Meteor Showers 42 Entering Earth’s Atmosphere 46 Meteor Crater 50 Chapter3 Studying Meteorites 55 The Different Types of Meteorites 59 Chondrites 61 Chondrules 63 Meteoritics The Science of Meteors and Meteorites 64 Achondrites 65 Meteorites Composed of Iron 69 Association of Meteorites with Asteroids 71 Meteorite Craters 76 Meteorites and the Early Solar System 78
Chapter4 The Universe of Comets 85 Classifying Comets 87 Early Study of Comets 89 Modern Research 90 The Process of Discovery 93 Inside Comets 96 The Tail of the Comet 102 Origin and Evolution 108 Halley’s Comet 110 Conclusion 116 Glossary 117 Bibliography 120 Index 124
Sometimes one can see a flash of light streak across the night sky and disappear This is commonly called a shooting star though they are not stars They are small chunks of stone metal or other materials that orbit the Sun Sometimes they enter Earth’s atmosphere and the friction generated generated by their great speed causes them to burn up The fragments may either vaporize before traveling far or actually hit the ground These objects have different names depending depending on their location One that is beyond Earth’s atmosphere is called a meteoroid A meteoroid that enters Earth’s atmosphere is called a meteor A meteor that actually lands on Earth’s surface is called a meteorite Meteorites which are sturdy enough to reach the ground are mostly pieces of asteroids or huge rocks that orbit the Sun Comets on the other hand are flimsy objects made mostly of frozen water frozen gases and some gritty material They also orbit the Sun Meteoroids vary from small rocks to boulders weighing a ton or more A relative few have orbits that bring them into Earth’s atmosphere and down to the surface as meteorites Most meteorites that have been collected on Earth are probably from 6 INTRODUCTION
Comet Siding Spring appears to streak across the sky like a superhero superhero in this infrared image from NASA’s Wide-field Infrared Survey Explorer or WISE asteroids A few have been identified as being from the Moon Mars or the asteroid Vesta Most meteoroids that enter the atmosphere heat up sufficiently to glow and appear as meteors and the great 7
