A Publication of THEPLANE~ SOCIETV

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Board of Directors FROM THE CARL SAGAN BRUCE MURRAY EDITOR President Vice President Director, Laboratory for Planetary Professor of Planetary Studies, Cornell University Science, California Institute of Technology LOUIS FRIEDMAN Executive Director JOSEPH RYAN O'Me/veny & Myers MICHAEL COLLINS Apollo 11 astronaut STEVEN SPI ELBERG director and producer THOMAS O. PAINE former Administrator, NASA HENRY J. TANNER s I write this, four members of The Page 12-Tracking Asteroids: Why We Chairman. National financial consultant Commission on Space A Planetary Society's Mars Rover team Do It-Asteroids have also been neglect­ Board of Advisors are on the Kamchatka Peninsula testing the ed members of the solar system, but that

DIANE ACKERMAN JOHN M. LOGSDON prototype mobile robot. Their timing was is changing, in part due to the efforts of poet and author Director, Space Policy Institute, George Washington University impeccable: They left for Siberia on the The Planetary Society. As part of our as­ ISAAC ASIMOV author HANS MARK day of the attempted coup in the Soviet teroid program, we are helping to fund the Chancellor, RICHARD BERENDZEN University of Texas System Union. efforts of Jeremy Tatum at the University educator and astrophysicist JAMES MICH ENER While the Society' sstaff never really of Victoria. Here he reports to members JACOUES BLAMONT author Chief Scientist. Centre feared for their safety, we were relieved to on his work. National d 'ElUdes Spatiafes, MARVIN MINSKY France Toshiba Professor of Media Arts receive a fax from the Institute for Space Page 16-The 1991 Solar Eclipse From and Sciences, Massachusetts RAY BRADBURY Institute of Technology poet and author Research in Moscow which read: "TPS a Different Perspective-A member's PHILIP MORRISON ARTHUR C. CLARKE team is OK and comfortable. They enjoy suggestion has enabled his fellow mem­ Institute Professor, Massachusetts atJlhor. Institute of Technology good weather and food." bers to view the solar eclipse from an CORNELIS DE JAGER Professor of Space Research. PAUL NEWMAN We will bring you more details of this unusual perspective-,-from space. The Astronomiea/lnstitute at actor Utrecht, The Netherlands JUN NISHIMURA expedition in upcoming Planetary Reports. Page 19-International Space Year Cel­ FRANK ORAKE Director-General, Institute of Space With the Soviet situation changing daily, ebrates Tomorrow's Explorers-1992 Professor of Astronomy and and Astronautical Sciences, Japan Astrophysics, University of we will be keeping a close watch on our has been designated as International Space California at Santa Cruz BERNARD M. OLIVER Chief, SET! Program, LEE A. DUBRIDGE NASNAmes Research Center cooperative projects with the Soviet space Year and at The Planetary Society we are former presidential science advisor SALLY RIDE agencies. planning a series of events to celebrate it. Director, California Space Institute, JOHN GARDNER University of California at Page 3-Members' Dialogue-With the Page 20-Questions & Answers-Dating founder, Common Cause San Diego. and former astronaut Magellan radar-mapping mission discover­ the martian surface, why Venus rotates MARC GARNEAU ROALD Z. SAGDEEV Canadian astronaut former Director, ing new geologic features on Venus nearly "backwards," traveling to an asteroid and Institute for Space Research, GEORGIY GOLITSYN Academy of Sciences of the USSR Institute of Atmospheric Physics, every day, the naming of these features be­ using gravity to reach the planets are the Academy of Sciences of the USSR HARRISON H. SCHMID comes a monumental task. In this column, topics we cover here. TH EODORE M. HESBURG H former US Senator, NM, and Apollo 17 astronaut President Emeritus, Professor William Kaula of UCLA takes Page 22-World Watch-We have two University of Notre Dame S. ROSS TAYLOR issue with some of the naming practices. guest columnists for this issue to bring SH IRLEY M. HUFSTEDLER Professorial Fellow, Aus/rafian educator and jurist National University, Canberra Page 4-A Morning With Philip Mor­ you reports on the recent Mars Balloon GARRY E. HUNT LEWIS THOMAS space scientist, Chancel/or, Memorial Sloan rison-In The Planetary Report we do meeting in Moscow and an upcoming United Kingdom Kettering Cancer Center not often cover gedanken experiments­ workshop on small spacecraft. SERGEI KAPITSA JAMES VAN ALLEN Institute for Physical Problems, Professor of Physics, thought experiments conducted in the Page 23-Society Notes-As the Society Academy of Sciences of the USSR University of Iowa imagination rather than the laboratory. grows and diversifies, we have more and

The Planetary Report (ISSN 0736-3680) is published six times yearly at However, such exercises can be fun. In more news, requests and offers. This col­ the editorial offices of The Planetary Society, 65 North Catalina Avenue, Pasadena, CA 911 06, (8 18) 793-5100. It is available to members of The this article, the director of our Project umn will keep you up to date. Planetary Society. Annual dues in the US or Canada are $25 US dollars or $30 Canadian. Dues outside the US or Canada are $35 (US) . MET A takes you up in a gedanken rocket -Charlene M. Anderson Editor, C HARLENE M . ANDERSON ship to enter the minds of those beings­ Technical Editor, JAMES D. BURKE Assistant Editor, DO NNA ESCANDON STEVENS if any-that might be trying to communi­ Copy Editor, G LORIA JOYCE cate with us across the vastness of space. The Planetary Society'S Art Director, BARBARA S. SMITH Annual Catalog Viewpoints expressed in columns or editorials are those of the authors and Page 8-A Clean, Well-Lighted Place: do not necessarily represent positions of The Planetary Society, its officers or advisors. © 1991 by The Planetary Society. Mercury-As in any large family, some Bound into the center of this issue you In Canada. Second Class Mail Registfation Number 9567 members of our solar system receive more will find our annual sales catalog. We COVER: Clouds of interstellar dust obscure the view attention than others. The planet Mercury publish this catalog once a year as a of our galaxy's central region which, viewed from has been vi sited by only one spacecraft, service to our members who might be Earth, lies in the direction of the constellation of and when lists of future mission targets are looking for distinctive holiday gifts. Sagittarius. With our solar system situated on the outskirts of the Milky Way, most of its stars appear drawn up, it is usually not ranked very If you prefer your Planetary Report within or beyond the galactiC center. If any galactic high. However, this small world does have without this sales insert, it can be easi­ beacon engineers are beaming a message our way, chances are it will come from that direction. Part of its partisans: Our News & Reviews colum­ ly removed. But we hope you first take the fun of the Search for Extraterrestrial Intelligence nist, Clark Chapman, has contributed an a look at the many entertaining and is trying to guess how another technological civi­ article on Mercury to this issue instead of IizlItion might try to contact ours. educational items that we offer. Photograph: David Malin, Anglo-Australian Observatory his regular feature. NEWS BRIEFS

As of late July, Magellan had col­ lected radar images of nearly 90 As administrators of a membership organization, The Planetary Society's Directors and staff percent of Venus' surface. The care about and are influenced by our members' opinions, suggestions and ideas about the future of the space program and of our Society. We encourage members to write us and create data set is double the amount of a dialogue on topics such as a space station, a lunar outpost, the exploration of Mars and the all other image data collected in search for extraterrestrial life. the United States planetary pro­ Send your letters to: Members' Dialogue, The Planetary Society, 65 N. Catalina Avenue, gram to date, said Steve Saunders, Pasadena, CA 91106. Magellan Project Scientist. -from a NASA press release While browsing over the United States Geological Survey's chart of Venus' northern quadrant, I noticed a feature named "Schumann-Heink Patera," and thought, "That's digging rather deep in a favorite category. There must also be features named Callas, Flagstad, Ponselle, Melba-all A group of frustrated space sta­ much more famous and influential as opera singers than Schumann-Heink." But none of them tion engineers calling itself the were there, and in the process of looking I found other oddities: obscure novelists like Prichard Center for Strategic Space Studies and Voynich and Lagerlof, but not Austen or Bronte or Woolf; rulers who were defeated, like in Reston, Virginia, has begun cir­ Boedicia and Cleopatra, but not those who were successful, like Elizabeth Tudor, Eleanor culating a detailed concept paper d'Aquitaine and Catherine the Great; and the only Indians were bedmates of European explor­ recommending that NASA slow ers-Malintzin, Pocahontas and Sacajawea. Most odd were Corday, the little assassin unknown work on the estimated $30 billion till she killed Marat, and Tituba, the black stimulator of the hysterias that led to the Salem trials. outpost in favor of refurbishing Are terrorism and witchery back in vogue? and launching the backup Skylab Names on Venus, like those on other planets, are chosen by a committee of the International orbiting workshop now sitting Astronomical Union (IAU), under a set of 13 rules, such as: "unambiguous," "prominent in any in the National Air and Space of the six main living religions are not acceptable," "dead at least three years," and no "special Museum in Washington, DC. individual or national significance." However, the interpretation is sometimes strange. Thus the The engineers behind the updat­ "unambiguous" seems strained when there is someone else more famous of the same name. On ed Skylab Plus proposal believe the provisional list are a "Graham," who is not the pioneer of modern dance, but a 19th-century the museum piece has substantial geologist; a "Lehmann," not either Lilli or Lotte, famous opera singers, but Inge, a seismologist capabilities as a human-tended (still alive at 103); and a "Danilova," not the 20th-century star of the Ballet Russe, but another materials-processing laboratory ballerina who died at 17 in 1810. that have not been eroded by the A teenager deservedly on the list is Anne Frank, but Jeanne d' Arc is not-presumably be­ millions of tourists who have cause she is "prominent" in Catholicism. Jeanne's main association with that institution was to viewed the workshop through be burned at the stake at age 19. The Church apparently decided it made a mistake (489 years holes cut in its tank superstructure. later) and made her a saint. A lot smarter was Queen Isabella of Spain ("Isabella Cat6lica" in They say it could be refurbished nearly all Spanish histories), who is proposed to be honored by a large crater (thus breaking the and launched for about $4 billion implicit rule of only defeated rulers). In 1478 pious Isabella petitioned the pope to institute the aboard the still conceptual Spanish Inquisition, which led to about 14,000 people being burned at the stake by the time she NASA/Air Force National Launch died in 1504. And in 1492, less than three weeks before commissioning Columbus, she signed System or the Soviet Union's the edict compelling all Jews to leave Spain within three months, resulting in well over 10,000 Energia heavy-lift booster. more deaths of the unfaithful from starvation and disease on the way to exile. One wonders -from Space News about the IAU's definition of "prominent." Your piece "What to Call the Crater?" in the NovemberlDecember 1990 Planetary Report says, "The system ensures that an international panel of experts names features in a fair and A new flaw has been discovered evenhanded way." Whatever the panel is expert in, I bet it's not history, literature or the arts. in a mirror on the Hubble Space -WILLIAM M. KAULA, Los Angeles, California Telescope, crimping a key instru­ ment's ability to analyze light Thanks for addressing the space station issue in World Watch [see the May/June issue of The from faint celestial objects. The Planetary Report] . I support The Planetary Society'S stance. NASA, in an attempt to appease problem is a buildup of aluminum special-interest groups and gain public support, has again put all its eggs in one basket. It is in oxide in the mirror of the faint­ jeopardy of committing the same mistakes that eventually led to the Challenger accident. object spectrograph, an instru­ Let us (the United States and humans in general) build a space program on a steady step-by­ ment designed to answer some step basis: robotIC missions, space sciences, then a new launch vehicle, a Skylab-type space fundamental questions about the station and so on ... to the Moon and Mars. Keep the issues coming. universe through the study of -MARK PIEKNY, Metairie, Louisiana light. The buildup apparently occurred If a long-duration space mission is not to be an ordeal for the crew, it is likely that artificial while the instrument sat in stor­ gravity will be a requirement. Isn't it more reasonable to develop a space station that has age during much of the 1980s artificial gravity before spending huge sums on more manned mega-projects? It might even be awaiting the telescope's launch. possible to construct a rotating space station in modular fashion without the use of a heavy-lift It went undetected until recently, launch vehicle, but the concepts involved should first be tried on a small scale. said George F. Hartig, the spec­ The United States space program hasn't lost its spark, but where nothing is ventured, trograph's chief scientist. nothing is gained. -from Edwin Chen in the -VICTOR COHEN, New York, New York Los Angeles Times 3 Exploring the by Paul Horowitz

n a gorgeous day last spring beautifully crafted inner workings. that we might do well to stop worrying (Thursday the 13th of June, to We spread out in the second-story so much about the search variable of Obe exact), the author spent a greenhouse, where I expected the dis­ wavelength, and assume instead that an stimulating morning with Professor cussion to focus on narrow technical interstellar beacon would most likely be Philip Morrison and Dr. Michael Davis, issues, such as the optimum receiver transmitted at a guessable wavelength discussing the Search for Extraterrestri­ bandwidth and resolution to design into (for example, the famous 21-centimeter al1ntelligence (SET!). Phil is a pioneer our next-generation search apparatus. line at which neutral hydrogen emits in SET!, having co-authored with This seemed natural, especially since naturally). Furthermore, the transmitting Giuseppe Cocconi the oft-quoted 1959 two weeks earlier Phil had chaired a civilization would finesse the problem paper in which the idea of interstellar meeting, held by The Planetary Society, of Doppler shifts of the received wave­ communication at the wavelength of at which I had presented the rationale length (caused by the relative motions neutral hydrogen emission (21 centi­ for a new pair of search systems: a -on the order of some hundreds of meters) was first proposed. He has 100-million-channe1, dual-beam, all-sky kilometers per second-of stars in our continued to be a prime mover in SET!, search of moderate resolution (BETA I), galaxy). They would do this by pre-ad­ delighting even the most experienced to be followed several years later by a justing their transmitting frequency to hands with his sharp insights and sur­ 6-billion-channel, high-resolution compensate for their own motion rela­ prising perspectives. Mike is the direc­ search (BETA II). tive to the remarkable "rest frame of the tor of the Arecibo Observatory in But that was not to be. Instead we universe"-the frame of reference of Puerto Rico; its 1,OOO-foot (300-meter) took off in Phil's rocket ship for a quick the 3-degree-Kelvin radiation diameter makes it the largest radio tour of the galaxy and a look into the left over from the Big telescope on Earth. minds of those other galactic beacon en­ Bang. (These gineers (if any!). Phil wanted to explore fundamen- e were warmly greeted by Phylis something new in SETI this morning, tal WMorrison, who delighted, as always, and he wasn't about to be drawn into in showing new visitors Phil's Swiss­ yet another ho-hum discussion of made funicular- a motor-driven con­ how many frequencies you traption capable of effortlessly lofting can fit onto the head Phil and his wheelchair along the con­ of a pin. tours of a spiral staircase. As received Here's from the factory, its considerable ele­ gance lay hidden. But Phylis has re­ placed the gray metal exterior of its machinery with Plexiglas, thus revealing • ___IIII! its

assumptions of the META search are laid out in the July/Au­ gust 1987 issue of The Planetary; Report.) Instead, Phil suggested, we should how it worry more about the poorly explored went. variables of pulse width (the duration of Phil pulled out a each transmission) and duty cycle (the little rectangle of paper (it average percentage of time that the sig­ looked like the remnant of one of nal is on). And how do we guess rea­ those business reply cards that serve sonable values for these unknowns? mostly to make awkward the process of Easy-the travel time of the message thumbing through magazines), on which sets a natural time scale! he had ecologically interleaved a few Phil then proceeded to carry out a mi­ notes to himself. He began by saying nor subdivision of galactic real estate. Extraterrestrial Mind

Consider only "good" stars, he suggest­ message: about a millennium for a com­ ed-say, spectral type G5, solitary, late munication within our local neighbor­ generation, similar to our Sun. That hood, 10 millennia for a message takes us from an initial stellar popula­ within our slice of the tion of something like 400 billion down galaxy, 100 to a mere billion, give or take a factor of millennia 5. Now, let's stay away from the central for a area of the galaxy, say 10,000 light­ years from the center- it's too vio- lent there. That leaves a flat- tened disk going out from 10,000 light-years to

you play." A related fact about the galaxy: Disembod­ ied hydrogen atoms (free elec- trons and free protons) also cause ra­ dio signals to spread out in frequency, mes­ although for a completely different rea­ sage any­ son. SETI pioneer (and Planetary Soci­ where within the ety advisor) Frank Drake and his stu­ galaxy, and 10 million dent George Helou first looked into this years for communications with in connection with SETI, and they con­ the local group of galaxies. cluded that the galaxy permits very nar­ Now for the deductions about proba­ row frequencies to be sent-as narrow perhaps ble pulse widths and repetition times. as a few thousandths of a hertz, but no 40,000 light­ Whatever creatures may inhabit the narrower. In SETI, narrow is good be­ years-not many galaxy, we all live by the same laws of cause (1) it is distinctive, (2) the re­ stars are out beyond that physics, and we all share the same ceived signal overcomes cosmic noise (think of a 45-rpm record, with galactic geography. It was the universal better for the same transmitted power its large hole in the center). That's the quantum mechanics of the hydrogen and (3) narrow signals from space loqk galactic real estate we're interested in, atom that led Cocconi and Morrison in different from narrow signals generated SETI-wise. 1959 to their brilliant insight that galac­ on Earth, because of the effect of Let's divide this peculiar shape into tic species might well meet at hydrogen's Earth's rotation (the Doppler effect). neighborhoods, so we can have local natural frequency of 1,420,405,751.768 So, the argument goes like this: An town meetings. The galactic thickness vibrations per second, or 1420 mega­ extraterrestrial civilization would not sets the scale, something like 2,000 hertz (still one of META's favorite want to squander the benefits of the light-years. We imagine the disk sliced stomping grounds). Phil wanted to narrowband properties of the galaxy radially into roughly 50 sectors (think of coax another prediction from nature­ by transmitting too short a pulse. How slices of a pie), each further sliced at this time about the complementary short should the pulse be? The recipro­ right angles every 2,000 light-years variable of time. cal of the Drake-Helou bandwidth, (think of eating a slice). Altogether First, the minimum duration of a which works out to a few hundred you've now got about 1,000 neighbor­ pulse. The argument is a bit involved, seconds, if the transmission is at the hoods, each with about a million good but fascinating: It's a curious property hydrogen frequency. suns. Within each neighborhood, a mes­ that the shorter a pulse, the wider its in­ We can get some insight into upper sage takes a millennium or less to reach herent spread of frequency. Numerical­ limits for the pulse width by figuring its destination. ly, the bandwidth (in hertz) is about the that our engineers on the transmitting Looking at our handiwork, we see a reciprocal of the pulse width (in sec­ planet would like to send signals to- . progressive scale of distances, perhaps onds). As my colleague Ed Purcell likes ward each of the million stars in their better appreciated as a progression of to say, "If you playa 1I32nd note on a neighborhood, repeating the perfor­ time scales required for a round-trip tuba, it doesn't much matter which note mance some reasonable number of 5 times (say, 10) in the thousand years it made from silicon-we'll be able to tively unchanging, now has exploded takes for the signal to get there. In do­ omit the large reflecting dish entirely, with Japanese folk tunes. ing that, the transmitter can dwell only instead using the surface of a vast array How could an object such as our sili­ 1,OOO/(lOxl,OOO,OOO) years on each of silicon wafers as the antenna itself, con toy survive for millennia? On Earth target-that's about an hour. connected directly to the underlying sili­ it takes careful engineering to make That's an interesting result for anoth­ con receivers. This is a phased array; something that runs for just a century. er reason: It turns out that the same dis­ able to form multiple simultaneous ra­ Active maintenance would be required. embodied atoms that cause the dio beams. Not only are the intercon­ There must be redundant arrays of an­ Drake-Helou effect also nections part of the silicon, even the tennas, free-floating and self-phasing, give rise to radio power is generated by the silicon itself! replaced as they fail. They would illu­ scintillation, There it is, a dry lake bed tiled with minate the planetary neighborhoods of analo- glistening purple checkerboards of sili­ good stars, perhaps out to 10 astronomi­ con, quietly receiving radio signals from cal units (1 AU is the average distance · ..... a multiplicity of directions. It could from Earth to the Sun), reaching all o ~ ' also be a transmitter, of good suns in the neighborhood in a hu­ course: Sunlight deliv­ man lifetime. If, indeed, this strategy is ..' . ~. · ers a billion being pursued by those other galactic ••. • .-;lJ.. watts beacon engineers, our job is to look at --'. the whole sky continuously, for that , ' ; . ~ .. literally once-in-a-lifetime signal of . ~ . , .•.. '0 ". · ...... • ... unusual strength. : o .~::' . :~, , ..: ...... • A • • o' . .'," ". ;~ ' .: We started scratching . : . ~ ...... • f' . down numbers: . ~ ...

... " . 0 :," ' . 0 Could • • ., 11' ~ ". . " : .. . ' '':~ . .. such ~ ." - " .-. fo .' .' .... . 0, . • . ~ . ~~ .• ; ' ~" ~. .; , :.:". .:' • f '0 . .~ . o. ~ .' . : ... .; . ,".:." . '. gousto ;, . '. ..: the atmo- o•. spheric scintillation ,'." , .", that causes the twinkling of : ..: ' . starlight, and that radio twinkling

has a time scale not of fractions of a :, ' . ' ., . . ~. second (as with starlight), but of a good per '. part of an hour. So an hour-long trans­ square mission (a very long pulse) is likely to kilometer. outlast the fading effect of galactic We liked our futuristic '. ~...... 0 scintillation, and therefore will appear new silicon toy, and quickly be- quite intense for a portion of the time, gan using it. Stepping into the role of .. .. " .. whereas a significantly shorter pulse advanced alien beacon engineers, we might fall victim to a deep fade-out. decided to transmit multiple beams con­ a signal Were we falling prey to faulty rea­ tinuously to known planetary civiliza­ be detectable • soning here? Our argument so far as­ tions-these are messages, for which with the sort of sumed that the extraterrestrials would We use perhaps half our transmitter small-and insensitive-an- send a signal to only one target at a power. The other half we use for con­ tenna that sees the whole sky? (In time. But if they were really advanced, tacting new civilizations, by successive­ an ironic twist of nature not unrelated it would not be difficult for them to ly sending an intermittent beam in their to the fact that pulses short in time are build many transmitting antennas, so directions. These are the pulsed trans­ wide in frequency, big antennas see a they could target many stars at once. missions we invented earlier, visible to small piece of the sky, and vice versa.) At this point I put forth a favorite the radio antennas of primitive civiliza­ "Let's see, roughly 10- 20 watts per idea: Our use of large radio-astronomi­ tions as a flashing beacon, beckoning square meter for 10 dB relative to cal dishes, each with a single receiver for an eventual reply. isotropic. . . mumble, mumble. . able to detect signals from only a single These elegant, metallic purple planes need to illuminate a 10 AU disk at point in the sky at one time, is really a patiently do their electromagnetic range. . . about 1028 square centime­ transient phase in our technological chores, carrying on multiple dialogues ters . . . wow, only 10 kilowatts!" maturation. These antennas are like with established partners, perhaps find­ We fiddled with the numbers a bit to cameras in which we put only a tiny ing a new one once in a hundred millen­ allow for proper motions, and still con­ speck of black-and-white film in the nia. Long periods of sameness, punctu­ cluded it was easy enough, given those focal plane. Our technology is getting ated by occasional newness. Here I handsome purple alien transmitting better: Newer spectrometers cover a mentioned the model of pulsars: many planes. (The idea of beacons strong wider range of wavelengths (color film). similar ones, then a new class-an opti­ enough to be detectable with small an­ And we are beginning to use a few cal pulsar, a fast binary pulsar, a mil­ tennas has been elaborated recently by simultaneous receiving systems (a few lisecond pulsar, or urban pulsar-crowd­ Bob Gray, a Planetary Society member specks of film). ing in a star cluster. Phil's model was and amateur radio astronomer from As our technology improves-and from a different culture: The popular Chicago. See his article, "Isotropic ally 6 we are becoming adept with little things music of Glasgow, for a long time rela- Detectable Interstellar Beacons," Jour. roject META (Megachannel ExtraTerrestrial nomical motions; in addition, it uses the unique signature of a changing PAssay) is The Planetary Society's full-time, radio frequency caused by Earth's rotation to discriminate a genuine whole-sky Search for Extraterrestriallntelli­ cosmic signal from terrestrial interference. The good news is that these gence (SETI), carried out at twin sites: the Har­ algorithms work-the search system has rejected almost entirely the radio vard-Smithsonian 84-foot-diameter steerable mumblings (and bellows) of intelligent life on Earth. The bad news is radio telescope, in Harvard, Massachusetts, obvious-we have made no detections! and the 100-foot-diameter radio telescope of BETA (Billion-channel ExtraTerrestrial Assay) is our planned next step. the Institute of Radioastronomy in La Plata, Close searching in the neighborhood of "magic" frequencies like 1420 near Buenos Aires. It is the most advanced and megahertz hasn 't done the trick. But in those six years technology has ad­ powerful SETI project now operating. vanced nicely, permitting us to cast a much wider electronic net, still with in META's sensitive receivers and sophisticated 8A-million-channel the resou rces of university re search and Planetary Society support. We spectrum analyzer could detect radio signals broadcast intentionally by a plan two steps: BETA I will be a 100-m illion -channel analyzer, hooked to a civilization like ours orbiting any of the nearest thousand Sun-like sta rs . dual -beamu pgrade of the Harvard antenna, that will search the full "water More advanced civilizations-with correspondingly more powerful trans­ hole" (the 300-megahertz band of microwave frequenCies from H to OH- ; mitters-could make themse lves detectable from the farthest corners of see the July/August 1987 Planetary Report) ; BETA II , followi ng five years the galaxy, which contains roughly 400 billion stars in a flattened disk later, will be a 6-billion-channel analyzer that instantaneously covers the 100,000 light-years in diameter. water hole at millihertz ultrahigh resolution . META has now scanned the northern sky several times in the neigh­ -The BETA searches will constitute the fi rst full water-hole search of the borhood of the 1420-megahertz emission frequency of neutral hydrogen, sky, the first dual-beam megachannel receivers and the,l argest spectrum and once near its second harmonic (2840 megahertz). Its companion in analyzers on Earth. We expect the continuation of an independent center of Argentina is now completing the combined full-sky survey, including coor­ excellence, supported by The Planetary Society, to advance the SETI enter­ dinated observations in the equatorial belt seen by both telescopes. prise worldwide, and, through its unique approach, to complement the NASA Since its inauguration six years ago by Steven Spielberg (whose gift to SETI program now getting under way. And-dare we hope?-given that The Planetary Society made its construction possible), META has patient­ each successive project provides us with a receiving system far more capa­ ly scanned the sky for the signature of another intelligent civilization. Its b
e than the last, one of these explorations will someday succeed in making detection algorithms include compensation for the effects of rapid astro- the most monumental discovery in human history; might it be BETA? - PH

Brit. Interplanetary out, it seemed. And we had come full to the soaring communications systems Soc., 43, 532 circle, once again embracing the merits of our morning' s imaginings. of billion-channel receivers. Phil and Exhilarated and exhausted, we drove Phylis couldn't say good-bye without off from the Morrisons' house. Mike ", ; showing us their latest electromag­ said, "What a morning! I could never netic toy, Sony's pocket-size reconstruct that argument!" "But I can," I replied, "because I .... Pro-80 all-band synthe­ sized radio. We took notes!" switched it Paul Horowitz is the inventor and instigator of Project META, the SET! " . program supported by The • ": . Planetary Society. ::...... ", . .: ...... , ",:"

", '.' . .~ .'. "' .. ' . : •... [1990],) .....~. ..:. .. We did a last bit of backseat engineering for our alien culture by noting that they could save a few bucks by go­ ing to a shorter wavelength, where a on, smaller antenna would produce the and found same accurate beam. But as the wave­ the electromag- length gets shorter, the Drake-Helou netic spectrum entirely spreading goes down, and Doppler barren! Earth, it seemed, had shifts go up: The number of receiver recently been showered with the by­ channels increases in proportion to fre­ products of a particularly violent solar quency squared or more! Great, I said­ outburst. All shortwave communica­ another good reason to embark on the tions over the one-tenth of a light-sec­ BETA project I've been dreaming about ond that bound our communicative hori­ for the last year! zon on Earth were blanked out. A fitting Our musings had spun themselves counterpoint, I couldn't help thinking, Illustrations: S, A. Smith hy Clark R. Chapman

ust before high noon last July 11, the Moon crept in front of the Sun. On a beach near San Jose del Cabo, JBaja California, I joined thousands of eclipse chasers who were treated to a rare view of the inner sanctum of the solar system. The Sun's glaring brilliance usually hides not only its own looping prominences and flaring corona, but a vol­ ume of space extending tens of millions of kilometers outward in all directions. As darkness swept across the I landscape, a string of planets could be seen dangling on an invisible celestial thread beneath the gaping black i disk that had replaced the midday Sun. Three of the planets were old friends, familiar to ev­ eryone. Venus, Jupiter and Mars had been playing tag in the evening sky for a couple of months, an unusual plan­ etary alignment that had sparked much public interest. Eclipse totality revealed a fourth object glowing near Jupiter. It was Mercury, the fleeting planet known to the ancients but rarely seen nowadays above the smoggy, skyscrapered skyline of our modern world. Astronomers have long used the brief minutes of to­ tality to study the outer atmosphere of the Sun, to ob­ serve Sun-grazing comets and to hunt for planetoids in- . side Mercury's orbit. But daytime darkness is not really needed to see Mercury. After six minutes of blackout, the Sun was returned to us by the relentless orbital mo­ tion of the Moon, and it sank toward the western hori­ zon. As twilight dimmed, satisfied eclipse watchers gazed westward as the train of planets followed the Sun into the Pacific. Many were surprised by how easy it was to see little Mercury, which-through the accident of geometry­ was located right next to giant Jupiter in the sky. A cou­ ple of times each year, Mercury is just as readily visible against a nearly dark sky for observers favored with transparent skies and a distant horizon. For a world so comparatively close to Earth (about the same distance as Mars), Mercury is poorly studied. Not only have telescopic measurements been hindered by the solar glare, but spacecraft investigations are rendered difficult by the Sun's unrelenting heat. There has been only a single mission to Mercury so far: Mariner 10, which flew past the planet three times after reconnoiter­ ing Venus in the early 1970s. Since then, ground-based astronomers have used several increasingly sensitive observing techniques to study Mercury. For example, analysis of radar echoes from Mercury has yielded maps of the topography on I the planet's unseen side. (Through quirks of orbital geometry, Mariner 10 had observed the same face of Mercury on all three·passes.) As our knowledge of Mer­ cury has grown, appreciation for its significance has broadened, so Mercury is once again a target of inter­ est for planetary mission planners. Mercury is not an easy planet to see, but around the time of the great solar eclipse of 1991, it was visible in the twilight sky. From top to bottom, Venus, the bright star Regulus, Mars, the Moon, Jupiter and Mercury seem to be lined up for A World of Extremes a portrait. Members of the Agrupacio Astronomica de Castelldefels in Spain, who Little Mercury is a world of extremes. Only Pluto is are also Planetary Society members, had traveled to Colombia to experience the eclipse, and there Javier De La Vega photographed this rare planetary alignment smaller, yet Mercury is the densest of the planets (5.43 8 to share with other Society members. Photograph: Javier De La Vega grams per cubic centimeter), reflecting its enormous per- centage of iron. (Actually, Earth is somewhat denser than ulation of asteroid-like bodies residing even closer to the Mercury, but only due to its greater gravitational compres­ Sun than Mercury. sion; Mercury's iron-rich material is denser than the mate­ Mercury has some unique topographic features of its rial of which Earth is made.) With essentially no atmo­ own, notably a planetwide system of huge cliffs, or scarps, sphere, Mercury has no way to transport the Sun's broiling some hundreds of kilometers long. Evidently during the daytime heat to its night side, so it is simultaneously among planet's early history, the little world cooled and shrank, the hottest and coldest planets in the solar system. Al­ causing a crinkling or buckling of its rigid crust. The scarps though Mercury appears geologically "dead," like the record the degree of shortening from which geophysicists Moon, Mariner 10 found that it has a magnetic field, which calculated the planet's cooling history. Scientists have suggests that its deep interior may still be very much alive. been puzzled that Mercury could have cooled and shrunk Superficially, Mercury resembles our own Moon. Its so much and yet maintained--even to the present time­ surface is pockmarked with impact craters, ranging up­ the molten core required to generate the dynamo that gives ward in size to the immense Caloris basin, which is remi­ rise to the planet's magnetic field. niscent of the giant basins on the Moon. Those basins Indeed, Mercury's magnetic field was a surprise from mark the end of the Moon's late heavy bombardment, the start. Experts in planetary magnetism had believed that some 4 billion years ago. They were subsequently flooded rapid spin was necessary for dynamo action. But Mercury with extensive flows of molten rock during a period of ac­ takes 59 days to spin on its axis just once- two-thirds of a tive volcanism. mercurian year, as discovered by ground-based radar in Mercury exhibits wide, flat terrains as well, but they do the earli 1960s. So nobody was really expecting Mariner not share their lunar counterparts' dark color and hence may la's revelation that the planet had an Earth-like, albeit not have originated from the same processes. Mercurian miniature, magnetosphere. craters and intervening plains are subtly different from Theorists also expected that a large, molten interior was those on the Moon. Some differences are ascribed to Mer­ necessary for dynamo action. So they had to go back to cury's greater surface gravity. Possibly some of the craters their modeling. They came up with a new mode for the are from impacts by stray "vulcanoids," a hypothetical pop- creation of a planetary magnetic field involving a thin, not-so-hot spherical shell of fluid material deep within Mercury. This is an example of the cre­ ative interplay between observations and theory that drives science forward. In the last few years, astronomers have been able

Left: Mariner 10, the only spacecraft to visit Mercury thus far, took this oblique view of the heavily , cratered terrain and smoother plains that characterize this planet's face. Near the limb, or apparent edge of the planet, is a scarp, another fea­ ture that is distinctive to Mercury. These features may have formed when the crust buckled as the planet solidified and contracted around its massive iron core. Image: JPUNASA

Inset: Views from a perspective this close to the planet's sur­ face can only be seen through an artist's imagination. Painter Michael Carroll here portrays Discovery Rupes on Mercury. ("Rupes" is the term used in naming scarps on the planet.) Painting: Michael Carroll

9 potential interest to study l emission lines, not only to learn about the behavior of Mercury's small magneto­ sphere, but also to look for possible clues about the composition of Mercury's surface. The usual techniques for learning about the chemical and mineral composition of Mercury are fraught with uncertainty. The measure­ ments are difficult to make, given Mercury's proximity to the Sun's glare, and it is easy to imagine that Mer­ cury's uppermost surface layer---exposed as it is to high-velocity micromete­ Above: Again, an artist can give us a view im­ orite bombardment and the possible from a space­ near-solar environment­ craft. Here the Sun illu­ might not be pristine or minates the region of Mercury seen in the representative of the plan­ image at right. If the et's deeper composition. camera on Mariner 10 Scientists are interested had looked into the Sun-as the artist can in Mercury's composition with impunity-it would because the planet presents have been burned out. us with a potent way of Painting: Don Davis testing theories for the Right: The giant origin of the solar system Caloris basin is partly as a whole. Mercury is, visible in this image after all, an "end-member along the terminator (the boundary between planet"-the innermost night and day). Like object in an array of solid rings formed in still bodies that emerged out water when you drop in a rOCk, circular fea­ of the swirling nebula of tures radiating from its interstellar gas and stardust center testify to the from which our Sun was force of the impact that created this scar 1,300 born. The enormous quan­ kilometers (800 miles) tity of iron within little wide. Image: JPUNASA Mercury, reflected by its high bulk density, has long intrigued cosmochemists. (Mercury's iron core is thought to extend from the planet's center 75 percent to study Mercury's extremely tenuous atmosphere by using of the distance out to its surface!) special spectral lines. Even small quantities of certain ele­ At one time it was thought that planetary compositions ments, including sodium and potassium, emit radiation that were the result of smooth gradations in the chemistry of we can detect spectroscopically as bright, sharp spectral solid material that condensed from the solar nebula at lines. When these lines were discovered in the mid-1980s various distances from the newly forming Sun, ranging in spectra of Mercury, a whole new vista on that world from high-temperature condensates (rocks and metals) near was opened up. Once we thought it had no atmosphere at Mercury to abundant low-temperature condensates (ices) in all. Now we have found that the immensely thin mercurian the outer solar system. In the past decade, however, plane­ atmosphere contains traces of sodium, potassium, oxygen, tary theorists have calculated a picture of the early solar helium and hydrogen. system that is much more chaotic. Using spectroscopic techniques, astronomers can also One scenario for the creation of the planets inside monitor the interactions between Mercury's magnetosphere Jupiter's orbit involves a violent period of collisions of and its surface. For planets with strong magnetic fields, hundreds of worlds roughly the size of the Moon. Iron-rich like Earth and Jupiter, the stream of ionized solar wind par­ Mercury could thus be a metal-rich core of a once larger ticles from the Sun is held far away by a bow shock at the body that suffered an enormous impact with another small boundary of the magnetic field. Mercury's much less pow­ world and was stripped of most of its crustal and mantle erful field is only marginally capable of holding off the so- rocks. .10 lar wind, and the planet lacks an ionosphere. It is of great We really won't know about Mercury's origin, however, I until we can study it in depth and i measure its rocks. It may ulti­ mately prove to be the fmal piece in the puzzle about the processes that. originally shaped our own planet Earth. Mercury may not be as mysterious as Venus, as A World to Explore inviting as Mars Earlier this year, NASA issued a or as majestic as Jupiter, but each 127-page report on the scientific planet has some­ goals of a Mercury orbiter mis­ thing unique to sion. For many years, it had been tell about how our solar system thought that major technological formed and " breakthroughs would be neces­ evolved. This sary before it would be practical mosaic of im­ to take the next step beyond ages taken by Mariner 10 is the Mariner 1O's rather basic studies best portrait so of Mercury. Then Jet Propulsion far of Mercury. Laboratory (JPL) engineer Chen­ Will there be a better one some­ Wan Yen discovered a simple but day? Scientists elegant way to lower a spacecraft and engineers into a near-circular orbit around have studied more ambitious Mercury using conventional missions to this propulsion systems. innermost planet, The trajectory involves multi­ but as yet there are no official ple encounters with Venus and plans to return. with Mercury itself, taking advan­ Image: JPUNASA tage of those planetary gravity fields. Because velocities are so fast in the inner solar system (as a result of the nearby Sun's gravi­ ty), the total mission time is only 3.5 to 5 years. For example, an August 1997 launch would fly by Venus twice and Mercury twice before entering Mercury orbit in July 2002. While JPL engineers were fig­ uring out how to explore Mer­ cury, a diverse group of scientists was expressing interest in the planet. Solar physicists desire a close planetary platform for ob- serving our star's behavior. AstrophysiCists want a Mer­ the Mercury mission, but only in the speCUlative time cury mission to perform additional tests of relativity. (Long frame after the tum of the century. Since then, budgetary ago the advance of Mercury's perihelion, or closest orbital disasters, including NASA's single-minded compulsion to' point to the Sun, provided an early proof of Einstein's theo­ build a space station at all costs, have dimmed hopes for ry of relativity.) sensible space science activities even that far in the fu­ The planetary community has a continuing interest in ture. Mercury for obvious reasons. But it was the space physics Nevertheless, you can go out some early morning or community that took the lead in the latest efforts to plan a just after sunset and spot a gleaming object near the horizon. new mission to Mercury. Over the months you can watch its speedy course through In early 1988, NASA's newly formed Space Physics the zodiac, much like Disneyland's Mad Tea Party ride. Division mandated a JPL engineering study of a Mercury While many are looking to the outer solar system and orbiter mission. Detailed designs were published about a beyond as the next frontier, Mercury traces out the bound­ year ago, followed early this year by the scientific working aries of our solar system's inner frontier and beckons us group's proposals for a complement of instruments that to learn more. would address the most important scientific goals. Spacecraft trip times are short, mission designs are com­ Although the Mercury orbiter mission is both feasible plete, and there is much to learn. Now it is just a matter of and exciting, it is increasingly difficult for NASA to under­ deciding to do it. take new endeavors--even one so widely endorsed and comparatively cheap as this one. Clark R. Chapman was responsible for one of the first maps At a February 1991 strategic planning meeting, NASA's of Mercury's surface to be made following the discovery Planetary Exploration Division tentatively decided to join of the 59-day rotation period. He is our regular News & the Space Physics Division in promoting a new start for Reviews columnist. 11 hen I last reported to The Planetary Society (May/June W1988 Planetary Report), I had the pleasure of describing how my colleague David Balam and I keep track of countless minor planets­ asteroids - in their endless journeys around the Sun. I hope I managed to convey some of the excitement we experience from the hunt. Yet, fun though it is, the question "Why bother?" might be asked. What is the point of measuring in minute detail the exact positions of all these tiny lumps of rock? Indeed, our federal government agency here in Canada put it even more bluntly: "The committee was not convinced that the importance of the accurate measurement of yet more comets and asteroids . .. was suffi­ cient to warrant funding." Just as the rug was thus pulled out from under our feet, The Planetary Society and the National Geographic Society stepped in and saved the day with handsome financial assistance to keep the project going. Thanks!

Designating the Known and the Unknown Asteroid observers talk about numbered and unnumbered asteroids, and the • question "Why bother?" can be asked -and answered-separately for each. The numbered asteroids are the 4,800 or so bodies whose orbits are known with fair precision. The numbers are permanent designations, usually writ­ ten in parentheses, starting with (l) for Ceres, the first asteroid discovered (in 1801), and proceeding to (4789) Sprattia (discovered by Dave Balam as part of this program). By the time this article is printed, there may be more. For the numbered asteroids, the question "Why bother?" takes the · form, "If the orbits of these bodies are known precisely, and their positions can be predicted in advance, what is the point in measuring these easily predicted positions?" Every month, observers who photo­ graph regions of the sky near the eclip­ tic (the plane of our solar system) find This radar "movie" covering 23.5 hours gives us a pollHJn view of asteroid 1989PB as it turns. The white images of asteroids on their plates. Any outline indicates the object's silhouette. Astronomer Steve Ostro and colleagues used the 300-meter that cannot be identified as one of the (1,OOO-foot) Arecibo radio telescope to bounce radar beams .off 1989PB,enabl!ng them to construct the first images of an asteroid. The images revealed that 1989PB consists of two distinct lobes that appear 12 numbered asteroids is, not unnaturally, to be in contact with each other. Eleanor Helin, leader of the Planet-Crossing Asteroid Survey supported by The Planetary Society, discovered this object in August 1989. Image: Steven J. OstrolJPL referred to as an unnumbered asteroid meteorological weathering processes and is given a temporary designation, that constantly alter Earth's face to the year plus two letters, such as obliterate the story of its origin. 199IJX. Many are never seen again, Scientists are tackling these ques­ but often astrometrists (those engaged tions in ingenious ways, using many in positional measurements) will fol­ different types of telescopes and all the low them up until they are identified modem technology they can muster. again and again during subsequent As I write, I have in front of me a passes by Earth. 1,200-page book (Asteroids II, edited If the orbit can then be well enough by R.P. Binzel, T. Gehrels and M.S. established so that the object's future Matthews) made up of 52 papers on path can be predicted, the object will different asteroid studies. The Plane­ join the family of numbered asteroids. tary Society and NASA collaborated For these objects, the question "Why with several other organizations this bother?" takes the form, "Is there any year to organize a seminal conference point in adding more and more bodies on near-Earth asteroids. It is a lively to the roster of permanently numbered subject, involving many different asteroids? Is this not just a purposeless disciplines. make-work project?" Seeing Shape5 and Pattern5 Inten5e and Inde5criuable But there is one common requirement Sati5faction of all these studies, and that is for Honesty compels us to admit that we continuous, up-to-date, comprehensive observe asteroids because of an in­ and accurate astrometric and orbital tense and indescribable·satisfaction computations. obtained from striving to measure as Let's consider the photometry of accurately as possible and seeing our asteroids, which is the measurement of measurements match our careful cal­ their brightnesses and colors. By mea­ culations. We compare the usefulness suring how the brightness varies over of such activities to that of a Mozart time- usually hours- scientists can piano concerto-something that is of tell how fast these bodies are rotating. no practical use but is part of the very Not only that, but they can determine essence of human striving and yearn­ their shapes and whether some parts ing. Yet, when pressed by those who of an asteroid's surface are darker than have to foot the bill, there is no hesita­ others. How bright an asteroid appears tion in describing the purposes, appli­ gives us information about its size and cations and uses of what to us is a how well it reflects sunlight. The highly enjoyable and satisfying study. brightness can be measured through There is, of course, far more to filters of different colors, and astrono­ studying the asteroids than merely mers and geologists can compare the recording their positions. We want observed reflectivities with similar to know their ages, shapes, masses, properties of terrestrial rocks, and rotations and chemical compositions. hence infer the likely mineralogical All these things in tum willhelp us to compositions of the asteroids. answer more fundamental questions, Studies such as these have led to the such as how did the asteroids form, discovery of several different miner­ and what can they tell us about the alogical types, distributed differently history and evolution of the solar in the asteroid belt between Mars and system? Are they derived from a Jupiter. Darker bodies orbit, on aver­ major planet that somehow broke up? age, farther from the Sun than brighter Or did the thousands of tiny bodies ones. This gives us clues to how differ­ never agglomerate into a larger body ent chemical elements separated out as in the first place? they condensed from the contracting The asteroids can probably tell us primeval solar nebula. more about the conditions in the early To measure the brightness of an solar system than can the major plan­ asteroid accurately, the light reflected ets, since they have been unaltered, from it is measured by a sensitive for example, by the geological and photomultiplier through a tiny circular 13 classified into several nesses simultaneously and voila: two types. The darker ones equations in two unknowns, which (which are richer in the can be solved for size and albedo sepa­ lighter chemical ele­ rately. ments) are generally more distant than the Giving Shape to Light brighter and heavier So much for sizes, but have we any ones. But just how many hope of determining the shapes of the of these types are indeed bodies seen only as points of light? distinct? Why are some If asteroids are all spherical, then they types more abundant probably condensed separately from than others? Are the the primordial nebula. But if they are -< types correlated with the irregularly shaped, they might be frag­ dynamic families? ments from awesome collisions between The relations among larger bodies. c the various properties Well, indeed, brave attempts are be­ are so intertwined that, ing made to determine asteroid shapes. even though we now Asteroids rotate and, as they do so, have about 4,800 num­ irregular ones present continuously bered asteroids, we do varying cross sections to the observer. need to measure accu­ The photometrist is able to see its rately and study yet brightness waxing and waning as the more asteroids. It is far asteroid turns over and over. That is, from mere data-gather­ he or she measures the light curve. Radar images can give us some idea of the shape of an asteroid, but our Earth· ing for the sake of it. Now it is true that an asteroid's shape, based technology has a long way to go before we can see a near·Earth asteroid as well as any dark and light patches with the clarity possible with a spacecraft. No missions have yet been sent to any of these bodies that pass so close to our own world, but here artist and scientist Measuring a Point on its surface, determines the light Bill Hartmann gives us a view such as a spacecraft might one day see. Earth and of Light curve. But to deduce asteroid shape its Moon are visible in the background. Painting: William K. Hartmann Have you ever wondered from a light curve proves to be a rather how we know the sizes difficult business. aperture, perhaps just 10 to 20 arcsec­ of asteroids? After all, most of them are There is another way, however, but onds in diameter. To do this, one must so small that they appear only as points it depends on the most precise orbital know exactly where the asteroid is go­ of light even in the largest telescopes. calculations and accurate astrometry ing to be and how fast it is moving. Is a bright asteroid bright because it is possible. We can predict when an aster­ This sounds obvious, and indeed it is big, or merely because it reflects sun­ oid will pass in front of a star and cut so obvious that it is easy to forget just light well? In fact, an asteroid's bright­ off the star's light fo'"f several seconds. how closely the photometrist depends ness depends on its distance (which This is called an occultation and, if it on the astrometrist for the success of we know, thanks to accurate his or her work. astrometry!), its size and its reflectivity (technically ihe Real ana the Unreal known as its albedo). A look at the main-belt asteroids re­ But what happens to the veals some obvious gaps in the distri­ sunlight that an asteroid's bution of their orbits. These are known surface does not reflect? It is as Kirkwood gaps and are thought to be absorbed, and consequently caused by the gravitational influence of warms the asteroid up. The Jupiter. Why are some of these gaps warm asteroid then emits in­ more pronounced than others? How frared radiation, which can many are real and not due to random be detected with special tele­ fluctuations? scopes such as the James Armed with a list of the orbital Clerk Maxwell Telescope in elements (the sizes, shapes and orien­ Hawaii. (Infrared radiation tations of the orbits), scientists have cannot be seen by eye, so an grouped them into several families, asteroid's orbit must be each referred to using an eponymous known with great precision member of each group: For example, to be sure that the telescope we speak of the Cybele or Phocaea is pointing at it.) families. Each family may result from Now the amount of infra­ objects breaking up in the early history red radiation emitted by a of the asteroid belt. But how many are warmed-up asteroid also de­ real families, and how many are chance pends on its size and albedo, groupings? but in a different way from Yet again, if the asteroids' colors, the optical brightness. Astron­ which reflect their compositions, are omers can measure both the 14 measured, we find that they can be optical and infrared bright- • • .. • .. • ., • • • .. • • -.. • • • . is observed by several people scattered .. • .. • • .. • ' across Earth, the asteroid's cross-section /' .. .• can be calculated. (See the March/April .. !lit • ...... 1983 and July/August 1984 Planetary ... . • -. • ., • • .. • Reports.) Then we can use the light • .. • .. curve to detennine the location of light tI .. ••. ' • .... . and dark markings on its surface. •• •••• "'. .- .. .. One must not underestimate the • • • .. difficulty of doing this, but it is aston­ '" " ... - ishing that we can deduce size, shape, '" • • This is the discovery image of 1991JX, seen here as the faint streak against the background of stars. mineralogical composition and the Eleanor Helin found this asteroid over a month before it made its closest approach to Earth, giving Steve locations of surface patches from ob­ Ostro and his radar team time to get into position at the Arecibo Observatory in Puerto Rico. Their obser- servations of a tiny, unresolved speck vations allowed astronomers to pin down 1991JX's orbit with great accuracy. Image: Eleanor HelinlJPL of light! the near-Earth asteroids. of the Jet Propulsion Laboratory, No Time to Wait This poses very special difficulties Eugene and Carolyn Shoemaker of the Much of traditional astronomy is pas­ for observers. Not surprisingly, such United States Geological Survey and sive in that we wait for radiation to objects are usually spotted when they Tom Gehrels of the University of arrive at our telescopes and then we are very close. They then quickly Arizona have discovered scores of analyze it. Some astronomers are tak­ streak across the sky and disappear asteroids that swing close by Earth. ing a more active role. There is in into the depths of the solar system, not These near-Earth asteroids have a Arecibo, Puerto Rico, a huge radio giving anyone much time to carry out scientific interest all their own. Were telescope some thousand feet in diam­ the difficult radar experiments. Astro­ they knocked out of the main belt? eter constructed in a natural hollow metrists must be particularly on their How could that have happened? Are in the terrain. Steven Ostro of the Jet toes to supply good data to the radar they extinct comets? Or are they a Propulsion Laboratory and his col­ observers. different class of object altogether? leagues have been using this telescope One now-famous example is the On the practical side, how often may to bounce radar signals off asteroids. object known as 1989PB (now penna­ we expect one to collide with Earth­ The returning signal is unimaginably nently numbered 4769)--discovered with obvious disastrous consequences? feeble, and it falls off inversely as the by Eleanor Helin, the leader of the Was an asteroid collision responsible fourth power of the distance. This Planet-Crossing Asteroid Survey sup­ for the extinction of the dinosaurs at means that, if you were somehow to ported by The Planetary Society. For­ the end of the Cretaceous period? If double the distance of the asteroid, the tunately, several astrometrists, includ­ one is found to be headed our way, strength of the returning signal would ing Dave and I, found prediscovery what do we propose to do about it? be reduced by a factor of 16! Because images on our photographs and man­ The scenario makes excellent mate­ of this, the technique is best for those aged to do a lot of rapid follow-up rial for science fiction writers, but it is asteroids that pass close by our planet, astrometry. As a result of this frantic by no means an impossible occurrence. activity, the radar experi­ One reason for "accurate measurement ment of Ostro and his col­ of yet more asteroids and comets" is to leagues was a spectacular make a realistic assessment of just how success, revealing that real the danger is. It is possibJe that 1989PB is probably a But most scientists take a more some Earth-born spacecraft have dumbbell-shaped object. positive view of asteroids. We could seen an asteroid Active observation is use them-mine them for minerals and close up-in an not to be limited to radar metals, relieving a little of the burden orbit around Mars. Scientists specu­ bounces. Exploratory space­ from Earth. With their low gravity, little late that Phobos craft visiting the outer solar energy is needed to carry materials and Deimos, Mars' system could take close-up away from them. two tiny moons, looks at asteroids as they Those of us engaged in astrometry are actually aster­ oids captured by travel through the main may seem to be far removed from the the planet's gravi­ belt-(204) Ida and (951) massive engineering technology that ty. The US Viking Gaspra are scheduled for would be needed to bring such dreams orbiters imaged both moons, and visitation by Galileo on its to fruition. But if we were evedo stop one of the Soviet way to the Jupiter system. our humble efforts, these exciting pos­ Phobos craft r~ What will we see? I'll guar­ sibilities would never come to pass. turned images of its namesake. Mars antee there'll be surprises. Yes, we enjoy following the aster­ appears in the But only if we do our oids in their paths, and we do it for our background of this astrometry right! enjoyment alone. Yet the scientific and Phobos image. practical applications of our efforts­ Image: Space Research Institute, Moscow Knowing When to Duck and I have given but a brief sample­ Textbooks tell us that most are endless. We make no apology! asteroids orbit the Sun be­ tween the orbits of Mars and Jeremy Tatum is a professor of Astron­ Jupiter. But in recent years, omy at the University of Victoria in teams led by Eleanor Helin Victoria, British Columbia. 15 The 1991 Solar Eclipse

n The Planetary Society we like to A few weeks before the eclipse, satellite in the right position should think that we view things from a we received a letter from Bruce be able to see. A series of images I different perspective than most Bierman, a Society member from La showing the transit of this shadow people-that is, we see and visualize Mesa, California, asking if any satellites across Earth would have great value, solar system places and phenomena would be making images of Earth he wrote, "in reinforcing in the public from vantage points other than Earth's during the event. As the Moon consciousness an awareness of 'Earth surface. The great solar eclipse of July passed between our planet and the as a planet' as well as an enhanced 11, 1991, is a case in point. Sun, it would cast a shadow that a appreciation and understanding of . I I I I I I I I I I I I I I I I I I I

16 I I I I I I I I I I I I I I I I I I I

--- ~ - ~- From a Different Perspective

an astronomical phenomenon. n in a position to see the Moon's America. The islands of Cuba and Mr. Bierman's idea excited the shadow. A few weeks later, J. De Haiti are visible to the right in these Society's staff. None of us had Waard of the Meteosat Exploitation images. If you look closely, you thought of it. We immediately sent Project sent us this series of images. can see that there is a dark central a fax to Roger Bonnet, Director of Meteosat 3, operating in a spe­ region, the umbra, in the shadow, Space Sciences for the European cial scan mode, tracked the Moon's which is surrounded by a lighter Space Agency, to ask if any of ESA's shadow as it crossed Mexico and penumbra. meteorological satellites would be moved across the top of South Mr. Bierman also contacted the Ir I I I I I I I I I I I I I I I I I I I

17 I I I I I I I I I I I I I I i I I I I United States' National Oceanic and Satellite, Data and Information man for alerting us to the possibility Atmospheric Administration to ask if Service, who sent us the image on of seeing a solar eclipse from the any of its weather satellites would be this page, taken by GOES-7, in which perspective of Earth orbit, and for tracking the eclipse. At his sugges­ the shadow of the eclipse appears making it possible for us to share it tion, we contacted Richard DeRycke off Baja California. with all Planetary Society members. of the National Environmental We would like to thank Mr. Bier- - Charlene M. Anderson International Space Year CelebraleJ Tonwrrow~ ExplorerJ

by StUan LeniJroth

he International Space Year (ISY) of 1992 will Teaching Tomorrow~ ExplorerJ celebrate humanity's fIrst tentative steps away from For the second year in a row, The Planetary Society will T Earth. We have sent robotic spacecraft to the edge co-sponsor the annual convention of the National Science of our planetary system, we have walked on the nearest Teachers Association (NSTA). ISY will see the associa­ planetary body, and we have looked back on our home planet tion's 40th annual meeting, held in Boston from March and seen it, for the fIrst time, from a perspective in space. 26 to 29. A Planetary Society Day on March 27 will feature The year 1992 was chosen for ISY because it marks the several sessions on space science. 500th anniversary of another great voyage of discovery: Bruce Bullock of IS Robotics Corporation will demon­ Columbus' fIrst expedition to the Americas. The year also strate the microrobot Attila. Paul Horowitz of Harvard Uni­ recalls a great exploratory effort only 35 years past: the versity will describe Project META, The Planetary Society's International Geophysical Year (IGY) of 1957. As part of program in the Search for Extraterrestrial Intelligence, and IGY, scientists around the world undertook far-reaching Project BETA, which could greatly expand our search. projects to understand the workings of Earth, and the Soviet Marcia Smith of the Library of Congress will review how Union launched the fIrst artifIcial satellite, Sputnik 1. the turmoil of perestroika has affected Soviet space capabili­ Weaving all these threads together, the organizers of ties. Scientist and artist William K. Hartmann will discuss ISY have chosen as their theme "Mission to Planet Earth." The Planetary Society's new role in the NSTA's upcoming Programs in many nations will demonstrate our ability, education reform project. developed since IGY, to study our planet from space. The Planetary Society is joining the celebration with a series of CelebratwnJ Around the World projects focused not only on terrestrial studies, but also on The International Space Year will provide the theme for missions to other worlds. an educators' conference in Canberra, Australia. Scheduled for July 1992, this international conference is for invited Together to MarJ educators in space science and technology. Thomas O. The launch of Mars Observer in mid-September of 1992 Paine, former NASA Administrator and now a member of will be a centerpiece of ISY. The Planetary Society, working the Society's Board of Directors, will be a featured speaker. closely with the Mars Observer team, is planning a variety [For more information, contact John Nicholas, University of activities at the Kennedy Space Center, including special of Canberra, P.O. Box 1, Belconnen, 2616 Australia; fax tours for Society members and events open to the public. (6) 201-5199.] Tomorrow's planetary explorers, whether human or Other Society educational activities for ISY now in the robotic, will need the imagination and talents of a new gen­ planning stages include educator workshops in Colombia eration of scientists and engineers. To encourage these and Costa Rica, as well as a symposium in Japan. young people of today to join in this endeavor, the Society We will wrap up our International Space Year activities has developed the H. Dudley Wright International Student by celebrating the interwoven themes of ISY: studying our Contest, "Together to Mars." own planet and venturing to new worlds. In December, By 1992 we will have selected 20 winners from around Calileo will swing by Earth on its circuitous route to the world who will receive a prize of $2,500 and a trip to Jupiter. As it did in December 1990 (see the March/April Washington, DC, for the World Space Congress, scheduled 1991 Planetary Report), the spacecraft will tum its instru­ for August 28 to September 6. The winners will be honored ments on Earth. We will once again sponsor encounter during the congress, which will be the fIrst joint meeting of activities in Pasadena, California-the home of both the the International Astronautical Federation and the Interna­ Jet Propulsion Laboratory and The Planetary Society. tional Council of ScientifIc Unions' Committee on Space If you would like more details on these Society events, Research. keep reading The Planetary Report and watch your mailbox.

Planetary RoverJ to Explore Wa-ihington Susan Lendroth is the Manager of Events and Communica­ In Washington during the scientifIc meetings, the Society tionsfor The Planetary Society. will sponsor Rover Expo '92, which is subtitled "An Inter­ national Space Year Exposition of Planetary Robots and Telepresence Technology for Planetary Exploration." We LANETARY SOCIETY MEMBERS can attend the are coordinating our plans with NASA's Space Exploration P, National Science Teachers Association convention in Directorate, the Smithsonian Institution's National Air and Boston at the same discounted rates as NSTA members. Space Museum, and the Robotics Committee of the Ameri­ We will have registration and housing information forms can Institute for Aeronautics and Astronautics. Our members available in November. Please write to NSTA Conven­ and the general public will be treated to demonstrations of tion, The Planetary Society, 65 North Catalina Avenue, the latest advances in exploratory robotics. Pasadena, CA 91106. 19 Questions Answers

In the article "From Siberia to Mars" wouldn't all parts have the same age? longer, has more impact craters than a in the MarchiApril1991 Planetary Re­ -Joubert Malouf, Copperopolis, younger surface. port, the following is stated: "In the California What geologists are really dating, northern hemisphere we find plains however, is an event that erased all the with few impact craters, which indi­ All the planets are continually bombard­ craters that had previously formed on cates that they are younger than 2 bil­ ed with meteorites that form craters on that surface. For example, lava flows lion years." their surfaces. This enables geologists to from a volcano might bury all the im­ How can one part ofMars be younger tell roughly how old a planetary surface pact craters around the volcano. If the than another part? Once a moon or is, since an older surface, having been volcano erupted a billion years ago, we planet forms into the original sphere, exposed to the meteorite bombardment would now see on the lava surface only the impact craters that have accumulated since the eruption. A way from the vol­ cano, we might fmd many more impact craters because the older ones have not been buried by lava. If there are twice as many impact craters on the pre-volcanic surface as on the lavas, we might con­ clude that the older surface is 2 billion years old. As another example, large floods of water on Mars typically destroyed all the impact craters in their paths. A flood can, therefore, be roughly dated by counting the impact craters superim­ posed on the flood channel. The technique gives reliable informa­ tion on the relative ages of surfaces, but it does not give precise information on the absolute age, because we only have rough estimates of the impact rates. Although it works well "on most solid planets, crater-dating does not work well for Earth because the craters are rapidly destroyed by erosion. Compared to other planets, Earth has a very young surface. - MICHAEL H. CARR, United States Geological Survey

Is it possible that the retrograde rota­ tion of Venus [it spins on its axis in the direction opposite to its revolution about the Sun] could be attributed to a collision with a cosmic body? It is theo­ rized that Uranus' tilt is the result of such an event, so couldn't a collision have upended Venus? -Debbie Lamar, Danville, Illinois

Yes, that probably is the right explana­ tion. Currently fashionable (and quite possibly correct) computer model­ going around the Sun with us. FACTINOS ing of the formation of Earth, The energy required to put a giv­ Venus, Mars and Mercury leads to en mass into an initial Earth orbit is the conclusion that the growth of the same regardless of its ultimate Astronomers have discovered that the these planets was marked by giant destination. Because of the strength Moon has a tail. A glowing 15,000-mile impacts. The modeling Indicates of Earth's gravitational fIeld, this is tail of sodium atoms streams from the that many bodies more or less the where most of the energy for such a Moon, blown away from the Sun by the size of the Moon, Mercury and Mars mission would be consumed. Only a solar wind-the constant stream of parti­ formed fIrst, and that the larger ter­ little more energy would be required cles flowing from the Sun. The Moon's restrial planets seen today resulted to go on to the Moon from there be­ tail is not visible to the naked eye, but from the collision of many of these cause the Moon is simply in a high­ instruments can see the faint orange glow smaller, but still planet-sized, bodies. er Earth orbit. The amount of energy of sodium. This leads to a natural explana­ required to go beyond the Moon is "The scientifIc community still isn't tion of the origin of the Moon by also relatively small. sure of the source of these sodium material from Earth "splashing" into It's the arrival at the asteroid ver­ atoms," said Michael Mendillo of Boston orbit about the planet, followed by sus the Moon that is different. Al­ University, one of the tail's discoverers. the gravitational "clumping" of this though it is less massive than Earth, It is probable, he said, that sodium atoms debris to form the Moon. It may also the Moon still has a large gravita­ are being blasted loose as rocks on the explain why Mercury has a large tional effect. To soft-land on the Moon's surface are hit by tiny meteorites. iron-rich core, but only a relatively Moon, this gravity must be coun­ Others argue that sodium is liberated by thin layer of rocky material sur­ tered with energy- for example, by solar wind particles or by photons of rounding the core. These same com­ fIring retrorockets. Then it must be sunlight. puter calculations show that giant overcome again when leaving. The - from the Los Angeles Times impacts can almost completely re­ gravitational effect of a small aster­ move rocky mantles from small oid, say, 1 kilometer in diameter, is planets like Mercury. negligible from an energy stand­ Magellan recently found a volcanic flow These large impacts are certain to point, so that with carefully chosen on Venus that suggests the planet has be at least somewhat off center and arrival and departure times, energy explosive eruptions like those at Mount will, therefore, cause the planet that consumption is not significant. Pinatubo in the Philippines and Mount is struck to spin one way or the oth­ - ELEANOR HELIN, Jet Propul­ Unzen in Japan. A petal-shaped volcanic er. One spin direction is about as sion Laboratory flow discovered on a highly fractured probable as the other, so it may be portion of Venus' landscape may have just an accident that Venus' spin is Why isn't the energy of the Earth­ been deposited by "an eruption like those retrograde and that of the other three Moon system routinely used as a that are currently happening in Japan and terrestrial planets is prograde. Early gravity assist for planetary explo­ the Philippines," said James Head of in its history, Venus was probably ration? Brown University. spinning quite rapidly in this retro­ -Joel MacAu sian, Nashua, New Venus has tens of thousands of volca­ grade manner, but solar tidal forces Hampshire noes, and many scientists think it's likely have decreased its rotation to the that some are erupting now, though they slow rate of 243 Earth-days ob­ Gravity assists using the Earth­ haven't yet caught one in the act. served today. Moon system are becoming more -from the Associated Press - GEORGE W . WETHERILL, commonplace. Galileo used Earth Carnegie Institution o/Washington gravity assists to help it on its way to Jupiter. The Cassini mission to Dr. Andrew G. Lyne and colleagues at In the January/February 1991 issue Saturn and Titan will use this tech­ the Nuffteld Radio Astronomy Laborato­ of The Planetary Report, Eleanor nique as well. ries at the University of Manchester in Helin states in "Eureka! The Re­ The disadvantages of using an England say they've discovered a planet covery of 1982DB" that this near­ Earth-Moon gravity assist are the around a distant star. If their report is Earth asteroid is "even easier to associated time and navigation con­ confrrmed, this would be the fIrst estab­ reach than the Moon." How can straints-for example, trajectories lished detection of a planet beyond our this be possible? must be longer and must be precise­ solar system. They say the object orbits a -Dennis W. McDonnell, Clinton, ly aligned in terms of the positions pulsar, the spinning remnant of a star that Michigan of celestial bodies. collapsed after a violent explosion. As for a Moon-only gravity assist The astronomers reported that they'd The accessibility of an asteroid is for an interplanetary trajectory, the observed fluctuations in radio signals measured by the amount of energy amount of extra energy derived is from the star and that they believe the that would be required for us to small and rarely useful. The disad­ fluctuations are caused by the gravita­ rendezvous with it; in the case of vantages of having to precisely time tional effects of an orbiting companion the Moon, to land on it. The energy your departure trajectory from Earth about 10 times the mass of Earth. They required varies with the orbit of would outw~igh the gain in energy said the object appears to be as close to each asteroid and its position rela­ from the assist. Even Mars, over the pulsar as Venus is to the Sun. The tive to Earth at the time of launch. nine times the mass of the Moon, pulsar itself is about 30,000 light-years The accessible asteroid mission can supply very little extra energy from our solar system toward the center candidate will have orbital charac­ from this technique. of the Milky Way. teristics comparable with those of -LOUIS FRIEDMAN, Executive - from John Noble Wilford in Earth- in other words, it will be Director The New York Times 21 s we go to press, the United States sion adds to concerns about equipment PASADENA-The idea of exploring ACongress is still in its August re­ reliability. Accidents do happen. Dur­ planets with small, specialized space­ cess, and the Conference Committee ing the 1988 Phobos mission, both craft, rather than the school-bus-sized, has not yet worked out the details of spacecraft were lost. This next genera­ instrument-bedecked platforms of NASA's 1992 budget. As we reported tion of Mars spacecraft are derivatives recent design. has been discussed for in our July/August issue, the fates of of the basic Phobos design. During the years. But while the funding for mega­ several planetary missions, the Earth meeting, a team of ballistics experts projects was available, "microspace­ Observing System and new launch was assigned the task: of improving the craft" were regarded as offering too vehicle development-among other mission trajectory and timeline to little scientific payback, and so were programs-are hanging in the bal­ maximize the data return and the prob­ given low priority. ance. We will give you final budgetary ability of success for the balloon. If this same mentality had been used details and analyze their effects in the Meeting participants discussed an· to build computer cbips, we would not next issue of The Planetary Report. other concern at length: the steriliza­ have desktop computers today. Indeed, tion of the entire descent module and the miniaturization of electronics, me­ MOSCOW-In July, the French-So­ its contents. Guidelines laid out by chanical hardware and propulsion sys­ viet Mars mission design team met at the Committee on Space Research tems makes it possible today to build the Babakin Center to discuss progress (COSPAR) of the International Coun­ small spacecraft that are more capable on the Mars '94 and Mars '96 proj­ cil of Scientific Unions require that the than some of the giants of yesterday. It ects. The Planetary Society participat­ chance of a single earthly microbe ar­ is true that a small satellite cannot car­ ed in the meeting to report on our riving on Mars should be 1 in 10,000. ry as many or as powerful instruments SNAKE guide-rope testing and bal­ This is an enormous technical chal­ as a large one. But a "microcraft" loon system analysis. We also wanted lenge. Sterilization USing heat or fumi- could be simple, built quickly and at an update for our members and bal­ , gation with radioactive gas is possible, much lower cost. In any case, launch loon team on the status of the Soviet , but either method could damage deli­ vehicles to propel US space vebicles to program. cate or sensitive spacecraft parts. Mars remain a big problem. Smaller Discussions centered on changes to The Planetary Society agreed to act spacecraft require smaller-and cheaper the original Mars' 94 plan due to tech­ as liaison among the international sci­ -rockets. nical problems with the orbiter and de­ entific bodies involved in tbis question NASA hopes to take a step in tbis scent module. and financial difficulties and to provide engineering support to direction with its Discovery Program, within the Soviet space program. help solve the spacecraft sterilization in which a spacecraft must be small, Project managers confirmed the de­ problem. simple, and cost less than $150 mil­ cision to split the mission into two The team from France's Centre Na­ lion. Several mission scenarios that parts, an orbiter to launch in 1994 and tional d'Etudes Spatiales reported on might fit into this program were pre­ an orbiter and descent module to the latest flight tests of the full-scale sented at the recent International launch in 1996. The Mars Balloon, Mars Balloon. They have launched Conference on Near-Earth Asteroids, which the Society has been working several balloons from Norway to gath­ co-sponsored by the Society and on since 1987, will fly on the Mars '96 er data during long flights in Mars-like NASA. mission, along with small meteorologi­ conditions. They collected some data, The Planetary Society is investigat­ cal stations and a minirover. but need to conduct further tests to ing even greater steps toward smaller The Mars team is concerned about confirm the flightworthiness of the missions. We've invited the world's the potential loss of the Mars Observer balloon design. experts on small satellites to a Society relay due to the delay in the mission. Tests of the latest rover design were workshop in Pasadena on September This device would·relay data from the also discussed, induding The Plane­ 23 and 24. We will address subjects Mars Balloon back to Earth. NASA's tary Society'S role in them. As we go like small spacecraft, launch ehicle Mars Observer will launch in 1992, to press, Society Executive Director possibilities, microrovers and small and there are no guarantees that it will Lou Friedman, the Society'S Mars penetrating probes of planetary sur­ still be working when the balloon and team leader Bud Schurmeier, project faces. rover reach the planet in 1997. The consultant Tom Heinsheimer and Jet The current budgetary situation in Soviet Mars '96 orbiter is capable of Propulsion Laboratory engineer Roger the United States makes it likely that relaying the data to Earth, but at a Bourke are in Kamchatka, Siberia, for NASA ~ ill send no spacecraft to the much slower rate. the tests. We are now organizing a planets in the decade following the Another problem in delaying the new round of rover tests to be held in Mars Observer launch in 1992. That launch until 1996 is that the spacecraft California's Mojave Desert next is, none will go unless we find differ­ will arrive during the martian dust. spring. ent and innovative ways to do it. At storm season. It might have to park in We will keep you informed of fur­ The Planetary Society we are seekers orbit for up to six months before the ther developments. -Tom Hein­ after innovation. -George Powell, dust clears. Any extension of the mis- sheimer, Mars Team Consultant MicrQspacecraft Study Leader insurance beneficiary, is with or knowledge of free cy makers will be coming to­ PRESIDENTIAL AWARDS available. Please write me at fall) to participate in their gether for this special Inter­ For the fourth year in a row, the address below if you pilot run this fall. national Space Year event. The Planetary Society will would like more information. The project will enable stu­ Most of the Congress' ses­ participate in the Presidential -Lu Coffing, Financial dent design teams in schools sions will be technical, but A wards for Excellence in Manager across the United States, there will be exhibits for the Science and Mathematics communicating via electronic public and other special Teaching. Each of 216 teach­ WE LOVE A MYSTERY networking, to focus on the events- including a Rover ers selected from elemen­ But not when our members redesign of everyday objects Expo sponsored by The Plan­ tary, junior high and sec­ are missing. Membership Co­ to function in a zero-g envi­ etary Society. ondary schools throughout ordinator Sue Pratt regularly ronment. If you are interested in the United States will receive receives membership renewal For information, contact helping us with the contest a one-year membership in the checks and money orders James A. Levin, University winners and the special Soci­ Society. -Susan Lendroth, without names on them, as of Illinois at Urbana-Cham­ ety events, please write me at Manager of Events and Com­ well as gift memberships paign, 210 Education Build­ our offices. munications without the recipient's name ing, 1310 South Sixth Street, -Susan Lendroth and address. And Sales Su­ Champaign, IL 61820-6990; CONTEST WINNER ATTENDS pervisor Cosma Norton has a fax 217-244-7620. - Louis EVENTS CALENDAR AVAILABLE MARS SYMPOSIUM bulging folder of orders that Friedman, Executive Director The Society'S worldwide Vol­ Eric Choi, winner of The she cannot fill because of unteer Network organizes a Planetary Society's 1991 similar missing information. HELP WANTED FOR great variety of events every Mars Institute Student Con­ Both have become adept at WORLD SPACE CONGRESS year. If you would like to test, was the Society's guest tracking down the informa­ We are looking for Washing­ receive a copy of the network at the "Mars Exploration: tion they need, but unsolved ton, DC, area members who events calendar, please write Past, Present and Future" cases remain. can help us organize the me at the Society'S offices. symposium, held in Williams­ Most often overlooked are grand prize for 20 students - Carlos f. Populus burg, Virginia, July 17 to 19. the little things, like the last from around the world who He also received an award of four digits on your credit will be selected as winners of $500. Eric's research paper card, the expiration date, a our "Together to Mars" Inter­ on designs for power systems signature. It's especially im­ national Student Contest, to be used for a human Mars portant to put your name and sponsored by the H. Dudley base in the next century was membership number on mon­ Wright Foundation of Gene­ KEEP IN TOUCH selected from a very impres­ ey orders and on checks that va, Switzerland. sive field of entries. are not personalized, such as The 20 winners and their Our mailing address: - Carlos 1. Populus, Volun ­ cashier's and organization chaperones will be going to The Planetary Society teer Coordinator checks. Washington to attend the 65 N. Catalina Avenue Please take a moment to World Space Congress (Au­ Pasadena, CA 91106 MEMBERS' BEQUESTS check for missing informa­ gust 28 to September 6,1992). We would like to honor Min­ tion before you seal that en­ They will need housing, Califor an updated neUe Luckner of Mill Val­ velope. Also, be sure to in­ meals, transportation and events calendar: ley, California, and Marlow clude your fax number when guides to Washington sites (818) 793-4328 Samuelson of West Des you fax an order to us. of interest. With their hosts, east of the Mississippi Moines, Iowa, two members - Cindy falife, Membership they will be attending a spe­ (818) 793-4294 whose support for The Plane­ Services Manager cial Planetary Society recep­ west of the Mississippi tary. Society has been contin­ tion and awards ceremony. ued after their deaths through A GATHERING OF The World Space Congress General calls: very generous bequests. ZERO-G DESIGNERS is a combined meeting of the (818) 793-5100 A pamphlet on planned Organizers of the University In ternational Astronautical giving, which discusses how of Illinois Zero-g World De­ Federation and the Commit­ Sales calls ONLY: members may make estate sign Project are looking for tee on Space Research of the (818) 793-1675 donations to the Society, ei­ schools and for interested in­ International Council of Sci­ ther by direct bequest or by dividuals (especially those entific Unions. Leading space naming the Society as a life- having firsthand experience scientists, engineers and poli- 23 CALORIS IMPACT- Our solar system has a history of violence. One dramatic piece of evidence of this is the Caloris basin on Mercury. In this painting, Rick Sternbach illustrates the explosive confrontation between planet and impac­ tor that formed the basin, which is over 1,300 kilo­ meters (800 miles) across. Our own neighborhood is not safe from such violent events: The Imbrium basin on our Moon looks very much like Caloris, and was created in the same way.

Veteran space artist Rick Sternbach is a founding , member of the International t ! Association of Astronomical ! Artists. He works as the ) senior illustrator and a t technical consultant on Star Trek: The Next Generation. I I I

t

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