Some astronomers searching for extraterrestrial life have proposed that atmospheric NH_3 (ammonia) can serve as a biosignature gas—an indication that a planet harbors life. Jingcheng Huang, Sara Seager, and colleagues evaluated this possibility, finding that on rocky planets, atmospheric NH_3 likely couldn’t reach detectably high levels in the absence of biological activity. But the team also found that on so-called mini-Neptunes—gas planets smaller than Neptune but with atmospheres similar to Neptune’s—atmospheric pressure and temperature can be high enough to produce atmospheric NH_3. Based on the text, Huang, Seager, and colleagues would most likely agree with which statement about atmospheric NH_3?
","rationale_html":"Choice C is the best answer because it states a conclusion the researchers likely agree with, given the details in the text. The text explains that a biosignature gas is a gas that can be used as an indicator that a planet harbors some form of life and some astronomers have proposed that NH₃ could serve as a biosignature gas. The researchers evaluating this claim found that the atmosphere of rocky planets would be unlikely to reach “detectably high levels” of NH₃ without biological activity, which would support the proposal of NH₃ serving as a biosignature gas. However, the text also states that mini-Neptune planets can produce NH₃ in the absence of biological activity. Thus, the text is structured to lead to the conclusion that detectable levels of NH₃ in the atmospheres of rocky planets could constitute a biosignature, but that is not the case for detectable levels of the gas in the atmospheres of mini-Neptune planets. Choice A is incorrect because the text indicates that biological activity likely accounts for detectable levels of NH₃ in the atmospheres of rocky planets but mini-Neptune planets can have detectable levels of NH₃ in their atmospheres in the absence of biological activity. Therefore, both rocky planets and mini- Neptune planets can have detectable levels of atmospheric NH₃. Choice B is incorrect because the text states that for NH₃ to reach detectable levels in the atmospheres of rocky planets likely means they harbor biological activity, meaning that rocky planets with detectable NH₃ usually harbor biological activity. However, that does not entail that every rocky planet with biological activity will have detectable levels of NH₃ in their atmospheres. Choice D is incorrect because the text claims only that some astronomers have proposed using NH₃ as a biosignature gas without mentioning a minimum concentration of atmospheric NH₃ that must be met for it to function as a biosignature gas.
","correct_answer":["C"],"has_media":false,"has_mathml":false,"has_table":false,"source_created_at":null,"source_updated_at":null,"options":[{"label":"A","content_html":"Its presence is more likely to indicate that a planet is a mini-Neptune than that the planet is a rocky planet that could support life.
","ord":0},{"label":"B","content_html":"Its absence from a planet that’s not a mini-Neptune indicates that the planet probably doesn’t have life.
","ord":1},{"label":"C","content_html":"It should be treated as a biosignature gas if detected in the atmosphere of a rocky planet but not if detected in the atmosphere of a mini-Neptune.
","ord":2},{"label":"D","content_html":"It doesn’t reliably reach high enough concentrations in the atmospheres of rocky planets or mini-Neptunes to be treated as a biosignature gas.
","ord":3}],"attribution":{"source_id":"cb_practice_pdf","source_name":"College Board full-length SAT practice tests (PDF)","rights_holder":"College Board","canonical_url":"https://satsuite.collegeboard.org/practice/practice-tests/paper","retrieved_from":"https://satsuite.collegeboard.org/practice/practice-tests/paper","attribution":"Full-length SAT practice tests 4–11 © College Board, published free at satsuite.collegeboard.org.","disclaimer":"Extracted from PDF layout: equations, figures and tables do not survive intact. Use the original PDFs for anything the text renders poorly. SAT® is a trademark registered by the College Board, which is not affiliated with and does not endorse this project.","license":"College Board copyright. Free to download; not licensed for redistribution.","redistributable":false,"item_count":905}}