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Lecture PowerPoint Chapter 13 Astronomy Today, 5th edition Chaisson McMillan © 2005 Pearson Prentice Hall This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials. Chapter 13 Uranus, Neptune, and Pluto Units of Chapter 13 The Discovery of Uranus The Discovery of Neptune Physical Properties of Uranus and Neptune The Atmospheres of Uranus and Neptune Magnetospheres and Internal Structure The Moon Systems of Uranus and Neptune The Rings of the Outermost Jovian Planets Units of Chapter 13, cont. The Discovery of Pluto Physical Properties of Pluto The Origin of Pluto Surface Detail on Planet Pluto 13.1 The Discovery of Uranus Discovered in 1781 by Herschel; first planet to be discovered in more than 2000 years Little detail can be seen from Earth; arrows point to three of Uranus’s moons: 13.2 The Discovery of Neptune Neptune was discovered in 1846, after analysis of Uranus’s orbit indicated its presence Details of Neptune cannot be made out from Earth either; arrows again point to moons: 13.3 Physical Properties of Uranus and Neptune Uranus and Neptune are very similar: 13.3 Physical Properties of Uranus and Neptune Uranus Neptune Mass 14.5 × Earth 17.1 × Earth Radius 4.0 × Earth 3.9 × Earth Density 1300 kg/m3 1600 kg/m3 13.3 Physical Properties of Uranus and Neptune Peculiarity of Uranus: axis of rotation lies almost in the plane of its orbit. Seasonal variations are extreme. 13.4 The Atmospheres of Uranus and Neptune Outer atmospheres of Uranus and Neptune are similar to those of Jupiter and Saturn Uranus and Neptune are cold enough that ammonia freezes; methane dominates and gives the characteristic blue color 13.4 The Atmospheres of Uranus and Neptune Uranus is very cold; clouds only in lower, warmer layers. Few features are visible: 13.4 The Atmospheres of Uranus and Neptune Band structure of Neptune is more visible, and Neptune has internal heat source of unknown origin: 13.4 The Atmospheres of Uranus and Neptune Neptune has storm systems similar to those on Jupiter, but fewer: 13.5 Magnetospheres and Internal Structure Uranus and Neptune both have substantial magnetic fields, but at a large angle to their rotation axes. The rectangle within each planet shows a bar magnet that would produce a similar field. Note that both Uranus’s and Neptune’s are significantly off center. 13.5 Magnetospheres and Internal Structure Magnetic fields of Uranus and Neptune must not be produced by dynamos, as the other planets’ fields are. Interior structure of Uranus and Neptune, compared to that of Jupiter and Saturn: 13.6 The Moon Systems of Uranus and Neptune 13.6 The Moon Systems of Uranus and Neptune Uranus has 27 moons, five of which are major: Miranda, Ariel, Umbriel, Titania, and Oberon Very similar to Saturn’s medium-sized moons, except that all are much less reflective. Umbriel is the darkest: 13.6 The Moon Systems of Uranus and Neptune Miranda is the most unusual; origin of the cracks and grooves is unknown: 13.6 The Moon Systems of Uranus and Neptune Neptune has 13 moons, but only two can be seen from Earth: Triton and Nereid Triton is in a retrograde orbit; Nereid’s is highly eccentric Triton’s surface has few craters, indicating an active surface 13.6 The Moon Systems of Uranus and Neptune Nitrogen geysers have been observed on Triton, contributing to the surface features: 13.6 The Moon Systems of Uranus and Neptune Also, there appear to be ice volcanoes: 13.7 The Rings of the Outermost Jovian Planets Uranus and Neptune have faint ring systems, recently detected. Uranus’s rings are narrow: 13.7 The Rings of the Outermost Jovian Planets Two shepherd moons keep the epsilon ring from diffusing: 13.7 The Rings of the Outermost Jovian Planets Neptune has five rings, three narrow and two wide: 13.8 The Discovery of Pluto Pluto was discovered in 1930. It was thought to be needed to explain irregularities in the orbits of Uranus and Neptune, but it turned out that there were no such irregularities. 13.8 The Discovery of Pluto Pluto’s orbit is eccentric and inclined to the plane of the ecliptic; it also crosses the orbit of Neptune: 13.9 The Physical Properties of Pluto Pluto’s moon, Charon, was discovered in 1978. It is orbitally locked to Pluto, and about a sixth as large. 13.9 The Physical Properties of Pluto Its orbit is at a large angle to the plane of Pluto’s orbit: 13.10 The Origin of Pluto The Kuiper belt is outside the orbit of Pluto, and has many icy chunks. Current theory is that Pluto is the nearest, and largest, of these objects. Summary of Chapter 13 • Uranus, Neptune, and Pluto were all discovered in the last 350 years • Uranus and Neptune are similar: gaseous and cold • Uranus’s spin axis is almost in the plane of its orbit • Surface features are hard to discern on Uranus, but more obvious on Neptune • Uranus has no excess heat emission, but Neptune does Summary of Chapter 13, cont. • Uranus’s midsized moons are similar to those of Saturn • Neptune’s moon Triton has a retrograde orbit • Uranus and Neptune both have faint ring systems • Pluto was discovered in 1930; its moon Charon in 1978 • Pluto is thought to be related to objects in the Kuiper belt