Soru

### Titan's Atmospheric Methane

Titan, Saturn's largest moon, has a thick atmosphere rich in methane ($CH_4$). Because solar ultraviolet radiation continuously breaks down atmospheric $CH_4$ through photochemical reactions, Titan's atmospheric $CH_4$ must be replenished from an internal reservoir to maintain its observed levels. Two scientists propose differing mechanisms for this replenishment.

Scientist 1
Titan's $CH_4$ is stored as methane clathrate hydrates—compounds in which $CH_4$ molecules are trapped inside cages of water ice—within its outer icy crust. These clathrates were incorporated into Titan during its accretion from the cold solar nebula. Periodically, thermal plumes rising from Titan's rocky core warm the base of the crust, causing the clathrates to dissociate (break apart) and release gaseous $CH_4$. This gas then migrates upward through fractures in the ice shell and enters the atmosphere.

Scientist 2
Titan's $CH_4$ is continuously produced by serpentinization within its rocky core. Liquid water from Titan's subsurface ocean circulates through the olivine-rich rocky core at high temperatures (exceeding $150^\circ\text{C}$). The chemical reaction between water and olivine produces hydrogen gas ($H_2$), which then reacts with carbon dioxide ($CO_2$) via the Sabatier reaction to synthesize $CH_4$. This newly formed $CH_4$ rises through the subsurface ocean and the overlying ice shell to replenish the atmosphere.

Scientist 2's hypothesis relies on which of the following underlying assumptions regarding Titan's internal structure?