CONTENTS INTRODUCTION CHAPTER 1 CHARACTERISTICS OF MERCURY 10 CHAPTER 2 PHYSICAL FEATURES AND ExPLORATION OF MERCURY 19 CHAPTER 3 CHARACTERISTICS OF Venus 28 CHAPTER 4 PHYSICAL FEATURES AND EXPLORATION OF VENUs 35 CHAPTER 5 CHARACTERISTICS OF MARS 53 CHAPTER 6 PHYSICAL FEATURES AND EXPLORATION OF MARS 62 CONCLUSION GoSSARY For MORE INFORMATION BIBLIOGRAPHY 87 88 90 92 93 INDEX
ince ancient times humans have gazed in wonder at the vast blanket of stars covering the night sky Records going back 5 000 years show that ancient Sumerian astronomers recognized that some stars moved differently than other celestial bod ies Three special objects they tracked are the three closest planets to Earth Mercury Venus and Mars These objects still fascinate today This book will take you on a journey to learn about our neighbors in the solar system The first stop on our tour will be tiny Mercury At less than two fifths Earth s size it is the smallest of the eight planets Because it is the closest planet to the Sun it can complete an orbit around the Sun in only 88 Earth days But it takes almost 59 Earth days to complete one rotation about its axis Mercury has almost no atmosphere leaving its dry and rocky surface little protection from crater blasts by asteroids Mercury is the densest planet in the solar system Our second stop is Venus the solar sys tem s third smallest planet and the one most similar in size to Earth Venus's atmosphere is remarkably massive Made mostly of thick heat trapping layers of carbon dioxide the heavy atmosphere makes it the hottest planet
INTRODUCTION in the solar system This thick atmosphere has also made it difficult to study the planet s surface Venus's orbit and rotation are also unusual A year on Venus is 225 days But the planet spins about its axis very slowly com pleting one rotation about every 243 Earth days making Venus the only planet in the solar system that takes longer to rotate once about its axis than to travel once around the Sun Venus and Uranus are also the only two planets that rotate counterclockwise The third stop on our journey Mars the second smallest planet in the solar system is only about half Earth's size The planet com pletes one revolution around the Sun in about 687 Earth days A Martian day lasts a little longer than 24 hours It also has two small potato shaped moons Observers have long wondered if there was life on Mars because it appears as if there are channels that might once have contained water a necessary ingre dient for life In fact there still is water on Mars but most of it is frozen beneath the planet s surface The thin atmosphere doesn't shield the surface from harsh ultraviolet radi ation or from being hit by space junk Since the beginning of the space age humans have had the power to do more than
