Two astrobiologists discuss the origin of methane (CH_4) plumes detected in the atmosphere… — ACT

Two astrobiologists discuss the origin of methane ( $CH_4$ ) plumes detected in the atmosphere of Saturn’s moon, Enceladus.

Astrobiologist 1
Methane in the plumes is biological, produced by methanogenic microorganisms in subsurface hydrothermal vents via the reaction:

CO_2 + 4H_2 \rightarrow CH_4 + 2H_2O

Because biological enzymes preferentially utilize the lighter carbon isotope (

^{12}C

) over the heavier isotope (

^{13}C

), metabolic reactions significantly enrich the methane in

^{12}C

. This results in a

^{12}C/^{13}C

ratio in the plumes that is much higher than the solar system's primordial carbon ratio of approximately

89

. Additionally, biological methanogenesis does not produce heavier, multi-carbon alkanes.

Astrobiologist 2
Methane in the plumes is abiotic, formed deep within the core of Enceladus through serpentinization (the reaction of water with olivine rocks) followed by Fischer-Tropsch-type ( $FTT$ ) synthesis. $FTT$ synthesis always produces methane alongside other small alkanes, specifically ethane ( $C_2H_6$ ) and propane ( $C_3H_8$ ). Because $FTT$ synthesis does not significantly fractionate carbon isotopes, the methane in the plumes will have a $^{12}C/^{13}C$ ratio that is nearly identical to the primordial baseline of $89$ .

Suppose a new probe measures a plume on Enceladus and detects $CH_4$ with a $^{12}C/^{13}C$ ratio of $108$ , but detects no measurable $C_2H_6$ or $C_3H_8$ . Based on the provided information, is the statement 'This discovery supports the model of Astrobiologist 2 and contradicts the model of Astrobiologist 1' true or false?

Answer: Answer

Answer

False

The correct answer is False because the high carbon isotope ratio of

108

matches the biological carbon fractionation predicted by Astrobiologist 1, and the absence of ethane and propane contradicts the mandatory alkane co-occurrence predicted by Astrobiologist 2. Therefore, the data actually supports Astrobiologist 1 and contradicts Astrobiologist 2.

Step-by-Step Solution

Analyze the properties of the newly discovered plume data.

The plume contains methane, has a

^{12}C/^{13}C

ratio of

108

, and contains no detectable ethane (

C_2H_6

) or propane (

C_3H_8

To identify the key variables needed to evaluate each viewpoint.

Compare the observed properties with the predictions of Astrobiologist 1.

Astrobiologist 1 predicts a

^{12}C/^{13}C

ratio significantly higher than

89

due to biological fractionation and does not predict the production of heavier alkanes. The observed ratio of

108

and the lack of ethane/propane support this model.

To determine whether the data aligns with the biological origin hypothesis.

Compare the observed properties with the predictions of Astrobiologist 2.

Astrobiologist 2 predicts a

^{12}C/^{13}C

ratio near

89

and requires the presence of ethane and propane. The observed ratio of

108

and the lack of these alkanes directly contradict this model.

To determine whether the data aligns with the abiotic origin hypothesis.

Evaluate the truth value of the target statement based on these alignments.

Since the data supports Astrobiologist 1 and contradicts Astrobiologist 2, the statement claiming the reverse is false.

To make the final assessment of the statement's validity.

Key Concept

Aligning experimental data and isotopic/chemical signatures with conflicting scientific viewpoints.

Question

Answer

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Key Concept

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