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Difficulty: MediumAssessing Model Support and Contradiction

### Enceladus Plume Sources

Scientists are investigating the source of the plumes of gas and ice grains erupting from the south polar region of Saturn's moon, Enceladus. Two models have been proposed:

Model 1 (Subsurface Ocean Model)
The plumes originate from a global liquid water ocean situated between Enceladus's icy outer shell and its active, rocky silicate core. Tidal forces flex the core, causing hydrothermal activity (temperatures >90∘C> 90^\circ\text{C}). This water-rock interaction dissolves silica (SiO2SiO_2) and produces molecular hydrogen (H2H_2) via chemical reactions. Upwelling currents transport the water, dissolved silica, and dissolved gases to the surface, where they erupt through fractures in the ice shell as gas and ice grains containing silica nanoparticles.

Model 2 (Clathrate Hydrate Model)
The plumes originate entirely within the shallow, icy outer shell. The shell contains clathrate hydrates—structures of water ice that cage gas molecules (primarily CH4CH_4 and CO2CO_2) under high pressure. Tidal forces cause friction along fractures in the ice, heating the surrounding ice to temperatures well below 0∘C0^\circ\text{C}. This localized heating causes the clathrates to decompose, releasing the trapped gases, which then escape into space. Because this process occurs entirely within the cold ice shell, there is no high-temperature water-rock interaction at the core to produce silica nanoparticles or free H2H_2.

A spacecraft analyzes the composition of the ice grains ejected from the Enceladus plumes. The analysis detects significant amounts of silica nanoparticles (SiO2SiO_2) and molecular hydrogen (H2H_2) gas.

Based on the models, does the detection of silica nanoparticles and molecular hydrogen in the plume ice grains support Model 1, Model 2, or both?

  1. It supports Model 1 only, because the detection of these substances indicates high-temperature water-rock interactions at the core, which is unique to Model 1.Answer
  2. B
    It supports Model 2 only, because clathrate hydrate decomposition in the icy outer shell is the primary mechanism for generating silica nanoparticles and molecular hydrogen.
  3. C
    It supports both Model 1 and Model 2, because both models rely on active hydrothermal vents at the core boundary to release chemical compounds into the plumes.
  4. D
    It contradicts both Model 1 and Model 2, because neither model accounts for the presence of gaseous compounds or solid particles being carried through the ice shell.

Answer

It supports Model 1 only, because the detection of these substances indicates high-temperature water-rock interactions at the core, which is unique to Model 1.
The finding supports the subsurface ocean model only. According to the description of the subsurface ocean model, hydrothermal activity at the core-ocean boundary dissolves silica and produces molecular hydrogen (H2H_2). These are then carried to the surface and erupted in the plumes. In contrast, the clathrate hydrate model takes place entirely within the cold ice shell and does not feature high-temperature water-rock interaction at the core, meaning it cannot produce these substances. Therefore, the finding supports the subsurface ocean model but not the clathrate hydrate model.

Step-by-Step Solution

1
Identify the key components of the new findings.
The new findings show the presence of silica nanoparticles (SiO2SiO_2) and molecular hydrogen (H2H_2) gas in the plume ice grains.
This establishes what evidence needs to be evaluated against the models.
2
Compare the findings with the claims of Model 1.
Model 1 states that high-temperature water-rock interactions at the core-ocean boundary dissolve silica (SiO2SiO_2) and produce molecular hydrogen (H2H_2), which are then carried up and ejected in the plumes.
This determines if Model 1 supports or contradicts the findings.
3
Compare the findings with the claims of Model 2.
Model 2 states that the process occurs entirely in the cold ice shell without high-temperature water-rock interaction at the core, meaning there is no source to produce silica nanoparticles or free H2H_2.
This determines if Model 2 supports or contradicts the findings.
4
Synthesize the evaluation.
Since the evidence is predicted by Model 1 but cannot be produced under Model 2, the findings support Model 1 only.
This leads to the correct final choice selection.

Key Concept

Assessing Model Support and Contradiction
Estimated Time:1m 30s
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Assessing Model Support and Contradiction

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