Is there life on Saturn’s giant moon, Titan? The only world in the solar system other than Earth with weather and liquid on its surface, Titan has long been on a shortlist of places that could host some life. With NASA’s exciting Dragonfly mission — which will see a drone-like craft tour of Titan — due to launch in July 2028, a new study has been published that attempts to paint a realistic picture of what it can expect.
Why Titan Is Unique
NASA’s Cassini spacecraft discovered an underground ocean of water and ammonia on Titan in 2008. Although other icy moons in the solar system — notably Saturn and Jupiter — have oceans beneath their ice caps that could theoretically host life, Titan has something different. “In our study, we focus on what makes Titan unique compared to other icy moons: its plentiful organic content,” said Antonin Affholder, a postdoctoral research associate at the University of Arizona’s Department of Ecology and Evolutionary Biology.
As well as a nitrogen-rich atmosphere, rain, lakes and oceans of liquid methane, shorelines, valleys, mountain ridges, icy boulders, mesas and dunes, Titan also hosts weird prebiotic chemistry that could be the building blocks of life itself. On Titan’s surface are complex organic compounds formed from methane and nitrogen in the moon’s atmosphere. That could mean food — and life. Or maybe not.
Where Life May Exist On Titan
Titan could harbor simple, microscopic life, according to the study, published this month in The Planetary Science Journal. However, at best, it’s likely only a few pounds of biomass overall. That’s because the underground ocean on Titan — where life is most likely to exist — is over 300 miles deep and doesn’t interact much with the surface, where the organic compounds are. “There has been this sense that because Titan has such abundant organics, there is no shortage of food sources that could sustain life,” said Affholder. “Not all of these organic molecules may constitute food sources, the ocean is really big, and there’s limited exchange between the ocean and the surface, where all those organics are.” However, that doesn’t mean that life doesn’t exist — it just changes the likely mechanism.
Most Likely Scenario For Life On Titan
The researchers think that fermentation is the most likely scenario for life on Titan. Familiar on Earth as the process of producing bread, wine, beer and kimchi, the breakdown of a substance, fermentation needs only organic molecules but no “oxidant” such as oxygen. That’s entirely different from respiration, a chemical reaction found in every cell in living things on Earth, from plants to animals.
Like on Earth could have first emerged as feeding on organic molecules left over from Earth’s formation, said Affholder, adding that fermentation “does not require us to open any door into unknown or speculative mechanisms that may or may not have happened on Titan.”
‘A Small Dog’ Worth Of Microbes
In their research, Affholder and colleagues focused on one organic molecule, glycine, that could synthesize in Titan’s atmosphere, accumulate on its surface and make its way into Titan’s subsurface ocean. Could microbes in that ocean feed off glycine? It wasn’t an accidental choice — glycine exists in comets, asteroids, and gas clouds from which stars and planets are formed. It was abundant in the primordial solar system. However, the team’s computer simulations revealed that only a small amount of glycine would reach the ocean. “This supply may only be sufficient to sustain a very small population of microbes weighing a total of only a few kilograms at most — equivalent to the mass of a small dog,” said Affholder. “Such a tiny biosphere would average less than one cell per liter of water over Titan’s entire vast ocean.”
NASA’s Dragonfly mission is set to reach Titan in 2034 and will last for two years. During the mission, a rotorcraft will fly to a new location every Titan day (16 Earth days) to take samples of the organic compounds on its surface, search for chemical biosignatures and investigate the moon’s active methane cycle.
Wishing you clear skies and wide eyes.
