Since the Big Bang • How Stars Live and Die • Dark Matter QUARTERLY $4.95 DISPLAY UNTIL MAY 31, 1998 PRESENTS SCIENTIFIC AMERICAN MAGNIFICENT OSMOS Other WorldsC Other Life Exploring MAGNIFICENT Exploding Galaxies the universe, Strange Radiation from our solar COSMOS neighborhood Multiple Universes to beyond Future Space Probes distant galaxies A PICTORIAL TOUR: TTHEHE PPLANETSLANETS Quarterly Number 1 9, Volume Saturn looms over Titan’s clouds Copyright 1998 Scientific American, Inc. MAGNIFICENT PRESENTS Spring 1998 Volume 9 Number 1 OSMOS I DISCOVERING WORLDSC 9 10 Giant Planets Orbiting Faraway Stars 22 Searching for Life Geoffrey W. Marcy and R. Paul Butler in Other Solar Systems The first-detected planets around other suns are al- Roger Angel and Neville J. Woolf ready overthrowing traditional theories about how Worlds supporting life have characteristics that new solar systems form. generations of telescopes and other instruments should be able to detect, even from light-years away. 16 Searching for Life in Our Solar System Bruce M. Jakosky 26 Planetary Tour The more that is learned about our neighboring A pictorial guide to the diverse, myriad worlds of planets and moons, the our solar system—from gas giants to wandering more hospitable pebbles—and their many peculiarities. some of them 28 Mercury 38 Saturn look as havens for life, today 30 Venus 40 Uranus or in the 32 Earth 42 Neptune distant 34 Mars 44 Pluto past. 36 Jupiter 46 Comets and Asteroids II FIRE AND LIGHT 49 50 SOHO Reveals the Secrets of the Sun Kenneth R. Lang Vibrations reverberating through the sun have sketched its complex anatomy. 2 Copyright 1998 Scientific American, Inc. Scientific American quarterly (ISSN 1048-0943), Volume 9, Number 1, 1998, published quarterly by Scientific American, Inc., 415 Madison Avenue, New York, N.Y. 10017-1111. Copyright © 1998 by Scientific American, Inc. All rights reserved. No part of this issue may be reproduced by any me- chanical, photographic or electronic process, or in the form of a phonographic recording, nor may it be stored in a retrieval system, transmitted or otherwise copied for public or private use without written permission of the publisher. Periodicals Publication Rate Pending. Postage paid at New York, N.Y., and at additional mailing offices. Canadian BN No. 127387652RT; QT No. Q1015332537. Subscription rates: one year $19.80 (outside U.S. $23.80). To purchase additional quantities: 1 to 9 copies: U.S. $4.95 each plus $2.00 per copy for postage and handling (outside U.S. $5.00 P & H); 10 to 49 copies: $4.45 each, postpaid; 50 copies or more: $3.95 each, postpaid. Send payment to Scientific American, Dept. SAQ, 415 Madison Avenue, New York, N.Y. 10017-1111. Postmaster: Send address changes to Scientific American, Box 3187, Harlan, IA 51537. Subscription inquiries: U.S. and Canada (800) 333-1199; other (800) 333-1199 or (515) 247-7631. 56 V1974 Cygni 1992: The Most III A UNIVERSAL VIEW 85 Important Nova of the Century Sumner Starrfield and Steven N. Shore 86 The Evolution of the Universe This supernova, one of the best studied of all time, P. James E. Peebles, David N. Schramm, gave up volumes of information not only about how Edwin L. Turner and Richard G. Kron stars die but also about how they live. Cosmologists have pieced together much about how the universe as we know it grew from a fireball instants 62 Cosmic Rays at the Energy Frontier after the big bang. Yet unanswered questions remain. James W. Cronin, Thomas K. Gaisser and Simon P. Swordy 92 The Expansion Rate and Atomic particles packing the wallop of a pitcher’s Size of the Universe fastball strike Earth’s atmosphere every day. Wendy L. Freedman How fast the universe is expanding and what its diam- 68 Gamma-Ray Bursts eter might be fundamentally limit cosmological theo- Gerald J. Fishman and Dieter H. Hartmann ries. New observations yield better estimates of both. Mysterious flashes of intense gamma radiation were spotted decades ago. Only in the past year 98 The Self-Reproducing has their cause become clear. Inflationary Universe Andrei Linde 74 Colossal Galactic Explosions Our universe may be just one infinitesimal part of a Sylvain Veilleux, Gerald Cecil “multiverse” in which branching bubbles of space- and Jonathan Bland-Hawthorn time contain different physical realities. At the heart of many galaxies rages a violent in- ferno, powered either by an ultramassive black 106 Dark Matter in the Universe hole or a burst of stellar birth. Vera Rubin Somewhere in space hide masses of “dark matter” that hold together galaxies and galactic clusters. Its 80 The Ghostliest Galaxies nature and quantity rule the fate of the universe. Gregory D. Bothun Half of all the galaxies in the observable universe 112 A Scientific Armada may have been overlooked for decades because Tim Beardsley they were too large and diffuse to be readily noticed. A guide to upcoming space missions. 3 Copyright 1998 Scientific American, Inc. F ROM THE EDITORS ® Treasures in the Stars PRESENTS xploration of space has sprinted forward over the past two Magnificent Cosmos is published decades, even though no human has ventured outside the lunar by the staff of Scientific American, Eorbit. Thanks to strings of probes with names like Voyager, with project management by: Pioneer, Galileo, Magellan and SOHO, planetary and solar science thrived. We have seen all the planets but Pluto from close by, visited John Rennie, EDITOR IN CHIEF Mars and Venus by proxy, and even witnessed the collision of Comet Michelle Press, MANAGING EDITOR Shoemaker-Levy with Jupiter. The moons graduated from minor players Richard Lipkin, ISSUE EDITOR to varied, exotic worlds in their own right and possibly to abodes for life. Sasha Nemecek, ASSISTANT EDITOR The sun revealed its complex internal anatomy. Whole new classes of STAFF WRITERS: Timothy M. Beardsley; frozen bodies beyond Neptune’s orbit came into view. Steve Mirsky; Madhusree Mukerjee; Glenn Zorpette Meanwhile the magnificent Hubble Space Telescope, other orbiting Art instruments and their Earth-bound cousins peered clearly into deeper Edward Bell, Jessie Nathans, ART DIRECTORS space. They showed us new types of galaxies and stars, spotted planets Bridget Gerety, PHOTOGRAPHY EDITOR Meghan Gerety, PRODUCTION EDITOR around other suns and took the temperature of the big bang. We better appreciated our own solar system after seeing how fiercely bright some Copy Maria-Christina Keller, COPY CHIEF corners of the universe burn. Molly K. Frances; Daniel C. Schlenoff; With this issue, Scientific American summarizes the most extraord- Katherine A. Wong; Stephanie J. Arthur; William Stahl inary discoveries and still open mysteries of modern astronomy. It also Administration debuts the new series of Scientific American Presents quarterlies, each of Rob Gaines, EDITORIAL ADMINISTRATOR which will look in depth at a single topic in science or technology. (The Production Richard Sasso, ASSOCIATE PUBLISHER/ regular monthly magazine will, of course, continue to scan the full range VICE PRESIDENT, PRODUCTION of disciplines.) William Sherman, DIRECTOR, PRODUCTION Janet Cermak, MANUFACTURING MANAGER Tanya DeSilva, PREPRESS MANAGER ll the authors of this issue deserve thanks for their fully new articles Silvia Di Placido, QUALITY CONTROL MANAGER Carol Hansen, COMPOSITION MANAGER Aor for the extensive updates they made to previous works. But I Madelyn Keyes, SYSTEMS MANAGER must with sadness extend special appreciation to the late cosmologist Carl Cherebin, AD TRAFFIC; Norma Jones David N. Schramm, whose untimely death in December 1997 Circulation immediately followed our collaboration. We mourn him for both his many Lorraine Leib Terlecki, ASSOCIATE PUBLISHER/ CIRCULATION DIRECTOR kindnesses and his scientific vision. I am grateful also to the Lockheed Katherine Robold, CIRCULATION MANAGER Joanne Guralnick, CIRCULATION PROMOTION MANAGER Martin Corporation for its generous offer to become the sole sponsor of Rosa Davis, FULFILLMENT MANAGER this issue; such financial support, unfettered by editorial constraints, helps Advertising to ensure that we can bring to readers the information they crave at a price Kate Dobson, ASSOCIATE PUBLISHER/ADVERTISING DIRECTOR they can afford. My deepest gratitude, though, goes to editor Rick Lipkin OFFICES: NEW YORK: Thomas Potratz, EASTERN SALES DIRECTOR; and, as always, the rest of the staff of Scientific American, for their unfail- Kevin Gentzel; Stuart M. Keating; Timothy Whiting. ing industry and love of good science. DETROIT, CHICAGO: 3000 Town Center, Suite 1435, Southfield, MI 48075; Edward A. Bartley, DETROIT MANAGER; Randy James. WEST COAST: 1554 S. Sepulveda Blvd., Suite 212, Los Angeles, CA 90025; Lisa K. 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The cover image Ancillary Products Diane McGarvey, DIRECTOR offers a perspective just above the methane clouds of the Scientific American, Inc. 415 Madison Avenue • New York, NY 10017-1111 moon Titan as it orbits Saturn. (212) 754-0550 PRINTED IN U.S.A. 6Scientific American Presents Copyright 1998 Scientific American, Inc. I Discovering Worlds • GIANT PLANETS ORBITING FARAWAY STARS • SEARCHING FOR LIFE IN OUR SOLAR SYSTEM • SEARCHING FOR LIFE IN OTHER SOLAR SYSTEMS • PLANETARY TOUR JUPITER AND IO RISING, as seen from Europa, a moon of Jupiter ILLUSTRATION BY DON DIXON ILLUSTRATION Copyright 1998 Scientific American, Inc.