Logical Reasoning

PT13 · S4 · Q5 Planetary bodies differ from one another

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Planetary bodies differ from one another in their composition, but most of those in the Solar System have solid surfaces.

Premise

If a planetary body with a solid surface does not have a core that generates enough heat for volcanic action, its surface will not be renewed for millions of years.

Premise

Any solid-surface body whose surface is not renewed for millions of years becomes heavily pockmarked by meteorite craters.

Premise

Some old planetary bodies — including Europa, a very cold moon of Jupiter — have solid icy surfaces with very few meteorite craters.

Anticipate

Chain the conditionals: no volcanic-heat core -> surface not renewed -> heavily pockmarked. Contrapositive: not heavily pockmarked -> surface was renewed -> core does generate enough heat for volcanic action. Europa is old, cold, has a solid surface, and is not heavily pockmarked. So Europa's core must generate enough heat for volcanic action.

Goal

Find the answer that captures this contrapositive — at least some very cold body has a volcanically active core.

If the claims above are true, which one of the following must, on the basis of them, be true?

The Earth’s Moon does not
Out of Scope
The stimulus uses the Moon as a generic example of what a heavily pockmarked surface looks like, but it never says the Moon does or doesn't have ice. We can't infer this from the stimulus.
4% picked this
If a planetary body does
Reversal
The stimulus says: no volcanic core -> not renewed -> pockmarked. The contrapositive (what we can derive) is: not pockmarked -> volcanic core. This answer takes the contrapositive of the second link only — not pockmarked -> core doesn't generate volcanic heat — which is actually a flat reversal of the contrapositive's direction. The stimulus does not let us conclude that absence of pockmarking means absence of volcanic activity.
16% picked this
Some planetary bodies whose cores
Unsupported
The stimulus tells us nothing about planetary bodies that do have volcanic cores but lack solid icy surfaces. This claim about a category — bodies with volcanic cores that don't have icy surfaces — has no support either way from the stimulus.
16% picked this
Some of Jupiter’s moons are
Unsupported
The stimulus mentions Europa, one of Jupiter's moons. From that, we can't conclude anything about Jupiter's other moons. Some of them might be heavily pockmarked, but the stimulus gives us no information about them.
4% picked this
Correct
Some very cold planetary bodies
Why this is right
This is the contrapositive at work. Europa is described as very cold, solid-surfaced, and not heavily pockmarked. Working backward through the chain: not pockmarked -> surface was renewed within millions of years -> core generates enough heat for volcanic action. So Europa is a very cold body with a volcanic-heat core, which means at least one very cold body has such a core. That's exactly what (E) claims.
Skill tested: Must be True · how this choice captures the argument's function is the move to repeat next time.
60% picked this

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