Question 90·Hard·Rhetorical Synthesis
While researching a topic, a student has taken the following notes:
- In the transit method, an exoplanet passes in front of its star and causes a small, recurring dip in the star's brightness.
- The size of that dip helps astronomers estimate the exoplanet's radius.
- In the radial-velocity method, an orbiting exoplanet makes its star wobble slightly, shifting the star's spectral lines.
- Those spectral shifts help astronomers estimate the exoplanet's mass.
- When the same exoplanet is observed with both methods, astronomers can combine its radius and mass to calculate its average density.
- Average density can suggest whether an exoplanet is mostly rocky, icy, or gaseous.
The student wants to explain why astronomers especially value exoplanets that can be studied with both the transit and radial-velocity methods. Which choice most effectively uses relevant information from the notes to accomplish this goal?
For rhetorical synthesis questions, identify the exact task first. Here, the goal is not just to describe the two methods separately but to explain why astronomers especially value planets observed with both. The best answer should synthesize the notes into a cause-and-effect chain: transit gives radius, radial velocity gives mass, and together those measurements allow density-based inferences about composition. Eliminate choices that add unsupported outcomes, swap details, or shift to a different scientific question.
Hints
Focus on the stated goal
The prompt asks why astronomers especially value planets studied with both methods. So the best answer must explain what extra insight comes from combining the methods, not just restate what each one does on its own.
Match each method to the right measurement
According to the notes, the transit method helps estimate radius, while the radial-velocity method helps estimate mass. Any choice that swaps those two is wrong.
Look for the combined payoff
The notes say that when both methods are used on the same planet, astronomers can combine radius and mass to calculate average density. That density then suggests whether the planet is mostly rocky, icy, or gaseous.
Watch for tempting extra claims
Hard rhetorical synthesis questions often include choices that sound scientific but go beyond the notes. Be careful with claims about atmospheres, distance from the star, or any other result the notes never mention.
Step-by-step Explanation
Identify what the student wants to explain
The student wants to explain why exoplanets observed with both the transit and radial-velocity methods are especially valuable. So the correct answer must show the advantage of combining the two methods.
Pull the key detail from the transit notes
The notes say that in the transit method, a planet crossing in front of its star causes a recurring dip in brightness, and the size of that dip helps astronomers estimate the planet's radius.
Pull the key detail from the radial-velocity notes
The notes say that in the radial-velocity method, the planet makes the star wobble, shifting the star's spectral lines, and those shifts help astronomers estimate the planet's mass.
Choose the answer that uses both details correctly
The correct choice is the only one that puts the notes together accurately: if astronomers know a planet's radius and mass, they can calculate its average density, which can suggest whether the planet is mostly rocky, icy, or gaseous. The other choices either add unsupported information, substitute the wrong scientific result, or reverse which method gives which measurement.