The Outer Planets

The Outer Planets — page 1 — Jupiter’s Other Satellites 41 Jupiter’s Ring 42 Chapter2 Saturn The Jewel of the Solar System 46 An Overview of Saturn 48 Composition and Structure of Saturn’s Atmosphere 52 A Dynamic Atmosphere 55 The Magnetic Field and Magnetosphere 57 Saturn’s Interior 60 Saturn’s Complex Ring System 63 Discovering Saturn’s Rings 64 Saturn’s Moons 69 Chapter3 Uranus An Ice Giant 76 Astronomical Data of Uranus 78 The Atmosphere of Uranus 81 The Magnetic Field and Magnetosphere 83

The Outer Planets — page 2 — The Interior 86 Moons of Uranus 89 The Ring System 95 Discovery of the Rings 96 Chapter4 Big Blue Neptune 99 Neptune An Overview 101 Neptune’s Atmosphere 103 The Magnetic Field and Magnetosphere of Neptune 106 The Origin of Neptune’s Orbit 108 Neptune’s Interior 110 The Moons and Rings of Neptune 110 Conclusion 118 Glossary 119 Bibliography 122 Index 126

The Outer Planets — page 3 — Of the eight planets in our solar system Jupiter Saturn Uranus and Neptune are called the outer planets They are much larger than the inner planets and have deep gaseous atmospheres Because of this they’re sometimes nicknamed the gas giants Since Jupiter being the largest is the outstanding representative of this group the four outer planets are also known as the Jovian or Jupiter-like planets The outer planets have no solid surfaces Jupiter Jupiter and Saturn consist mainly of liquid and gaseous hydrogen and helium Uranus and Neptune have melted ices and molten rock as well as hydrogen and helium All the outer planets are less than twice as dense as water In fact Saturn’s density is so low that it would float if put in water The inner planets Mercury Venus Earth and Mars formed at temperatures too high to allow the abundant volatile substances those with comparatively comparatively low freezing temperatures such as water carbon dioxide and ammonia to condense to their ices They therefore remained small rocky bodies In contrast the large low-density gas-rich outer planets formed at distances beyond what astronomers astronomers have dubbed the snow line the minimum radius from the Sun at which water ice could have 6

The Outer Planets — page 4 — IntroductIon condensed With the outer planets the accretion of icy planetesimals produced objects with masses 10 times that of Earth sufficient to cause the gravitational collapse of the surrounding gas and dust in the solar nebula These planets grew so large that their composition approached that of the Sun itself with hydrogen and helium the dominant dominant elements Each of the outer planets has a magnetic field a ring system and many known moons with more likely to be discovered Most of the known moons move around their respective planets in the same direction that the planets orbit the Sun The moons are extremely diverse representing a wide range of environments Jupiter is orbited by Io a body wracked by intense volcanism while Saturn’s largest moon Titan a body larger than Mercury exhibits a primitive atmosphere denser than that of Earth Triton moves in a retrograde orbit around Neptune that is opposite to the direction of the planet’s orbit around the Sun and features plumes of material rising through its tenuous atmosphere This book explores the characteristics of each of the outer planets and their moons Jupiter is the most massive massive of the solar system more than 1,300 Earths would fit inside it and the fifth in distance from the Sun It is a world of extreme and complex weather patterns including an orange-red oval called the Great Red Spot a long-lasting 7

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