An international team of planetary scientists may have solved the mystery of why the atmosphere of Saturn's moon, Titan, is rich in methane.
Methane, which on Titan plays a role similar to water on Earth, is locked in a methane-rich water ice that forms a crust above an ocean of liquid water mixed with ammonia, the scientists say. Major episodes of outgassing pumped methane into Titan's mostly nitrogen atmosphere three times during the moon's evolutionary history, they discovered.
The first episode of methane gas release happened after Titan formed its dense rock core and water mantle beneath an ice crust, said UA planetary sciences Professor Jonathan Lunine, an interdisciplinary scientist for the Huygens probe.
Ammonia acting as an antifreeze, heat leftover from formation, and heat from radioactive elements aided the release of methane during the first billion years, or possibly just a few hundred million years, in Titan's history. Much of the methane in this first release might have been reabsorbed into Titan's interior. But whatever methane was left in the atmosphere was photochemically destroyed in the first billion years, Lunine said.
The second methane-release episode around two billion years ago is even more interesting, Lunine said. That's when convection began within Titan's silicate core. "The core, made of rock, continued to heat up because it contains natural radioactive elements like uranium, potassium and thorium. On Earth, these elements are concentrated in the crust, but on Titan, they'd be deep down in the rock. So the core gets hotter and hotter, until finally it's soft enough for convection to start."
Convection is the mechanical turnover of material to remove heat. The second event of around two billion years ago injected a burst of convection heat into Titan's overlying mantle, causing the ice crust to thin and methane to outgas through ice to the surface.
The latest methane-release episode began around 500 million years ago. It's the result of the planet cooling by convection in Titan's solid ice crust.
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A mite bit disappointing if true.