A recent study indicates that methane gas might be encapsulated within the icy surface of Saturn’s moon Titan, creating a unique crust that can be as thick as six miles. This crust could warm the ice layer beneath it and help to explain the moon’s atmosphere rich in methane.
Titan, Saturn’s largest moon, stands out as the only celestial body, besides Earth, known to possess an atmosphere and liquid bodies such as rivers, lakes, and seas on its surface. The extreme cold on Titan means that these liquids are composed of hydrocarbons, including methane and ethane, while the surface itself is primarily solid water ice. A recent study conducted by planetary scientists from the University of Hawai’i at Manoa suggests that methane gas could be contained within the ice, resulting in a substantial crust that heats the ice shell below and might also help clarify Titan’s methane-filled atmosphere.
The research, led by Lauren Schurmeier, a research associate, along with doctoral candidate Gwendolyn Brouwer and Sarah Fagents, associate director and researcher at the Hawai’i Institute of Geophysics and Planetology (HIGP) within the UH Manoa School of Ocean and Earth Science and Technology (SOEST), discovered through NASA data that the impact craters on Titan are much shallower than anticipated. To date, only 90 impact craters have been identified on Titan.
“This was quite surprising because, compared to other moons, we expect to find a greater number of impact craters on Titan’s surface, and those craters would generally be deeper,” explained Schurmeier. “We concluded that a unique aspect of Titan must be causing these craters to become less deep and to vanish swiftly.”
To uncover what might lie beneath the surface, the research team utilized computer models to examine how Titan’s surface topography could change after an impact if a layer of insulating methane clathrate ice—solid water ice with methane gas trapped in its crystal structure—was present. Since the original shape of Titan’s craters is unknown, the researchers simulated and compared two likely initial depths based on the appearance of newly formed craters on Ganymede, a similarly sized icy moon.
“By using this modeling technique, we were able to estimate the thickness of the methane clathrate crust to be between five to ten kilometers [around three to six miles], as simulations using that thickness produced crater depths that closely matched those observed,” Schurmeier stated. “The methane clathrate crust not only warms Titan’s interior but also results in remarkably rapid changes in the surface, leading to the shallowing of craters at a pace akin to that of quick-moving warm glaciers on Earth.”
Methane-rich atmosphere
Determining the thickness of the methane ice shell is crucial because it may shed light on the origins of Titan’s methane-rich atmosphere. This information is essential for researchers studying Titan’s carbon cycle and its methane-based “hydrological cycle,” as well as its evolving climate.
“Titan serves as a natural laboratory to explore how the greenhouse gas methane circulates and warms the atmosphere,” remarked Schurmeier. “On Earth, methane clathrate hydrates found in Siberian permafrost and beneath the Arctic seafloor are currently destabilizing and releasing methane. Insights from Titan could play a significant role in understanding similar processes occurring on Earth.”
Structure of Titan
The surface features observed on Titan align with these new findings. The estimation of the methane clathrate ice crust’s thickness suggests that Titan’s interior is likely warm, rather than cold, rigid, and inactive as previously believed.
“Methane clathrate is more robust and provides better insulation than standard water ice,” Schurmeier noted. “A clathrate crust insulates the interior of Titan, making the water ice shell warm and pliable, and implies that Titan’s ice shell is or was gradually convecting.”
“If any form of life exists in Titan’s ocean located beneath the thick ice shell, any indicators of life (biomarkers) would need to be transported upward through Titan’s ice shell to be accessible for future missions,” Schurmeier added. “This is more likely if Titan’s ice shell is warm and undergoing convection.”
With NASA’s Dragonfly mission set to launch toward Titan in July 2028 and reach it by 2034, researchers will soon have a chance to conduct close-up studies of this intriguing moon and examine its icy surface, including a crater known as Selk.
