On the Cover: Volume XIX It's beautiful; it changes each time we see it. It's [0, the most Table of Number 4 ,volcanically active object in human experience. This look is from Galilee's 10th orbit through the Jupiter system. On previous Contents July/August 1999 orbits, the red halo surrounding the volcano Pele was the most prominent feature in the southern hemisp he re . On the 9th orb it, Galilee saw a gigantic plume, 120 ki lomete rs (75 mil es) high, from an eruption near Pele , from a volcanic center called Pillan Patera. On the next orbit, a large, dark feature, 400 kilom eters Features (about 250 miles) in diamete r, had broken Pele's red halo­ one of th e most dramatic chan ges seen on 10. Galileo took th is Opinion: Why Is the Day 24 Hours.. and image on September 19, 1997 from a distance of 500,000 4 When Will the Millenniul'l"l Begin? kilometers (about 310,000 miles). Owen Gingerich of the Harvard-Smithsonian Center for Astrophysics is one of Earth's Image: JPUNASA preeminent historians of science. When he talks, other scholars listen. This question of when to mark the end of the current millennium is one of the most contentious we've heard at the Planetary Society. So, here it is, our unofficial final word on the subject. 8 In the Beginning Froln Since the Planetary Society began nearly 20 years ago, Jim Burke has been our resident "Moon man." The recent confluence of experimental results from Lunar Prospector and The theoretical advances regarding the origin of Earth's natural satellite have placed Jim in the Editor lunar equivalent of hog heaven. He reflects on Earth and Moon's shared story, and the history of humanity'S attempts to understand their origins, in this essay that shares his passion with our members. aving a century and millennium end at H the same time can addle the editorialist's 12 Ga'i'eo: On to 10 and Cassini brain. (And before sending me flaming mes­ Galileo's saga must be the most complex in the history of our explorations of sages about when the millennium actually ends, other worlds. It began in the 1970s as designs for a mission called JOP, for Jupiter Orbiter read the article that begins on page 4.) You and Probe. It evolved over the years into Galileo, one of the most complex and ambitious look back across what you know of time and planetary missions ever planned. Approved in 1977 and scheduled to launch in 1982, the see that we humans have moved by fits and spacecraft waited while NASA's problems with the space shuttle forced postponement after postponement. Finally, in 1989, it set offfor Jupiter and arrived in 1995. There, over starts to reach this beginning ofthe Space Age. the course of two years, it completed its primary mission, dropping a probe into JupIter's For centuries, humans dreamed of flight, and atmosphere and studying the planet and its large satellites. In 1997, the spacecraft was we achieved it in 1903. Only 66 years later, a hardy enough to carry out the Galileo Europa Mission for the next two years. And now, a mere two-thirds of a century, we walked on the bit doddery but still functional, Galileo undertakes another task: a rendezvous with Cassini. Moon. I remember those heady days ofyester­ year when people believed that before the cen­ tury was out, we would walk on Mars. Departlnents Instead, there are only 12 sets offootprints on the Moon. There are no plans to place any 3 Mel'l"lbers" Dialogue more footprints on that first stepping-stone into space. And the more time passes, the far­ 18 Nevvs and Revievvs ther away Mars seems. All I have to say is: "Thank heavens for 1 9 World Watch robots." Lunar Prospector is about to crash itself into the Moon in a final search for 20 Questions and Ansvvers water. Galileo is steadfastly maintaining its watch at Jupiter in hopes of "meeting" 22 Society Nevvs Cassini as the Saturn-bound spacecraft flies past. These and other robotic craft are keep­ ing alive the dream of exploring other worlds. We went from longships to spaceships in the Contact Us last millennium, and from the Wright Flyer to Apollo's Eagle in the last century. How long Mailing Address: Th e Planetary SOCiety, 65 North Catalina Avenue, Pasadena , CA 91106-2301 until we talk ourselves onto another world? General Calls: 626-793-5100 Sales Calls Only: 626-793-1675 - Charlene M. Anderson E-mai l: tps@mars. pl anetary.org World Wide Web: http ://planetarY.org ~;~~~e~~c:m~3~~~~~?7l~6~?g~~~~g~~:~s~e~v~ji~~~~h~~ a~~~~g;~o~rltg~i~~inO~t~r~ ~~~i~~7 t~~~·d6~e~~~t~h~a~~n:r:$e2n~e. (US dollars); in Canada, $35 (Canadian dollars). Dues i.n other countries are $40 (US dollars). Printed in USA. Third-class postage at Pasadena, California. and at an additional mailing office. Canada Post Agreement Number 87424 A Publication of Editor, CHARLENE M. ANDERSON Technical Editor, JAMES D. BURKE Associate Editor, DONNA ESCANDON STEVENS Copy Editor, KARL STULL THE-PL.A~T1RV SOCIETV Assistant Editor, JENNIFER VAUGHN Proofreader, LOIS SM ITH 0 Proquction Editor, WILLIAM MCGOVERN Art Director, BARBARA S. SMITH o .~ -e- cp -& 0 Viewpoints expressed in columns or editorials are thoseo f-the authors and do not necessarily represent positions of the Planetary Society, • its officers, or advisors. ©1999 by the Planetary Society. --- -- ~I Members' 1934'19~; I Board of Directors I BRUCE MURRAY Dialogue President Professor of Planetary Science and Geology, California Institute of Technology LAUREL L. WILKENING Vice President former Chancellor, University of California. Irvine LOU IS D. FRIEDMAN Executive Director NORMAN R. AUGUSTINE Chairman and CEO, Lockheed Martin Corporation ANN DRUYAN author and producer DONALD J. KUTYNA Let's Save Mir Pluto's Place ofusing names ofmole cules former Commander, US S(JEce Command In a recent magazine, a reader pro­ Clark Chapman's News and rather than formulas. (DIe Calvin s JOSEPH RYAN Executive Vice President and posed boosting Mir to lunar orbit, Reviews on the planetary standing original manuscript referenced General Counsel, Marriotf International ROALD l. SAGDEEV rather than "waste it" by allowing of Pluto (see the Marchi April 1999 these molecules as CH30H and former Director, Institute for S(JEce Research, Russian Academy of Sciences it to burn up in the atmosphere. Planetmy Report) was quite amus­ H2Co.) Thanks to Tom Kuiper[or STEVEN SPIELBERG I read in today's newspaper that ing. Why do seemingly intelligent bringing the common names to director and producer KATHRYN D. SULLIVAN Russia will cut off funding in people waste precious time argu­ our attention, plus two highly President and CEO, Ohio's Center of Science and Industry August. ing about such mundane matters interesting Web sites. and former astronaut Notwithstanding the technical as whether Pluto should retain - Charlene M. Anderson, NEIL DE GRASSE TYSO N Director, Hayden Planetarium. challenges involved, I think this planetary status? Associate Director American Museum of Natural History reader may be on to something The whole question is a moot Advisory Council big, and I encourage the Society to point, because by very definition The True Story JOHN M. LOGSDON Chairman Director, S(JEce Policy Institute, immediately start a more detailed of the word planet, even Earth James Pinkham's letter in the Marchi George Washington University dialogue on this issue! Mir in doesn't qualify. To the ancients, April 1999 issue isn't quite correct DIANE ACKERMAN lunar orbit could offer a giant leap the word planet meant "wander­ on one point: for once the United poet and author JIHEI AKITA toward a permanent human pres­ ing star." That means none of the States Patent Office calIDot be Executive Director. The Planetary Society, Ja(JEn BUll ALDRIN ence on the Moon. It could imme­ bodies circling the Sun are planets. blamed! I never attempted to patent Apollo 11 astronaut diately pay dividends by acting as These bodies do not wander­ the communications satellite, RICHARD BERENDlEN educator and astrophysicist an equipment platform for a sys­ they have remarkably stable largely because I never dreamed it JACQUES BLAMONT Chief Scientist. tematic human search for the best orbits. They are not stars for they would happen in my lifetime. (I was Centre National d'Etudes Spaliales, France lunar base site and location of do not generate nuclear fusion. also helping to finish a war ... ) RAY BRADBURY poet and author frozen water deposits on the Moon I suppose we will have to sim­ Pinkham may be referring to DAVID BRIN from lunar orbit instead of Earth! ply refer to all of these bodies as an amusing spoofby patent lawyer author FRANKLIN CHANG·DIAl Perhaps an aging space shuttle, rocks. We are the third rock from Ted Thomas called "The Lagging NASA, Astronaut Office ARTHUR C. CLARKE unable to take the rigors of Earth­ the Sun (which is really a star). Profession" (by Leonard Lockhard) author return gravity, could be used as a - RANDY W. MURRAY, in the January 1961 issue of Analog. FRANK DRAKE President, SETI/nst/tule; permanent Earth-Moon (orbit to Clearwater, Florida This described an attempt by me Professor of Astronomy and Astrophysics, University of California, santa Cruz orbit only) shuttle craft, carrying to do just this, which had the STEPHEN JAY GOULD Alexander Agassiz Professor of ZOOlogy, crew and cargo between the Inter­ Solar Systenl Ices results he mentions. Harvard University national Space Station and Mir in The compounds methyl hydJ.-oxide -ARTHUR C.