Titan is covered in an insulating crust rich in methane

Oct. 25 () –

Planetary scientists at the University of Hawaii at Manoa have revealed that Saturn’s largest moon, Titan, has a methane-rich insulating crust of up to almost 10 kilometers thick.

This layer warms the underlying ice sheet and may also explain Titan’s methane-rich atmosphere, the only known place other than Earth to have an atmosphere and liquids in the form of rivers, lakes and seas on its surface. These findings are published in The Planetary Science Journal.

Due to its extremely cold temperature, Titan’s liquids are made of hydrocarbons such as methane and ethane, and the surface is made of solid water ice.

The research team observed in NASA data that Titan’s impact craters are hundreds of meters shallower than expected and only 90 craters have been identified on this moon.

“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 see on Titan,” he said. in a statement research associate Lauren Schurmeier. “We realized that something unique to Titan must be causing them to become more superficial and disappear relatively quickly.”

To investigate what might be behind this mystery, the researchers tested in a computer model how Titan’s topography could relax or recover after an impact if the ice sheet were covered with a layer of insulating methane clathrate, a type of solid water ice with methane gas trapped within the crystalline structure.

Since the initial shape of Titan’s craters is unknown, the researchers modeled and compared two plausible initial depths, based on recent-looking craters of similar size on a similarly sized icy moon, Ganymede.

“Using this modeling approach, we were able to limit the thickness of the methane clathrate crust to 5 to 10 kilometers because simulations using that thickness produced crater depths that coincided better with the observed craters“Schurmeier said.

“The methane clathrate crust heats Titan’s interior and causes surprisingly rapid topographic relaxation, resulting in a flattening of the craters to a speed close to that of fast-moving warm glaciers on Earth.”

Calculating the thickness of the methane ice shell is important because it can explain the origin of Titan’s methane-rich atmosphere and helps researchers understand Titan’s carbon cycle, the “hydrological cycle” based on liquid methane and climate change.

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

The topography observed on Titan makes sense in light of these new findings. And the limitation of the thickness of the methane clathrate ice crust indicates that Titan’s interior is probably warm, not cold, rigid and inactive as previously thought.

“Methane clathrate is stronger and more insulating than normal water ice,” Schurmeier said. “A clathrate crust insulates Titan’s interior, makes the water ice shell very warm and ductile, and implies that Titan’s ice sheet is or was in slow convection.”

“If life exists in Titan’s ocean beneath the thick ice sheet, any signs of life (biomarkers) would have to be transported up Titan’s ice sheet to where we could access or see them more easily with future missions.” Schurmeier added. “This is more likely to occur if Titan’s ice sheet is warm and convecting.”

NASA’s Dragonfly mission to Titan, scheduled to launch in July 2028 and arrive in 2034, will allow researchers to make close observations of this moon and further investigate its icy surface, including a crater called Selk.