Asteroid 6478 Gault has experienced intermittent mass loss since at least 2013, but in contrast to some other asteroids with repeated mass-loss episodes, 6478 Gault has not lost mass at its perihelion (the closest point of its orbit to the Sun), and thus the loss is not attributable to solar energy-driven ice vaporization. And as Jane X. Luu et al. point out, the singular nature of impact ejection makes it untenable as an account of multiple loss episodes of similar duration over several years. Instead, Luu et al. are likely correct that 6478 Gault is shedding mass due to rotational instability.
Which choice best describes the overall structure of the text?
Explanation
Context: This passage discusses asteroid 6478 Gault, which has experienced repeated mass-loss events since at least 2013. It rules out solar-driven ice vaporization, since Gault's mass loss doesn't occur at its perihelion, and it rules out impact ejection, since its singular nature could not explain multiple similar-duration loss episodes over several years. It concludes that Luu and colleagues are likely correct that rotational instability is the true cause. The question asks which choice best describes the structure of this passage.
Answer: C) It introduces a natural phenomenon, refutes two potential explanations for that phenomenon, and then presents a third explanation for that phenomenon that the author regards as plausible.
Why? The passage introduces Gault's mass loss, eliminates solar ice vaporization, eliminates impact ejection, and then endorses rotational instability as the explanation the author regards as plausible. Choice C matches this four-part structure.
Traps:
- A) "describes an astronomical finding, discusses competing theories about the finding..." → two theories are actively refuted before one is endorsed
- B) "presents a scientific observation, describes a contrast between that observation and similar phenomena..." → the contrast is between explanations, not phenomena
- D) "discusses a physical process, evaluates possible causes of that process, and concludes that none fully explains it" → rotational instability is endorsed as likely correct