UH Manoa: New Study Shows Methane-Rich Crust on Titan May Hold Clues to Life: Maui Now

Saturn’s largest moon, Titan, is the only known place other than Earth to have an atmosphere and liquids in the form of rivers, lakes and seas on its surface. Due to its extremely low temperature, Titan’s liquids are composed of hydrocarbons such as methane and ethane, and its surface is made of solid water ice.

New researchled by planetary scientists at the University of Hawaii at Manoa, found that methane can also be trapped within the ice, forming a distinct crust up to six miles thick that heats the underlying icy shell and may also account for the methane-rich atmosphere.

Small impact craters lead to crustal hypothesis

The research team, led by postdoctoral fellow Lauren Schurmeier, includes Gwendolyn Brower, a doctoral student, and Sarah Fagents, associate director and researcher at the Hawaii Institute of Geophysics and Planetary Sciences in the School of Ocean and Earth Sciences and Technology at Manoa. Titan’s impact craters were hundreds of meters smaller than expected, according to NASA. Surprisingly, despite the fact that it is larger than Earth’s Moon, which has more million cratersOnly 90 craters have been discovered on Titan.

“This was very surprising because based on other satellites, we would expect to see many more impact craters on the surface and craters that are much deeper than what we see on Titan,” Schurmeier said. “We realized that something unique to Titan is causing it to become smaller and disappear relatively quickly.”

The researchers tested, using a computer model, how Titan’s topography might relax or recover after an impact if the icy shell were covered with a layer of insulating methane clathrate ice, a kind of solid water ice with methane gas trapped in a crystalline structure. Because the original shape of Titan’s craters is unknown, the researchers modeled and compared two likely initial depths based on similarly sized craters on the icy moon.

“Using this modeling approach, we were able to limit the thickness of the methane clathrate crust to five to ten kilometers (about three to six miles) because simulations using this thickness produced crater depths that best matched the observed craters,” Schurmeier said. “The methane clathrate crust heats Titan’s interior and causes remarkably rapid topographic relaxation, leading to shallowing of craters at rates similar to those of fast-moving warm glaciers on Earth.”

Methane-rich atmosphere

Estimating the thickness of the methane clathrate crust is important because it could explain the origin of Titan’s methane-rich atmosphere and help researchers understand Titan’s carbon cycle, liquid methane-based “hydrological cycle” and climate change.

“Titan is a natural laboratory for studying how the greenhouse gas methane heats up and circulates in the atmosphere,” Schurmeier said. “Earth methane clathrate hydrates, found in Siberian permafrost and beneath the Arctic seafloor, are currently destabilizing and releasing methane. Thus, lessons from Titan can provide important information about the processes occurring on Earth.”

Titan structure

Titan’s topography makes sense in light of these new discoveries. And limiting the thickness of the methane clathrate ice crust indicates that Titan’s interior is likely warm, rather than cold, rigid and inactive, as previously thought.

“Methane clathrate is more durable and insulating than regular water ice,” Schurmeier said. “The clathrate crust insulates Titan’s interior, making the water ice shell very warm and plastic, meaning Titan’s ice shell is or was in the process of slow convection.”

“If life exists in Titan’s ocean beneath a thick icy shell, any signs of life (biomarkers) would need to be transported up Titan’s icy shell to where we can more easily access them or see them on future missions,” Schurmeier added. “This is more likely if Titan’s icy shell is warm and convective.”

With NASA’s Dragonfly mission to Titan scheduled for July 2028 and arriving in 2034, researchers will have the opportunity to make close observations of this moon and further explore the icy surface, including Selk Crater.