Saturn's moon Titan may have thick insulating methane ice crust up to six miles

Los Angeles CA (SPX) Oct 28, 2024
Saturn's largest moon, Titan, stands out as the only celestial body besides Earth with a dense atmosphere and surface liquids, such as rivers, lakes, and seas. Due to its frigid environment, these liquids comprise hydrocarbons like methane and ethane, while Titan's surface primarily consists of solid water ice. Recent findings led by planetary scientists at the University of Hawai'i at Manoa suggest that methane gas could also be embedded within Titan's ice crust, creating an insulating layer up to six miles thick that warms the ice shell beneath and possibly accounts for the moon's methane-rich atmosphere.

Research associate Lauren Schurmeier, alongside doctoral candidate Gwendolyn Brouwer and researcher Sarah Fagents of the Hawai'i Institute of Geophysics and Planetology (HIGP) within UH Manoa's School of Ocean and Earth Science and Technology (SOEST), examined data from NASA showing Titan's impact craters are unusually shallow, with only 90 identified across its surface.

"This was very surprising because, based on other moons, we expect to see many more impact craters on the surface and craters that are much deeper than what we observe on Titan," Schurmeier explained. "We realized something unique to Titan must be making them become shallower and disappear relatively quickly."

To explore this mystery, the team used computer modeling to analyze how Titan's topography might change after an impact if the ice shell was covered by a layer of methane clathrate ice, which incorporates methane gas within its crystal structure. With limited information on Titan's original crater shapes, they based their simulations on similar-sized fresh craters on Ganymede, another icy moon, and tested various initial depths.

"Using this modeling approach, we were able to constrain the methane clathrate crust thickness to five to ten kilometers [about three to six miles] because simulations using that thickness produced crater depths that best matched the observed craters," Schurmeier noted. "The methane clathrate crust warms Titan's interior and causes surprisingly rapid topographic relaxation, which results in crater shallowing at a rate that is close to that of fast-moving warm glaciers on Earth."

The potential methane clathrate crust is significant not only for its insulation properties but also for understanding Titan's methane atmosphere and carbon cycle, which resemble a methane-driven "hydrological cycle" distinct from Earth's.

"Titan is a natural laboratory to study how the greenhouse gas methane warms and cycles through the atmosphere," Schurmeier remarked. "Earth's methane clathrate hydrates, found in the permafrost of Siberia and below the arctic seafloor, are currently destabilizing and releasing methane. So, lessons from Titan can provide important insights into processes happening on Earth."

The observed topography on Titan aligns with the study's findings. The methane clathrate crust indicates a warm interior, challenging prior assumptions of Titan's ice shell as cold, rigid, and inactive.

"Methane clathrate is stronger and more insulating than regular water ice," Schurmeier added. "A clathrate crust insulates Titan's interior, makes the water ice shell very warm and ductile, and implies that Titan's ice shell is or was slowly convecting."

Schurmeier also highlighted potential implications for astrobiology: "If life exists in Titan's ocean under the thick ice shell, any signs of life (biomarkers) would need to be transported up Titan's ice shell to where we could more easily access or view them with future missions. This is more likely to occur if Titan's ice shell is warm and convecting."

The upcoming NASA Dragonfly mission, set for a 2028 launch and 2034 arrival, will give researchers a closer look at Titan's surface, particularly Selk Crater, potentially advancing understanding of Titan's unique icy landscape.

Research Report:Rapid Impact Crater Relaxation Caused by an Insulating Methane Clathrate Crust on Titan