American Institute of Aeronautics and Astronautics, Inc., Reston, Virginia

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Library of Congress Cataloging-in-Publication Data on file.

ISBN 1-56347-776-9

Front Cover:

Shadows cast by Saturn's rings on the planet's cloud tops form a backdrop to the moon Mimas in this stunning true-colour view from NASA's Cassini spacecraft. Mimas is 400km across and orbits 185,000 km above the planet. Cassini was 1.4 million km from Saturn when it took this image on 18 January 2005. [NASA/JPL/Space Science Institute]

Back Cover:

Upper image: The ultimate iconic image of the 20 ^th century - but how long will Aldrin' s boot print survive once the lunar tourists arrive? [NASA]

Lower image: A 'frozen sea' near the Martian equator - part of the Martian environment worth protecting. [ESA/DLR/FU Berlin (G. Neukum)]

Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. No part of this publication may be reproduced, distributed, or transmitted, in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher.

To Rita, Matthew, and Thomas. Three stars in a fragile universe.

Acknowledgments

I am indebted to a number of friends and colleagues for the time they gave so freely in reviewing sections of the original manuscript and would like...