Logical Reasoning

PT7 · S1 · Q16 Comets do not give off

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Comets do not give off their own light but reflect light from other sources, such as the Sun.

Setup

Comets reflect light, not generate it. Scientists estimate comet mass by brightness — more reflected light means more mass. But Halley's comet has been found to reflect 60 times less light per unit of mass than scientists previously thought.

Evaluate

If Halley's comet reflects 60x less light per unit of mass than thought, then for any given observed brightness, the actual mass must be much larger than the prior estimate suggested. The previous estimates — based on the wrong reflectivity assumption — were therefore too low: they were treating each unit of brightness as representing too little mass.

Goal

Find the answer that follows directly: previous mass estimates of Halley's based on its brightness were too low.

16.

The statements above, if true, give the most support to which one of the following?

  1. Some comets are composed of

    Unsupported

    The stimulus only tells us about Halley's reflectivity vs. what was previously thought. It doesn't establish anything about what other comets' material reflects, or compare Halley's to other comets. There's no support for "some comets reflect 60 times more per unit of mass."

    4% picked this

  2. Correct

    Previous estimates of the mass

    Why this is right

    This is what follows. Previous estimates were based on brightness, using a reflectivity assumption that turns out to have been 60x too high. So for the brightness observed, the previously inferred mass was too low — Halley's actual mass (per the new reflectivity figure) is much larger than the old estimate said.

    Skill tested: Most Supported · how this choice captures the argument's function is the move to repeat next time.

    44% picked this

  3. The total amount of light

    Unsupported

    The stimulus says scientists were wrong about the comet's reflectivity per unit of mass — not about the total amount of light reflected from the comet. The total light reflected hasn't changed; what's changed is the inferred relationship between that light and the comet's mass.

    36% picked this

  4. The reflective properties of the

    Unsupported

    The stimulus tells us about Halley's composition specifically, not about variation across comets. We have no information about how reflective different comets' materials are relative to each other.

    9% picked this

  5. Scientists need more information before

    Unsupported

    This is a recommendation about future research, not something the stimulus supports. With the new reflectivity figure, scientists can revise their estimate using the same brightness data — they don't obviously need more information to make a better estimate. The stimulus gives no basis for saying the existing data is insufficient.

    6% picked this

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