### Heat Source of Enceladus Scientists debate the primary heat source maintaining the sub… — ACT

### Heat Source of Enceladus

Scientists debate the primary heat source maintaining the subsurface liquid water ocean on Saturn's moon, Enceladus.

Hypothesis 1
The liquid ocean is maintained primarily by tidal heating. Gravitational interactions with Saturn and other moons deform Enceladus, generating frictional heat within its silicate core and ice shell. Frictional heating in the core is highly localized and can produce temperatures exceeding $100^\circ\text{C}$ .

Hypothesis 2
The liquid ocean is maintained primarily by radiogenic heating. The decay of radioactive isotopes (such as Uranium-235 and Potassium-40) in the moon's rocky core releases steady, uniform thermal energy. This decay is estimated to produce maximum core-mantle boundary temperatures of approximately $30^\circ\text{C}$ .

New Evidence
Analysis of the water plumes erupting from Enceladus's south polar region reveals the presence of silica nanoparticles ( $SiO_2$ ). Laboratory experiments show that these nanoparticles can only form when alkaline water containing dissolved silica is heated to at least $90^\circ\text{C}$ at the seafloor.

Which of the following statements best describes how this new evidence affects Hypotheses 1 and 2?

It weakens Hypothesis 2 because radiogenic heating cannot generate the minimum temperature required to form the silica nanoparticles, and it supports Hypothesis 1 because tidal heating can produce these temperatures.Answer
B
It supports Hypothesis 2 because radiogenic decay generates the steady, uniform temperatures required to synthesize silica nanoparticles, and it weakens Hypothesis 1.
C
It weakens both Hypothesis 1 and Hypothesis 2 because the presence of silica nanoparticles implies the ocean is composed of liquid methane rather than water.
D
It has no effect on either Hypothesis 1 or Hypothesis 2 because silica nanoparticles can only form at temperatures below $30^\circ\text{C}$ , which both hypotheses can easily produce.

Answer

The statement indicating that the evidence weakens Hypothesis 2 because radiogenic heating cannot generate the minimum temperature required to form the silica nanoparticles, and supports Hypothesis 1 because tidal heating can produce these temperatures.

The new evidence establishes a minimum temperature threshold of

90^\circ\text{C}

for silica nanoparticle formation. This weakens Hypothesis 2, which states radiogenic heating only reaches

30^\circ\text{C}

. It supports Hypothesis 1, which allows for temperatures above

100^\circ\text{C}

Step-by-Step Solution

Identify the temperature constraint introduced by the new evidence.

Silica nanoparticles require seafloor temperatures of at least

90^\circ\text{C}

to form in alkaline water.

To evaluate how the evidence impacts the hypotheses, we must first establish the physical conditions the evidence demands.

Compare this temperature constraint with the predictions of Hypothesis 2 (radiogenic heating).

Hypothesis 2 predicts a maximum core-mantle boundary temperature of

30^\circ\text{C}

, which is far below the required

90^\circ\text{C}

If a hypothesis cannot account for the physical conditions demonstrated by new evidence, that evidence weakens the hypothesis.

Compare the temperature constraint with the predictions of Hypothesis 1 (tidal heating).

Hypothesis 1 predicts localized core temperatures exceeding

100^\circ\text{C}

, which is sufficient to form the nanoparticles at

90^\circ\text{C}

If a hypothesis predicts conditions that can accommodate the new findings, the evidence supports that hypothesis.

Key Concept

Evaluating the impact of new scientific evidence on conflicting hypotheses

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