Explanation
Correct answer: A.
Choice A is the best answer because it reflects how Tsai et al. would most likely respond to Madhusudhan et al.’s identification of K2-18 b as a hycean candidate. Text 1 establishes that the habitable zone (HZ) for potential hycean planets, which are typified by abundant liquid water and hydrogen-rich atmospheres, represents “the distance from a star that allows a planet to retain liquid water on its surface” and is estimated to begin at about 1 astronomical unit (AU). Based on this characterization of the HZ, Madhusudhan et al. identified K2-18 b as a hycean candidate whose location falls on the “inner edge” of the HZ—implying that its distance from its star is about 1 AU. However, Text 2 presents Tsai et al.’s claim that the same hydrogen-rich atmospheres that typify K2-18 b and other hycean candidates “admit wavelengths of light that cause elevated surface temperatures and increased water evaporation,” phenomena that would be exacerbated by proximity to their host stars. Tsai et al. instead placed the inner edge of the HZ “as far out as 3.85 AU,” implying that hycean candidates at lesser distances from their stars would be unlikely to maintain liquid oceans because of elevated surface temperatures and subsequent water evaporation. According to Tsai et al.’s HZ estimate, K2-18 b—at roughly 1 AU—would be too close to its star to retain liquid water. Therefore, based on the details in the texts, Tsai et al. would most likely respond that the very atmospheric composition that defines K2-18 b as a hycean candidate suggests that it is unlikely to harbor liquid water on its surface.
Why the other choices are wrong
Choice B
Choice B is incorrect. In contrast to the suggestion that Madhusudhan et al.’s estimates of the surface temperature of hycean candidates are “likely too high,” Tsai et al.’s findings suggest the opposite: earlier assessments of the HZ didn’t fully account for the warming effect of wavelengths of light admitted by these planets’ hydrogen-rich atmospheres, which is why Tsai et al. placed the edge of the HZ farther out. The information in Text 2 therefore suggests that Tsai et al. would view Madhusudhan et al.’s temperature estimates as too low rather than as too high.
Choice C
Choice C is incorrect because neither text discusses other types of planets with hydrogen-rich atmospheres or compares them to hycean candidates. It therefore doesn’t follow from the information in the texts that Tsai et al. would observe that most other hydrogen-rich planets are likely within the HZ. Text 2 only indicates that the HZ for hycean candidates begins at about 3.85 AU and that K2-18 b therefore isn’t likely to be within the HZ, not that other planets with hydrogen-rich atmospheres are mostly located within the HZ.
Choice D
Choice D is incorrect because it mischaracterizes Tsai et al.’s findings. Rather than indicating that K2-18 b and other hycean candidates are “too far from the stars they orbit,” Tsai et al.’s findings suggest the opposite problem. Because these planets’ hydrogen-rich atmospheres admit wavelengths of light that cause elevated temperatures and water evaporation at distances of less than 3.85 AU, Tsai et al. would be more likely to argue that K2-18 b (at a distance of about 1 AU) and planets like it are too close to their stars, not too far from them. Moreover, Text 2 doesn’t suggest anything about hycean candidates more generally being unable to support life, only that hycean candidates at distances less than 3.85 AU from their stars, like K2-18 b, likely don’t have the liquid water needed to sustain life. Presumably, hycean candidates that are within the HZ described by Tsai et al. could harbor liquid oceans necessary for supporting life.