Is there an internal network of pockets of methane beneath the presumed icy crust of that world or is there a layer of liquid methane beneath the external crust of Titan ? That's a major question !
In the diverse landscape of Titan where environmental temperatures are extremely low, evolving around -179 degrees Celsius, -290 degrees Fahrenheit or 94 Kelvin, several types of hydrocarbons can be found in their liquid form. That's the case for methane, ethane and propane. Clouds of methane or ethane have been clearly identified so far. Therefore, the lakes, seas or rivers of that world can be composed of a mixture of methane and ethane depending on the season, depending on the area or depending on the depth. Planetologists are trying to imagine or to anticipate the type of chemistry one could encounter in that type of liquid environment. Can amino acids, sugars or lipids emerge and develop in those pools or rivers dominated by liquid hydrocarbons ? Can the liquid migrate downward toward the presumed subsurface ocean dominated by liquid water ? Any development of complex molecules on Titan may be much slower than on Earth due to the extremely low environmental temperatures that significantly limit chemical reactions. Life based on liquid water can't be envisaged at the level of the soil because water is frozen on the surface and rocks or pebbles of water on Titan can be compared to rocks or pebbles of silicon dioxide on Earth.
The researchers envisage a configuration in which the potential biosphere of Titan could only represent a few pounds of biomass or a few kilograms of biomass. The biosphere would be composed of particularly simple organisms, tiny creatures or microscopic life and the various interactions would be particularly limited due to their relatively limited population and due to the large volume of liquid in which they are likely to evolve. The planetologists must evaluate the level of organics or hydrocarbons from the atmosphere and the soil that can reach the presumed subsurface ocean in order to evaluate the potential concentration of living organisms in that extreme environment. Any lifeform in that subsurface layer of liquid water would probably have to face the absence of oxygen. Therefore, it would likely rely on fermentation processes since respiration processes based on oxygen could not be envisaged. However, the hypothesis of an ecosystem involving carbon dioxide, oxygen, methane and water in that mysterious environment can't be ruled out even if it is unlikely. Hydrothermal activities inside the presumed internal ocean can bring surprises in terms of biology because the geysers, the volcanoes or the cryovolcanoes can bring a lot of energy and are likely to boost chemical reactions.
Titan is likely to tell us a lot regarding the chemistry of organics, the chemistry of hydrocarbons and the chemistry of life in general. Titan can engender complex hydrocarbons or complex organics. Titan can also tell us a lot regarding the boundary between abiotic organics and biological systems. The chemistry of Titan has likely engendered various complex molecules such as amino acids. The exploration of the Solar System has demonstrated that amino acids such as glycine can be found on the surface of asteroids or comets for instance. That's also the case for interstellar clouds that can reveal those types of molecules. The team of Antonin Affholder imagined glycine-consuming microbes in the presumed subsurface layer of liquid water. Those microbes would not be numerous at all due to the limited supply of amino acids from the soil and the atmosphere. The biomass would probably be equivalent to the mass of a small dog. The concentration of that biosphere in the subsurface ocean would be so low that it would represent around one cell per liter of water in the giant ocean of the Opaque Moon. The ambitious Dragonfly mission with its exploration rotorcraft is likely to bring major clues regarding the mysterious chemistry of organics and hydrocarbons found at the level of the surface on Titan.
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The image in the upper part of the table represents a portion of Saturn's largest moon Titan obtained on August 22, 2005 from the eye of the Cassini orbiter. The view whose file name is N00039033.jpg was acquired on the basis of the CL1 filter and on the basis of the UV3 filter. The image had not been validated or calibrated at the time of the observation and a validated or calibrated version of the original image had to be archived with the Planetary Data System proposed by NASA. One can clearly notice the upper atmosphere where a datached haze layer can be clearly identified. Ultraviolet light from the Sun interacts with the various elements, ions or molecules found in the upper atmosphere to form new molecules such as organics that can fall toward the surface. The image in the lower part of the table represents a colorized version of the original view. Credit for the original view: NASA/JPL-Caltech/Space Science Institute. Credit for the colorized version of the original image: Marc Lafferre, 2025. |
- To get further information on that news, go to: https://news.arizona.edu/news/saturns-moon-titan-could-harbor-life-only-tiny-amount-study-finds?_gl=1*1vjg1e0*_gcl_au*ODQ0OTUyNjYuMTc0NDQwMDE2OQ..*_ga*MTg2NTc3MjQ5NC4xNzQ0NDAwMTcw*_ga_7PV3540XS3*MTc0NDQwMDE3MC4xLjAuMTc0NDQwMDE3MC4wLjAuMTI5OTY2MTA2NQ.. and https://iopscience.iop.org/article/10.3847/PSJ/adbc66.