The Outer Planets: Jupiter, Saturn, Uranus, and Neptune
THE OUTER PLANETS JUPITER SATURN URANus AND NEPTUNE Volcanoes erupt on lo one of Jupiter s Galilean satellites in a mosaic of images captured by the Galileo spacecraft One plume visible on lo at the far left is about 90 miles 40 kilometers high Another plume at the center of the moon is revealed by its shadow which extends to the right Photo NASA JPL Caltech NASA photo PIAo1081
INTRODUCTION about a dozen narrow rings which are not as bright as Saturn's and 27 known moons Like Jupiter and Saturn this planet is not solid It is made up of hydrogen helium water and other compounds Finally we arrive at the farthest planet from the Sun Neptune At more than 2 5 bil lion miles 4 billion kilometers from Earth Neptune was not discovered until the mid 1800s Although Neptune is the smallest of the four outer planets it is the densest Neptune is a gas giant too and is primar ily made up of hydrogen and some helium Pressures in the planet s interior are likely high enough to render it liquid Neptune spins so quickly that a day one rotation lasts only 16 hours Neptune has a series of six rings and four of the planet s 13 moons orbit within the rings Curiously one of Neptune s moons Titron revolves around the planet in a direction opposite the planet s rotation For many years Jupiter Saturn Uranus and Neptune were shrouded in mystery Astronomers have much to learn about this quartet of gas giants Probes such as Voyager 1 and 2 have gathered enough data and pho tographs to present a broader picture of the planets rings and moons that you will learn about in these pages 9
hapter CHARACTERISTICS OF JUPITER NNhe fifth planet from the Sun and the solar system s largest planet by far is Jupiter More than 1 300 Earths would fit inside it The planet is one of the bright est objects in the night sky and even a small telescope can reveal its multicolored stripes These stripes are bands of clouds being pushed around the planet by strong east west winds Jupiter is a world of complex weather patterns Its most prominent feature is an orange red oval called the Great Red Spot The oval is a storm system that has lasted at least 300 years and is bigger across than Earth and Mars combined Bands of pastel colored clouds encircle the giant planet Jupiter which appears in a composite of images taken by the Cassini space craft The small black disk at lower left is a shadow cast by Jupiter's moon Europa The enormous storm called the Great Red Spot is visible at lower right The raw images were taken in two colors which were processed to simulate Jupiter's natural colors NASA JPL University of Arizona
CHARACTERISTICS OF UPITER Jupiter is not just bigger than Earth it is also fundamentally different in composition Jupiter has no solid surface It is formed of the same elements in roughly the same propor tions as the Sun and other stars Like Saturn it is made almost entirely of hydrogen and helium in liquid and gaseous forms Although A map shows the entire visible surface of Jupiter including its bands of clouds the Great Red Spot and many smaller oval storms in the planet's massive atmosphere The map is a cylindrical projection like maps of Earth that show the planet stretched flat onto a rectangle It was generated by computer from 36 images taken by the Cassini space craft and processed to simulate the planet's true colors Jupiter's polar regions appear less clear because of the angle of the spacecraft Scam era and because they were covered by a thicker base NASA JPL Space Science Institute II
