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Difficulty: HardIdentifying Hypotheses and Beliefs

Titan, Saturn's largest moon, has liquid methane (CH4CH_4) and ethane (C2H6C_2H_6) lakes on its surface. Since atmospheric methane is continuously destroyed by solar photolysis, it must be replenished from the moon's interior to maintain these lakes. Two models are proposed to explain this replenishment mechanism.

Model 1 (Clathrate Outgassing)
Titan's methane is stored in the crust within methane clathrate hydrates (water ice cages trapping methane molecules). Thermal anomalies caused by episodic runaway convection in Titan's rocky core warm the ice crust. This warming destabilizes the clathrate hydrates, releasing methane gas that rises through fractures to the surface and atmosphere. This process occurs in discrete outgassing events every few hundred million years, meaning lake levels fluctuate significantly over geologic time.

Model 2 (Cryovolcanic Eruptions)
Titan's interior contains a deep liquid water-ammonia ocean beneath a convective ice shell. Methane is dissolved directly in this sub-surface ocean. When pressure builds due to partial freezing of the ocean, cryovolcanic plumes of liquid water, ammonia, and dissolved methane erupt onto the surface. This cryovolcanism is a continuous process driven by tidal heating from Saturn, ensuring a steady, constant supply of methane to the surface lakes and atmosphere.

Which of the following beliefs is held by the proponents of Model 1 but NOT by the proponents of Model 2 regarding the replenishment of Titan's methane lakes?

  1. Methane replenishment occurs in discrete, episodic events driven by thermal convection in the rocky core.Answer
  2. B
    Methane is supplied to the surface continuously as a result of gravitational tidal heating from Saturn.
  3. C
    Methane is stored inside water ice cages in the crust and is released continuously to maintain stable lake levels.
  4. D
    Methane is dissolved in a sub-surface water-ammonia ocean and is released during runaway core heating events.

Answer

Methane replenishment occurs in discrete, episodic events driven by thermal convection in the rocky core.
The correct answer accurately describes the core mechanism of Model 1, which states that methane is stored in clathrates and released in discrete outgassing events driven by core convection. This contrasts directly with Model 2, which claims that methane is dissolved in a sub-surface ocean and released continuously via tidal-heating-driven cryovolcanism.

Step-by-Step Solution

1
Analyze the description of Model 1's replenishment mechanism.
Model 1 describes methane storage in clathrates, released via episodic outgassing events driven by runaway convection in the rocky core.
This establishes the core claims of Model 1.
2
Analyze the description of Model 2's replenishment mechanism.
Model 2 describes methane dissolved in a sub-surface water-ammonia ocean, released via continuous cryovolcanic eruptions driven by tidal heating.
This establishes the core claims of Model 2.
3
Compare the claims to find a belief unique to Model 1.
The claim that replenishment occurs in discrete, episodic events driven by core convection is unique to Model 1.
This matches the question's requirement to find a belief held by Model 1 but not Model 2.

Key Concept

Identifying Hypotheses and Beliefs
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Topics

Identifying Hypotheses and Beliefs

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