Astronomers debate the origin of water on the Moon. Three viewpoints are proposed: **Viewp… — ACT

Astronomers debate the origin of water on the Moon. Three viewpoints are proposed:

Viewpoint 1 (Asteroid Delivery): Water was delivered to the Moon post-formation via impacts from carbonaceous chondrite asteroids. This water has a high deuterium-to-hydrogen ( $D/H$ ) ratio of approximately $1.5 \times 10^{-4}$ .

Viewpoint 2 (Earth Mantle Heritage): The Moon inherited its water directly from Earth’s mantle during the giant impact that formed the Moon. This water has a low $D/H$ ratio of approximately $0.3 \times 10^{-4}$ and is locked deep within the lunar mantle.

Viewpoint 3 (Solar Wind Implantation): Water ( $H_2O$ ) and hydroxyl ( $OH$ ) are continuously produced on the surface when solar wind protons ( $H^+$ ) impact oxygen-rich minerals in the lunar regolith (soil). This process only affects the exposed outermost layer of the soil.

Match each of the following new findings to the viewpoint that it directly supports.

Deep lunar mantle minerals contain water with a $D/H$ ratio of $0.3 \times 10^{-4}$ .Supports Viewpoint 2 (Earth Mantle Heritage)
Water ice deposits in polar craters show a $D/H$ ratio of $1.5 \times 10^{-4}$ .Supports Viewpoint 1 (Asteroid Delivery)
Hydroxyl groups are detected only in the top millimeters of lunar regolith exposed to solar radiation.Supports Viewpoint 3 (Solar Wind Implantation)

Answer

The correct pairings are: 'Deep lunar mantle minerals contain water with a D/H ratio of 0.3 x 10^-4' matches with 'Supports Viewpoint 2 (Earth Mantle Heritage)'; 'Water ice deposits in polar craters show a D/H ratio of 1.5 x 10^-4' matches with 'Supports Viewpoint 1 (Asteroid Delivery)'; and 'Hydroxyl groups are detected only in the top millimeters of lunar regolith exposed to solar radiation' matches with 'Supports Viewpoint 3 (Solar Wind Implantation)'.

The first finding of deep mantle water with a low

D/H

ratio (

0.3 \times 10^{-4}

) matches Viewpoint 2 (Earth Mantle Heritage), which states that the Moon inherited water from Earth's mantle with this low ratio. The second finding of polar crater ice with a high

D/H

ratio (

1.5 \times 10^{-4}

) matches Viewpoint 1 (Asteroid Delivery), which predicts a high ratio from carbonaceous chondrites. The third finding of shallow regolith hydroxyl groups matches Viewpoint 3 (Solar Wind Implantation), which specifies surface-only interactions driven by solar wind protons.

Step-by-Step Solution

Analyze the first finding concerning deep lunar mantle water with a

D/H

ratio of

0.3 \times 10^{-4}

This matches Viewpoint 2, which states that deep mantle water has a low

D/H

ratio of

0.3 \times 10^{-4}

inherited from Earth.

Aligning deep mantle signature with the specific Earth mantle heritage model.

Analyze the second finding concerning polar crater ice with a

D/H

ratio of

1.5 \times 10^{-4}

This matches Viewpoint 1, which states that asteroid-delivered water has a high

D/H

ratio of

1.5 \times 10^{-4}

Aligning surface ice signatures with the external asteroid delivery model.

Analyze the third finding concerning hydroxyl groups in the top millimeters of regolith.

This matches Viewpoint 3, which describes surface solar wind protons interacting only with the outermost layer of soil.

Aligning depth and exposure constraints with the solar wind model.

Key Concept

Aligning experimental data and observations with conflicting scientific hypotheses based on their specific predictions.

Estimated Time:1m 30s

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