by Scientists have discovered that the icy shell of Saturn’s largest moon, Titan, could have an isolated, six-mile-thick (9.7-kilometer-thick) layer of methane ice beneath its surface. Ironically, this layer could make signs of life from Titan’s subsurface ocean easier to detect. And in the long term, the discovery could benefit the fight against man-made climate change on Earth.
Titan may be a moon, but it’s also more Earth-like than any other planet in the solar system. That’s because it is the only planet or moon in the solar system, apart from Earth, that has an atmosphere as well as liquid rivers, lakes and seas. However, due to Titan’s frigid temperatures, this fluid is composed of hydrocarbons such as methane and ethane. Yet Titan’s surface ice is indeed water.
The new results from a team of planetary scientists from the University of Hawaii at Mānoa revealed that methane gas may also be trapped in Titan’s ice shell, creating a distinct crust that could be up to six miles thick. This gas could warm the underlying ice shell and help molecules rise to Titan’s surface, some of which could indicate the presence of life. This warming may also help explain Titan’s methane-rich atmosphere.
“If life exists in Titan’s ocean beneath the thick ice layer, all signs of life, biomarkers, should be transported to Titan’s ice shell, where we can more easily reach or view them with future missions,” says research team leader and University of New York. Hawaiian scientist Lauren Schurmeier said in a statement. “This is more likely to happen if Titan’s ice shell is warm and connecting.”
The team was first alerted to the possible existence of this connecting layer of methane ice by the presence of shallow impact craters on Titan. Only 90 impact craters have been observed on the surface of Saturn’s moon, and these were confusing to observe because they should are hundreds of meters deeper than they actually are.
“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 said. “We realized that something unique about Titan must be causing them to become shallower and disappear relatively quickly.”
Exploring Titan’s shallow craters
To further investigate the mystery of Titans’ swallow impact craters, Schurmeier and colleagues turned to computer modeling. This allowed them to test how much the surface of Saturn’s largest moon would relax and bounce back after an asteroid impact if its icy shell were covered with an insulating layer of methane clathrate.
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Methane clathrate, or ‘methane hydrate’, is a solid in which a large amount of methane is trapped in the crystalline structure of water, creating a solid that resembles ice.
Considering similarly sized craters on an icy moon of Jupiter similar to Titan, Ganymede, the researchers were able to compare the possible depths of impact craters on Saturn’s moon.
“Using this modeling approach, we were able to constrain the thickness of the methane clathrate crust to five to ten kilometers [about three to six miles] because simulations with that thickness produced crater depths that best matched observed craters,” Schurmeier added. “The methane clathrate crust heats Titan’s interior and causes surprisingly rapid topographic relaxation, resulting in the crater shallowing at a rate is close to that of rapid craters. moving warm glaciers on Earth.”
The thickness of this icy methane shell is important because it could ultimately explain why Titan’s atmosphere is particularly rich in this hydrocarbon. It could also help scientists better understand Titan’s carbon cycle, its liquid methane-based ‘hydrological cycle’ and the changing climate of Saturn’s moon.
“Titan is a natural laboratory for studying how the greenhouse gas methane heats and circulates through the atmosphere,” Schurmeier explains. “Earth’s methane clathrate hydrates, found in the permafrost of Siberia and beneath the Arctic seafloor, are currently destabilizing and releasing methane.
“Lessons from Titan can thus provide important insights into processes taking place on Earth.”
The thickness of the methane clathrate crust, viewed in light of Titan’s topography, means that Saturn’s moon interior is likely warm and flexible rather than cold and stiff as once thought.
“Methane clathrate is stronger and better 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.”
And that convection means that biomarkers indicative of life could have been lifted from Titan’s subsurface ocean and brought to Titan’s outer icy shell, awaiting discovery.
This research could serve as a useful guide for NASA scientists planning to explore Titan using the upcoming Dragonfly spacecraft. Dragonfly will launch in 2028 and will hopefully reach the Saturn system in 2034 to conduct up-close observations of Titan’s icy surface.
The team’s research was published September 30 in The Planetary Science Journal.
Originally posted on Space.com.
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