NASA’s Cassini probe has detected an unusual wobble in the rotation of Mimas, Saturn’s smallest moon. Using a computer model to study Mimas’s gravitational interactions with Saturn and tidal forces, geophysicist Alyssa Rhoden and colleagues have proposed that this wobble could be due to a liquid ocean moving beneath the moon’s icy surface. The researchers believe other moons should be examined to see if they too might have oceans hidden beneath their surfaces.
","stem_html":"Which choice best states the main idea of the text?
","rationale_html":"Choice D is the best answer. The study isn’t definitive, but it says that Mimas’s wobbly rotation could be explained by the hidden ocean.
Choice A is incorrect. This choice goes too far beyond the information in the text. Rhoden’s team proposed that one moon of Saturn could have a liquid ocean beneath its surface, and that other moons should also be examined, but no one has confirmed anything. Choice B is incorrect. This choice conflicts with the text. Research has identified at least one sign—the unusual wobble in Mimas’s rotation—that might be due to a hidden ocean beneath its surface. Choice C is incorrect. This choice doesn’t reflect the text. The computer model studies “gravitational interactions,” which seem to account for the wobbly rotation of Mimas.
","correct_answer":["D"],"has_media":false,"has_mathml":false,"has_table":false,"source_created_at":"2023-08-02T20:25:59.359000+00:00","source_updated_at":"2023-08-02T20:25:59.359000+00:00","options":[{"label":"A","content_html":"Rhoden and colleagues were the first to confirm that several of Saturn’s moons contain hidden oceans.
","ord":0},{"label":"B","content_html":"Research has failed to identify signs that there is an ocean hidden beneath the surface of Mimas.
","ord":1},{"label":"C","content_html":"Rhoden and colleagues created a new computer model that identifies moons with hidden oceans without needing to analyze the moons’ rotation.
","ord":2},{"label":"D","content_html":"Research has revealed that an oddity in the rotation of Mimas could be explained by an ocean hidden beneath its surface.
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