ConceptChecks
ConceptCheck 14-1: The trajectory of Uranus did not show slow changes in speed predicted by its orbit around the Sun. Instead, Uranus deviated by slightly speeding up and slowing down, and this could be attributed to a new planet at just the right location.
ConceptCheck 14-2: Methane in Uranus’s atmosphere absorbs the Sun’s longer wavelengths of light, so if it were absent, Uranus would have more reds and, as a result, appear more yellow-white, like Saturn.
ConceptCheck 14-3: It is thought that Neptune is still contracting, which converts gravitational energy into thermal energy to power its atmosphere.
ConceptCheck 14-4: At Neptune’s present distance, there would not have been enough matter to form such a large planet. Furthermore, even if there were more matter, Neptune has a higher proportion of heavy elements than expected in the outer reaches of the solar system.
ConceptCheck 14-5: Ammonia dissolved in water under high pressure loses electrons, which become free to move, and this makes the fluid electrically conductive.
ConceptCheck 14-6: Due to radiation darkening, Uranian rings are black as coal, unlike Saturn’s icy light-reflecting rings. Uranus’s rings are also very narrow, at about 10 km wide, compared to rings on Saturn that can be over 1000 times wider.
ConceptCheck 14-7: The orbits of some moons were seen to change between observations made in 1994 and 2005. Based on the degree of observed change, it might only have taken a few hundred million years before these moons would have collided, so they might have been acquired somewhat recently.
ConceptCheck 14-8: Geyserlike plumes observed by Voyager 2 showed streaking, indicating that they were carried downwind by a thin atmosphere.
ConceptCheck 14-9: Pluto’s gravity is too weak to clear its neighborhood of nearby planetesimals in the Kuiper belt. According to new classifications adopted in 2006—that a planet must clear its neighborhood—this makes Pluto a dwarf planet instead of a planet.
ConceptCheck 14-10: Pluto is much smaller than any planet, and has a much higher fraction of water-ice.