New Research Challenges the Habitability of Titan’s Underground Ocean and Similar Moons
Titan, Saturn’s largest moon, has long been a subject of fascination for scientists due to its unique characteristics. It is enveloped in a smog of petrochemicals and boasts a plethora of organic molecules on its surface. However, recent astrobiological research suggests that Titan’s underground ocean, as well as the oceans inside other icy moons in the outer solar system, may lack the organic chemistry necessary for life.
Titan’s surface temperatures are extremely cold, reaching as low as -179 degrees Celsius (-290 degrees Fahrenheit). In such frigid conditions, chemical reactions essential for life occur at an incredibly slow pace. However, scientists believe that deep underground, where it is warmer, a massive liquid ocean exists. Estimates suggest that this ocean has a volume 12 times that of Earth’s oceans combined. Similar oceans are also believed to exist within Saturn’s moon Enceladus, as well as Jupiter’s moons Europa and Ganymede.
The presence of liquid water raises the possibility of life. However, Catherine Neish of Western University in Ontario, Canada, led an international team that challenges this assumption. The researchers argue that for Titan’s ocean to be habitable, a significant supply of organic molecules from the surface must be able to reach the ocean and facilitate prebiotic chemistry necessary for life.
The primary route for organic material to reach the ocean is through comet impacts. These impacts can melt surface ice and create pools of liquid water filled with organic molecules. As liquid water is denser than ice, it sinks into the ocean. However, Neish’s modeling suggests that the rate of impacts is not sufficient for enough organic material to reach Titan’s ocean.
For instance, Neish’s team estimates that only about 7,500 kilograms (16,534 pounds) of the simplest amino acid, glycine, reaches Titan’s ocean annually. While this may sound like a substantial amount, it is equivalent to the mass of one male African elephant spread across an ocean with a volume twelve times that of Earth’s oceans. In other words, it is barely a drop in the ocean.
“We assumed that the majority of melt deposits — 65% — would sink all the way to the ocean,” Neish explained. “Recent modeling work suggests that this is very likely an overestimate, but even in this most optimistic scenario, there is not enough organics moving into Titan’s ocean to support life there.”
However, there may be other possibilities. On Europa, where organic molecules on the surface are scarce, scientists hypothesize the existence of hydrothermal vents on the seafloor. These vents would release various molecules and trigger complex chemical reactions that could support life. The James Webb Space Telescope has even detected evidence of carbon in Europa’s ocean, suggesting that organic material may be rising from the interior onto the moon’s surface.
Could a similar process occur on Titan, with organic material originating from its interior rather than its surface? Neish does not rule out this possibility and mentions that colleagues, such as Kelly Miller at the Southwest Research Institute in San Antonio, Texas, are investigating this idea. However, she highlights a potential caveat: “One concern that has come up is whether the organics sourced from the interior would be useful for life. We think they may be primarily aromatic compounds, and it is difficult to form biomolecules — such as amino acids — from such compounds.”
While direct exploration of the oceans on these icy moons is still a distant goal, Neish’s research presents exciting opportunities for NASA’s Dragonfly mission to Titan. Dragonfly, a helicopter mission inspired by the Ingenuity Mars helicopter, is set to launch in 2028 and arrive on Titan in 2034. It will explore the moon from the air and collect samples for analysis. If Neish’s findings are correct, there could be numerous impact sites on Titan’s surface where liquid water mixed with organics, potentially sparking complex chemistry before freezing and sinking. By studying these sites, scientists could gain valuable insights into the prebiotic chemistry that led to the formation of life on Earth.
The research conducted by Neish and her team was published on February 2nd in the journal Astrobiology. While the study challenges the habitability of Titan’s underground ocean and similar moons, it also opens up new avenues for exploration and understanding the potential for life beyond Earth.