A Publication of THE PLANET: SOCIETY

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Board of Directors FROM THE CARL SAGAN BRUCE MURRAY President Vice President Director. Laboratory tor Planetary Professor of Planetary Studies. Cornell University Science. California Institute of TechnoJogy LOUIS FRIEDMAN Executive Director JOSEPH RYAN Q'Mefveny & Myers MICHAEL COLLI NS Apollo 11 astronaut STEVEN SPIELBERG he political and economic state of the Reagan calls for the international explo­ director and producer THOMAS O. PAINE Tworld is in flux, making the future of ration of space, former Administrator, NASA; HENRY J. TANNER Chairman, National financial consultant planetary exploration uncertain. Still, the Page 18-News & Reviews- Triton, Commission on Space discoveries go on, as you'll read in this Neptune's largest satellite, is the topic of Board of Advisors issue. our faithful columnist. DIANE ACKERMAN JOHN M. LOGSDON Page 3-Members' Dialogue-Clark Page 20-Questions & Answers-What poet and author g:~~o;'~~:fu~;g~C(;~~;:;~~ , ISAAC ASIMOV Chapman's recent critique of exaggerated would happen if a planet blew up? Could author HANS MARK Chancellor, planetary images released by NASA hit an asteroid be used as a spacecraft? What RICHARD BERENDZEN University of Texas System educator and astrophysicist home with a lot of our members, and many three planets rotate backwards? Read this JAMES MICHENER JACOUES BLAMONT author wrote to support his views, (One member, column to find the answers, Chief Scientist. Centre National d'Etudes Spatiales, MARVIN MINSKY David Morrison, in a letter published in the -Charlene M, Anderson France Toshiba Professor of Media Arts and Sciences, Massachusetts American Geophysical Union's Eos, has RAY BRADBURY Institute of Technology poet and author even called for the creation of a "Flat ARTHU R C. CLARKE PH ILIP MORRISON Institute Professor, Massachusetts Venus Society,") author Institute of Technology SPECIAL ANNOUNCEMENT: CORN ELI S DE JAGER Page 4-Titan's Greenhouse and Anti­ PAUL NEWMAN Professor of Space Research, Cassini Crisis Updates The Astronomiea/lnstitute at actor greenhouse Effects-A decade after it Utrecht, the Netherlands JUN NI SH IM URA flew by Titan, Voyager 1 still has some­ As we go to press, the future of FRANK DRAKE Director-General, Institute of Space Professor of Astronomy and and Astronautical Sciences, Japan thing to teach us about this intriguing Cassini, the NASA/European Space Astrophysics, University of California, Santa Cruz BERNARD M. OLIVER moon of Saturn's. Using Voyager data and Chief, SET! Program. Agency mission to investigate Saturn LEE A. DUBRIDGE NASNAmes Research Center computer models, a team of researchers former presidential and its large moon, Titan, is in doubt. science advisor SALLY RIDE Director, California Space Institute, has discovered an anti greenhouse effect There is a possibility that the US JOHN GARDNER University of Califomia, San Diego, founder, Common Cause and former astronaut operating in its atmosphere. Congress will cancel it, and so end the MARC GARNEAU ROALD Z. SAGDEEV Page 8-Through the Fuzzy Boundary: development of scientifically ambitious Canadian astronaut former Director, Institute for Space Research, A New Route to the Moon-"Innovation" and mid-sized robotic missions for the GEORGIY GOLITSYN Academy of Sciences of the USSR Institute of Atmospheric Physics, is a word so casually used in the modem foreseeable future. Academy of Sciences of the USSR HARRI SON H. SCHMID former US Senator, New Mexico, world that its meaning has been diluted. The Planetary Society has taken a THEODORE M. HESBURGH and Apollo 17 astronaut President Emeritus, Really new concepts can be lost in a bliz­ stand for Cassini, and, through the grass­ University of Notre Dame S. ROSS TAYLOR SH IRLEY M. HUFSTEDLER Professorial Fellow, Australian zard of buzzwords and half-baked ideas. roots campaign of our members and the National University, Canberra educator and jurist One recent innovation in celestial mechan­ congressional testimony of our officers, GARRY E. HUNT LEWIS THOMAS space scientist, Chancellor, Memorial Sloan United Kingdom Kettering Cancer Center ics, however, represents a true advance in we are trying to help save the mission, SERGEI KAPITSA JAMES VAN ALLEN space traveL The discoverer of fuzzy As a bimonthly publication, it's im­ Institute for Physical Problems, Professor of Physics, Academy of Sciences of the USSR University of Iowa boundaries describes how this concept possible for The Planetary Report to could make spacecraft missions more af­ keep you up to date on a political situa­ The Planetary Report (ISSN 0736--3680) is published six times yearly at the editorial offices 01 The Planetary Society, 65 North Catalina Avenue, fordable. tion that can change day by day. To Pasadena, CA 9 11 06, (818) 793-5100. II is available to members of The Planetary Society. Annual dues in the US or Canada are $25 US dollars Page ll-Keeping an Eye on Earth: Re­ remedy this, the Society is instituting or $30 Canadian. Dues outside the US or Canada are $35 (US). mote Sensing in Russia- The same tech­ Editor, CHARLENE M. ANDERSON a new service for the duration of this Technical Editor, JAMES D . BURKE nology that ushered in the Space Age and crisis: Assistant Editor, DONNA ESCANDON STEVENS Copy Editor, GLORIA JOYCE enabled spacecraft to explore the planets is You can receive updates on the status Production Editor, MITCHELL BIRD .Art Director, BARBARA S. SMITH also being used to study our home world. of Cassini by calling our events calen­

Viewpoints expressed in columns or editorials are those of the authors and The former Soviet Union was a leader in dar telephone line: (818) 793-4294, do not necessarily represent positions of The Planetary Society. its officers or advisors. © 1992 by The Planetary Society. remote sensing of Earth, and we report As with anything involving a govern­ 'In Canada. Second Class Mail Registration Number 9567 here on its satellite capabilities, ment program, things may change Page 16-Society Notes-The latest So­ hourly or remain stable for weeks. We COVER: Remote sensing is possibly the most powerful scientific tool to mature during the Space Age, These ciety activities are detailed for you here. will update the recorded message as we false-color images of the Moon were compiled from data Page 17-World Watch-Planetary ex­ receive news of developments, returned byGalileo during its 1990 Earth-Moon encounter and later superimposed over an airbrushed map, The ploration by the United States is seriously We hope you will let your represen­ ways surface materials, such as soils, reflect light can tell threatened: The Cassini mission to Saturn tatives and senators know that you sup­ us about their composition, Here the different colors indi­ may be canceled by Congress. But France port Cassini. If we lose this mission, the cate different reflectivities and composition, For example, green and yellow indicate iron- and magnesium-rich reaffirms its commitment to help the Rus­ US planetary program may wither away. minerals, Image: United States Geological Survey sian Mars missions, and former President NEWS BRIEFS

Michael Griffm, NASA's associate As administrators of a membership organization, The Planetary Society's Directors and administrator for exploration, told staff care about and are influenced by our members' opinions, suggestions and ideas Congress recently that the space about the future of the space program and of our Society. We encourage members to write agency could send humans back to us and create a dialogue on topics such as a space station, a lunar outpost, the exploration of Mars and the search for extraterrestrial life. the Moon and on to Mars for about Send your letters to: Members' Dialogue, The Planetary Society, 65 N. Catalina Avenue, one-fifth of the huge cost it esti­ Pasadena, CA 91106. mated less than three years ago. During testimony before the House Science, Space and Technol­ ogy space subcommittee, the top Three cheers for Clark Chapman's critique of the false colors used in just about all publicly exploration official rejected the old released NASA planet photos! [See the January/February 1992 issue of The Planetary Re­ $500 billion price tag for the 30- port.] It's about time someone pointed out that 10 is not the same colors as a pizza with dou­ year project that came out of a ble cheese and pepperoni, that the distorted surface of Venus isn't Day-Glo orange and that 1989 NASA study, and agreed to even the Mars we've come to know and love is not a brilliant crimson and peach. Aside from place the effort under tight funding a past issue of Sky & Telescope that had an article showing the "true" colors of the planets, I caps. have seen no other refutations in the news media about all the fake colors that are passing NASA can do the projects for for reality. "on the order of $100 billion," but Would it be possible in some future issue of The Planetary Report to show us what all the detailed numbers will not be ready planets (and at least some of the moons) in our solar system really look like, shorn of false for at least two years, Griffin said. ultraviolet purples (a la Venus and Saturn) and computer enhancement? Is Neptune as blue The hearing marked the start of a as Newsweek crowed in its 1989 cover story on Voyager 2 and "The Blue Planet"? And contentious battle in Congress over what color is Mars, anyway? boosting space agency funding for -JOHN ROUNDS, Hoboken, New Jersey lunar and Mars missions. -from Space News In his News & Reviews. column in the January/February 1992 Planetary Report, Clark R. Chapman is right on the mark in pointing out that the common use of exaggerated and false color in space probe images of other worlds, while useful for specific technical purposes, in . the absence of proper labeling often misleads the public. It has sometimes even colored the In February, after hearing of new impressions of scientists themselves as to how these worlds really look to the human eye. evidence that Earth's ozone layer In his reference to "Saturn's nearly colorless rings," however, he is well off the mark. may be weakening over parts of In 1944 I was privileged to view Saturn through the 36-inch refractor at Lick Observatory. the United States, President Bush The image of Saturn I saw then, with its rings tilted at a good angle from Earth and extend­ directed American manufacturers ing across the entire field of view, has never left me. Especially awe-inspiring was the softly to stop virtually all production of glowing deep violet of the inner, dark C-ring, contrasting dramatically with the brilliant yel­ ozone-destroying chemicals by the low of the adjacent B-ring region and the duskier, orangy outer A-ring. To me the C-ring, end of 1995, ratherthan by 2000. sometimes called the crepe ring, was the crowning glory of the entire ring system. Yet no -from Keith Schneider in The telescopic photos and no Voyager images I have seen (except, naturally, the false-color New York Times images) show the crepe ring as anything other than a dark gray color. Some may suggest that the intensity of color I describe is a result of memory enhance­ ment, but it was so vivid that I think no such enhancement is possible. It was very much like the deeply glowing violet seen at the shortwave end of a solar spectrum thrown by a prism James G. Anderson, Harvard chem­ against the white wall of a darkened room. It is conceivable too that the yellows and oranges istry professor and mission scientist might have been enhanced somewhat by Earth's atmosphere, but as noted in Chapman's arti­ for NASA's Airborne Arctic Strato­ cle, our ground-based view of the Moon when high in the sky shows little discernible differ­ spheric Experiment-2, an aerial ence from the hue our astronauts have seen from space or on the Moon itself. I believe that assault on the ozone problem, says truly deep colors like the C-ring's violet would be even less altered in viewing through that the greatest restraint on sci­ Earth's atmosphere. ence in studying ozone loss "is the While there are certainly many examples of unlabeled color exaggeration and the use of inability to get deep into the higher false colors in the published images we have been treated to, in at least some cases there is a altitudes of the atmosphere where . problem in the other direction, in which vividness of color in space objects has been grossly the chemistry is happening, partic­ . understated or even entirely uncaptured. ularly over polar regions." ~LEE G. MADLAND, Ridgecrest, California This zone, too high for most aircraft to reach and too low for I wish to express my appreciation to the Society for the diversity of relevant information thorough satellite observations provided through The Planetary Report, while maintaining the integrity of basic goals. This from space, is prompting the devel­ publication is the only one that I study from cover to cover upon receipt and then wish there opment of a new class of robot air­ were more. planes to monitor ozone depletion After noting the various references in the November/December 1991 issue to the potential and global warming. availability of the "Soviet" space program equipment, I wondered if there might not be an Now six companies are propos­ opportunity to try a different approach. Let us consider the possibility of having the United ing aircraft designed to work at (continued on page 19) (continued on page 19) 3 hose of us engaged in comparative planetary science deeply into the greenhouse effect. As we did, we discov­ have traditionally focused on the three "terrestrial" ered that Titan had an anti greenhouse effect as well. planets: Venus, Earth and Mars. The outer solar We knew about Titan's atmosphere from early ground­ system, dominated as it is by the giant planets, Jupiter, based spectrographic studies, which detected methane Saturn, Uranus and Neptune, seemed to hold nothing (CH4), a molecule that may have played a cnicial role in Earth-like at all. the origin of life on Earth. From Voyager, we got a detailed But when Voyager 1 flew by Titan, the largest natural look. We learned that Titan's atmosphere, like Earth's, is satellite of the planet Saturn, more than a decade ago, we predominantly nitrogen (N2). No other known objects in learned a lot about this distant world. We discovered this the solar system have such an atmosphere. moon to be, in some unexpected ways, similar to Earth. Moreover, Titan's surface pressure is only 50 percent Titan is the only known moon in the solar system that has greater than that of Earth. By contrast, our nearest celestial a significant atmosphere, as Earth has. We have been study­ neighbors, Venus and Mars, have atmospheric pressures ing this atmosphere, using a computer program that can that are about a hundred times higher and a hundred times simulate it. Because we wanted to know what the tempera­ lower, respectively, than Earth's. It would be much easier ture of Titan would be under conditions different from those to pressurize a space suit for an explorer on Titan than to of today, we began to perform a series of "what-if' experi­ outfit a human to survive on Venus or Mars. ments. It is one of the joys of computer modeling that such The second most abundant gas on Titan is methane, and "experiments" can be carried out on an entire planet. A here the similarity with the present-day Earth breaks down. vexation is that sometimes the results can be surprising­ The nitrogen and methane in Titan's atmosphere react under just as they can be in regular experiments. the influence of sunlight and high-energy particles to form In our results, we found that under some conditions­ hydrogen (H2), which escapes to space, and complex pressures about half the present value-Titan was surpris­ organic molecules. This process leads ultimately to solid ingly cold. Colder, in fact, than it would be without any organic material that forms a high-altitude haze layer. Like 4 atmosphere at all. To understand this we had to delve the smog that obscures the Los Angeles skyline on a hot On November 12, 1980, Voyager 1 flew close by Titan and from a range of 22,000 kilometers (13,700 miles) took this image of the organic haze layer surrounding the moon. The colors in this image are false and are used to show details that are not readily apparent in true colors. Image: JPUNASA

summer day, this haze layer effectively hides Titan's surface. Since we can't see that surface, we can only speculate as to its nature. This satellite's surface is intensely cold-minus 178 de­ grees Celsius (minus 288 degrees Fahrenheit), compared to the more salubrious 15 degrees Celsius (59 degrees Fahren­ heit) average for Earth. Because of this cold, methane and

other light organic molecules (primarily ethane, C2H6), which would be gases on Earth, exist on Titan's surface as liquids. However, at these cold temperatures, water is as hard as rock- a serious problem for life (see box on page 6). Over the more than 4.5 billion years since Titan formed, we would have expected that simple hydrocarbons like methane would be. continuously recombining into heavier or­ ganic molecules, which would collect on the surface as solids and liquids; this process would deplete the atmosphere of methane. But some source is resupplying the atmospheric methane. A large reservoir-an ocean- of methane has been suggested as this source by Jonathan Lunine and his colleagues. If the methane is not abundant enough, there may not be an ocean but many lakes: Titan, land of 10,000 lakes.

Seen from 2.3 million kilome­ ters (1.4 million miles) away, Titan looks like a fuzzy orange tennis ball. Its thick, mostly nitrogen atmosphere, tinted orange by organic compounds, completely obscures the sur­ face. It looks to be a dull place. But if you look closely at this image, taken by Voyager 2 in August 1981, you can see some faint atmospheric fea­ tures. A band of dark clouds circles its north polar region. Near the equator is a band that divides the atmosphere into hemispheres; the southern hemisphere appears lighter than the northern one. Faintly visible near the limb (apparent edge) of the moon is a haze layer of organic particles-the source of the antigreenhouse effect on Titan. Image: JPUNASA

5 ~----~---,-, -----_..--__ .-...... _---_.--_......

for present-day life. This atmosphere life. At the 1991 meeting of the Division ntanandthc would have been similar to the one we for Planetary Sciences of the American l frod on Titan today. Over billions of years, Astronomical Society, Stanley Miller and Prablotlc Earth some of these simple molecules would Chris Chyba, a young proponent of the he production of organics on Titan­ have slowly evolved into more complex new view, debated before a packed house Tby processes that don't involve life­ molecules, including amino acids. At of scientists. However this debate is re­ forms-naturally suggests a comparison to some point, these large chemical com­ solved, Titan's chemistry may still provide Earth before life began. The study of Titan pounds formed self-replicating units, clues to the origin of life. may help us refine theories that life on which we would classify as life. Since Miller's initial work, researchers Earth began with a similar production of However, recent evidence suggests that have repeated organic synthesis experi­ organic molecules. Earth's early atmosphere was instead rich ments many times, including simulations These theories are based on the classic in carbon dioxide (C02), water and nitro­ in which the gas has been a Titan-like Miller-Urey experiment in which gases gen (N2), and poor in methane and ammo­ mix: 90 percent nitrogen and 10 percent such as methane (CH4), water vapor (H20) nia. In this sort of atmosphere, the chemi­ methane. The solid organic material pro­ and ammonia (NH3) were sparked with cal pathways leading to life would have duced in these simulations has properties simulated lightning, producing a variety of been very different from those explored very similar to the organic haze observed organic molecules-including many key by Stanley Miller and his colleagues. on Titan. biomolecules. Stanley Miller first per­ This new view of the early Earth sug­ Titan's upper atmosphere may be a nat­ formed these experiments in the early gests that the organic compounds neces­ ural Miller-Urey experiment. Although 1950s, while he was a graduate student at sary for life were not made on Earth but there may be copious organic production the University of Chicago with Harold C. were imported by comets and meteorites. on Titan, its great distance from the Sun Urey. Investigations of comets have shown them means that water cannot exist as a liquid at At the time Miller did his experiments it to be rich in organic molecules, and re­ the low temperatures on its surface. This was thought that Earth's early atmosphere searchers have even found amino acids lack of liquid water is a serious obstacle was rich in hydrogen (H2) and its com­ within meteorites. on the road to life and limits the analogy pounds, such as methane and ammonia, Scientists are still hotly disputing these between prebiological Earth llPd present­ but very poor in the oxygen so necessary two competing views of the evolution of day Titan. - CPM

In these oceans or lakes would also be the accumulation a key role. Even though it is present in only small amounts, of billions of years worth of complex organics produced in it absorbs radiation in parts of the spectrum that the more the atmosphere. The major product, ethane, would mix with abundant gases methane and nitrogen do not. the methane, making a clear liquid. Most of the other or­ ganic products would sink to the ocean floor or collect on Methane Rain the continents. There are some interesting similarities between the roles played by the greenhouse gases methane and hydrogen on Examining the Greenhouse Effect Titan and water vapor and carbon dioxide on Earth. As Titan's thick atmosphere produces a strong greenhouse ef­ you know from reading the newspapers, it is the rise in fect. The atmospheric greenhouse effect, long known on our carbon dioxide in Earth's atmosphere resulting from our own planet, was discovered on Venus in the early 1960s by industrialized life-style that has triggered the alarm about Carl Sagan, and it was subsequently found to affect other greenhouse warming. planets in the solar system. Hydrogen on Titan and carbon dioxide on Earth are In a horticultural greenhouse, from which the planetary present in lower concentrations and play smaller roles in greenhouse derives its name, the panes of glass allow solar the greenhouse effect than do methane and water vapor. energy to enter but prevent hot air or infrared heat energy On Earth, the atmosphere can only hold a limited amount (emitted by objects when heated) from leaving. The glass of water vapor; when the atmosphere becomes saturated, barrier keeps the heated air inside from mixing with cooler the water vapor condenses to a liquid and falls as rain. air outside. This one-way energy flow heats the greenhouse, The same may happen to methane on Titan. keeping the inside warmer than the outside. The amount of a gas like water vapor or methane that In a planetary atmosphere, the greenhouse effect operates an atmosphere can hold is determined by its temperature. on the same basic principle. The greenhouse gases on Earth, For example, on a hot summer's day Earth's atmosphere Venus and Mars-water vapor (HP) and carbon dioxide can hold much more water vapor than on a cold day, result­

(C02)-allow solar energy in ordinary visible light to reach ing in the high humidity that produces discomfort. the planet's surface, but they block some of the infrared By contrast, the concentrations of hydrogen on Titan heat energy radiated away by the surface. Titan's green­ and carbon dioxide on Earth are not limited by saturation, house gases-methane, nitrogen and hydrogen--do the so these gases will not rain out of an atmosphere. If their same thing. The atmospheric gases then radiate some of this concentrations were to change, then the temperature of the energy back to the surface, thereby warming it. surface would change. This temperature change would be The magnitude of this greenhouse warming compared to amplified by corresponding, and much larger, changes in the direct heat from the Sun is an indication of the strength the concentrations of methane on Titan and water vapor of the greenhouse effect. By this measure Titan has the sec­ on Earth. ond strongest greenhouse effect in the solar system-after Thus hydrogen on Titan, like carbon dioxide on Earth, Venus, of course. plays a key role in climate evolution. Understanding the 6 Of the main greenhouse gases on Titan, hydrogen plays processes that control its concentration is critical to develop- THE GREENHOUSE EFFECT A planet's surface is warmed byener­ l gy that it receives from the Sun, which shines brightest in light from the por­ tion of the electro­ magnetic spectrum visible to human eyes. The planet GREENHOUSE GASES cools by emitting infrared radiation, which we could sense as warmth. A greenhouse effect arises when certain gases block the es­ cape of the infrared radiation and radi­ ate it back to the surface. This raises the surface temper­ ature even more. Illustration: R. G. Smith

ing our understanding of the history of Titan's atmosphere. We also learned the reason for the cold temperatures in our simulations. If the pressure on Titan is reduced, the An Opposing Force greenhouse effect is diminished, since it is mostly due to The picture on Titan is even more complicated. In addition gases in the very lower parts of the atmosphere. The anti­ to a greenhouse effect, it has an antigreenhouse effect. This greenhouse haze, by contrast, is high in the atmosphere. effect was the key to explaining the surprisingly cold tem­ If the pressure gets low enough, the greenhouse effect be­ peratures we encountered in our computer simulations. The comes small and the antigreenhouse effect dominates. Then, 'upper atmospheric haze layer blocks incoming solar energy with only the antigreenhouse e!fect, Titan becomes cold. but allows the surface radiation to escape freely. Hence, we call this layer an anti greenhouse layer. Toward Understanding Earth The organic substances that compose the haze are dark Expending all this effort to understand the behavior of gases brown and orange and are very opaque to visible light, the surrounding a moon over a billion kilometers away may region of the electromagnetic spectrum in which our Sun seem like debating how many scientists can dance on the shines most brightly. But these same organic substances are head of a pin. But the behavior of similar gases on Earth virtually transparent to the infrared radiation that comes may have determined if life could arise here. And the in­ from the surface of Titan. It's like being in the shade with crease in greenhouse gases, triggered by one of the more no clothes on. You are cooled (by convection and radiation), highly evolved life-forms, may be changing the environment but you are not being warmed by the Sun. So, in opposition on our home world. In trying to understand greenhouse to the greenhouse effect, which warms a planet's surface, warming more fully, it helps to have examples from more the antigreenhouse effect cools a planet's surface. than one planet. As we found out, the study of other worlds Once we realized the difference between the greenhouse often holds surprises that can be lessons in how planets and antigreenhouse in Titan's atmosphere, we used our com­ work. puter simulations to investigate the relative roles of these The Voyager 1 flyby of Titan allowed us to explore first two effects. We began by modeling the simplest case for the greenhouse effect induced by atmospheric gases other Titan, as if it were a body with no atmosphere at all. In this than carbon dioxide and water vapor, and now the antigreen­ case, sunlight would warm its surface to minus 191 degrees house effect due to organic haze particles. We can carry our Celsius (minus 312 degrees Fahrenheit). This is called the research only so far with the data we have available to us. effective temperature. To deepen our understanding of Titan, a world tantalizingly Carrying our calculations further, we saw that the green­ similar to our own, we need to go back. house effect on today's Titan warms the surface above this NASA and the European Space Agency have plans for effective temperature by 21 degrees Celsius (38 degrees a mission to Titan that will send a probe through the atmo­ . Fahrenheit). But at the same time, the antigreenhouse effect sphere to the surface and a Saturn orbiter whose radar will cools the surface by 9 degrees Celsius (16 degrees Fahren­ "see" through the clouds of Titan. Known as the Cassini heit). orbiter and Huygens probe mission, this ambitious project The net result, since the greenhouse effect is the stronger should help us unlock more of the secrets of this strange of the two, is that the surface is currently 12 degrees Celsius world that may be able to tell us so much about our own. (22 degrees Fahrenheit) warmer than the effective tempera­ ture. If the antigreenhouse haze layer were somehow re­ Christopher P. McKay and James B. Pollack are planetary moved, then the surface temperature would be 23 degrees scientists at NASA Ames Research Center in California. Celsius (41 degrees Fahrenheit) warmer than the effective Regis Cow·tin is a planetary scientist at the Paris Observa­ temperature. tory in Meudon, France. 7 hy Edward Belhruno

have always been mesmerized by the Moon, that body that lights the I night sky and tantalizes us with its closeness. As a mathematician, I study ways to reach it. As an artist, I paint it. My fascination with Earth's beckoning satellite led me, in 1985, to the Jet Propulsion Laboratory (JPL). My field is celestial mechanics, which means that I apply equations de­ rived from Isaac Newton's law ofuni­ versal gravitation to the motions of ob­ jects as they travel through space. One of the milestones in this field was Ed­ mund Halley's prediction that the comet he saw in 1682 would return to Earth's vicinity in 1758. It showed up right on time, and posterity honored Halley by naming the comet after him. Another milestone was reached in the 1920s, when W. Hohmann discovered a Author Ed Belbruno is an artist as well as pathway to the Moon. During the 1960s a celestial mechanician. In this painting he and 1970s, the glory days of lunar ex­ theory to the Lunar Get-Away Special visualizes an Earth-Moon transfer orbit ploration, every spacecraft that traveled mission- a mission unfortunately des­ through a fuzzy boundary. Painting: Edward Be/bruno to the Moon, including the Apollo tined never to fly. (The Get-Away Spe­ spacecraft, followed Hohmann's classic, cials were small, self-contained experi­ three-day route. ments that could be easily carried in the But, in 1985, some new fmdings in cargo bay of the space shuttle.) Not un­ Hohmann transfer. celestial mechanics indicated that there til 1991 did someone fmd a way to ap­ The general idea is that a spacecraft just might be more efficient routes. My ply fuzzy boundaries to a spaceflight fires its rocket engines to leave a park­ curiosity piqued, I asked some aero­ project- in a most spectacular fashion. ing orbit about Earth. It then coasts for space engineers if a better way to travel Moreover, the spacecraft, Hiten, was about a quarter of a million miles to the from Earth to the Moon was a possibil­ flown not by NASA, but by the Japanese Moon. Next, it fires its engines again to ity. Every one of them gave me the Institute of Space and Astronautical slow down, just enough to permit the same answer: a resounding no. After Science (ISAS). It reached the Moon on Moon's gravity to capture it into orbit. all, I was told, the space programs of October 2, 1991, using a radically new If the spacecraft does not slow down, it both the United States and the Soviet route. James K. Miller of JPL and I will zoom past the Moon into inter­ Union had used this route for every one worked out the trajectory that Japan planetary space. of their missions. Certainly, someone followed to become the third nation in The Hohmann transfer is essentially in the generations of rocket scientists history to reach the Moon. an ellipse with Earth at one focus, as since the 1920s would have found a Figure 1 (page 10) shows. All space­ better way if it existed. Starting Point: The Classic Route craft trajectories are segments of hyper­ That sounded reasonable-but the How did this unlikely story come to bolas or ellipses, and the planets all fol­ quickness of their responses bothered pass? Many people and events had to low elliptical orbits about the Sun. me. I decided to see for myself. come together for this new approach to (Newton used Kepler's laws of plane­ space travel to be proved. Let's back tary motion, which describe these ellip­ Introducing Fuzzy Boundaries up a bit and see how the search for a tical orbits, to derive his law of univer­ After two years of work, I developed a better route to the Moon evolved. sal gravitation, but that is another story.) theory that enabled me to produce the The classic, three-day route to the This transfer requires some very re­ first proof showing that there is a sub­ Moon had been discovered by strictive assumptions. That is, when stantially better way to get to the Hohmann in his efforts to find a trajec­ calculating the transfer, a celestial me­ Moon. This theory introduced the no­ tory that minimized the energy needed; chanician allows the spacecraft to inter­ tion of "fuzzy boundaries." (I'll detail that is, one that would require the least act gravitationally with either Earth or this somewhat fuzzy concept later.) amount of fuel to reach the Moon and the Moon, but never with both at the 8 Mission designers at JPL applied the enter orbit. His solution is called the same time. This is called a two-body interaction-the two bodies being sion. Although this work enabled the the planetary object and the space­ LGAS study to progress, the concept craft. was not accepted by some of my col­ leagues at JPL. This was, of course, Moving Forward: disappointing. Ballistic Capture There were several obvious reasons When the spacecraft is allowed to in­ for the skepticism. Ballistic capture teract with both Earth and the Moon was a new concept in mission design, at the same time throughout its mo­ as were fuzzy boundaries. Further­ tion, the range of possible transfers more, the LGAS spacecraft would becomes more complex. These are have used an unconventional form of called three-body interactions, and propulsion, tapping electricity for they are so complex they are almost power. So I then set out to extend my impossible to calculate without the results to include the standard chemi­ help of a high-powered computer. cal rockets used in practice. Three-body interactions allow us I thought this would be easy, but I to work out a transfer in which the was wrong. A spacecraft using elec­ spacecraft is captured by the Moon tric propulsion moves in an entirely without using rocket engines, thus different way than does a spacecraft expending no precious fuel to ac­ powered by chemical rockets. With complish this maneuver. This is electric propulsion, ionized atoms­ called a ballistic capture, and it rep­ atoms having an electrical charge­ resents a substantial improvement shoot out the back of the spacecraft, Called Muses-A at its launch in over the Hohmann transfer to the giving it a very small push. So it can January 1990 Moon. Fuzzy boundaries are what take one to two years for such a craft chance to apply fuzzy boundaries to and later re­ allow ballistic capture to happen. to reach the Moon. This would leave chemical propulsion. named Hiten, this spacecraft So what are these fuzzy bound­ plenty of time to make careful adjust­ James K. Miller, an engineer at carried the small aries? The Moon's fuzzy boundary ments to reach the fuzzy boundary. JPL, walked into my office and told subsatellite can be thought of as a region sur­ However, a spacecraft using me that he was working on a prob­ Hagoromo to the rounding the Moon where a space­ chemical rockets can reach the Moon Moon, where the lem with a Japanese spacecraft smaller craft's craft, as it moves, feels the gravita­ in three days. It seemed from my called Muses-A. In January, it had transmitter tional effects of both Earth and the work that it would be impossible to been launched into Earth orbit carry­ failed. Hiten exe­ Moon nearly equally. As a spacecraft reach the lunar fuzzy boundary from ing a daughter spacecraft designed to cuted a series of lunar swing-bys travels in this region, it will not know Earth at these speeds. For three more fly on to the Moon. The second in 1990 and Earth whether to move toward Earth or the years I examined this problem. My spacecraft had not performed as aerobraking Moon. Its motion will appear chaot­ colleague Jaume Llibre, from the planned, and the first Japanese lunar demonstrations .in 1991. Then, ic. Only a slight nudge is needed to mathematics department at the Au­ mission seemed doomed to failure. following a path allow the spacecraft to be captured tonomous University of Barcelona, Then, someone had the idea that discovered by by the Moon's gravity. worked with me on this difficulty the mother ship, Muses-A, might be the author and James Miller, the A spacecraft can be captured by while researching another problem. able to complete the mission. But it spacecraft un­ the Moon without using rocket fuel We had no luck. would not be able to reach lunar orbit dertook a new if the celestial mechanician can find In January 1990, JPL lost confi­ using the standard Hohmann trans­ mission to orbit a transfer trajectory from Earth to the dence in my line of research, and I fer; slowing it down would take too the Moon. Photograph: Institute fuzzy boundary. The search must be pursued work elsewhere. By the end much fuel. Miller asked me if my of Space and Astro­ done on a computer. Although the of May, I had accepted a position at fuzzy boundary theory might be nautical Science .boundary is a complicated, higher­ Pomona College of the Claremont applicable. dimensional mathematical construct, Colleges as a Visiting Associate I looked at the ceiling and silently we can say the spacecraft is in the Professor of Mathematics. said, "Thank you." boundary if it is at a specified dis­ I explained to him that a way to tance from the Moon and moving at Bach on Course solve the problem would be to start the correct velocity. I tried to put the years of fuzzy at the desired endpoint-at the boundary work behind me. My mind Moon. Assume that the spacecraft A Temporary Setback was on the future. Then, on the day I was already at the fuzzy boundary in In 1987, I had demonstrated that the resigned myself to the idea that my a captured state. Then work the prob­ Lunar Get-Away Special could use work was not going to bear fruit, at lem back in time to fmd out where ballistic capture to conduct its mis- least in my lifetime, there came a the spacecraft had to be to get there. 9 Figure 1-This is the classic Hohmann trans­ ber2,1991 system. Such an array of widely fer trajectory from Earth to the Moon. At point A, (Figure 2). spaced instruments might be able to the spacecraft fires its Although detect gravity waves from the uni­ engines and leaves its Hiten could verse. Gravity waves are predicted by parking orbit about Earth. After traveling have fired its en­ Einstein's theory of relativity, but no three days, it fires its gines and gone one has yet detected one. engines again to slow into lunar cap­ With imagination and hard work, down so that the Moon's celestial mechanicians may fmd even gravity can capture it ture on October into lunar orbit. 2, the fuel saved more ways to use fuzzy boundaries to by taking this send spacecraft and scientific instru­ Figure 2-This is the al­ ments out to gather information and path to the Moon new route through the Earth-5un lowed the space­ teach us more about our universe. fuzzy boundary. The craft to travel In closing, I'd like to note that, in spacecraft leaves Earth beyond the 1988, Thomas R. McDonough, coor­ and flies by the Moon, where it picks up an Moon and per­ dinator of The Planetary Society's extra push from the form other ex­ program in the Search for Extraterres­ Moon's gravity. It then periments in the trial Intelligence, predicted the out­ travels to the fuzzy boundary, where it feels Earth-Moon come of our work on fuzzy bound­ the effects of the Sun's system. Hiten aries. In his book, Space: The Next 25 gravity and Earth's returned to the Years, he wrote, "Research is taking nearly equal/y. The spacecraft's trajectory Moon on Febru­ place that will profoundly reduce the then carries it back to­ ary 15, 1992, cost of getting into space. For exam­ ward the Moon. When it and was finally ple, mathematicians Edward Belbruno reaches its target, the lunar gravity captures inserted into and Jaume Llibre have made break­ the spacecraft into orbit lunar orbit. throughs in the calculation of orbits without the use of brak­ and trajectories that could greatly re­ ing engines. Extending duce the amount of fuel needed to get Illustrations: Michael Carroll the Concept to the other planets. This may bring After this the cost of interplanetary exploration demonstration, down to the level at which Japan and Then hope that this position is acces­ Miller and I showed that our methods other countries could compete with sible, with little modification, from would work for any spacecraft leav­ the superpowers." Muses-A's orbit about Earth. ing a parking orbit about Earth, in­ It looks as if McDonough had a cluding the now-defunct Lunar Ob­ crystal ball. Curio user and Curio user server mission, a casualty of cuts in Miller verified that itwas possible, the NASA budget. We found that our Edward Belbruno is a consulting or­ and he found the starting point for methods could save about 25 percent bital analyst with the Jet Propulsion ballistic capture at about 1.5 million of the fuel needed for a Hohmann Laboratory, and an artist with paint­ kilometers (930,000 miles) from transfer. ings on display in Los Angeles and Earth at a very special place: the Using this new transfer, we can Paris. Earth-Sun fuzzy boundary. Thus, to send scientific in- our surprise, the Sun played a crucial struments to the role on the way to the Moon, repre­ Moon using a senting a fourth-body interaction. small, inexpensive So, to get to the lunar fuzzy bound­ rocket; a Pegasus ary, the spacecraft had to start from a rocket dropped position well beyond the Moon. from a jet plane Miller was able to modify M uses-A' s can deliver a sig­ orbit about Earth to have it fly past nificant payload to the Moon and use the Moon's gravity lunar orbit, as Rex to slingshot out to the special position Ridenoure of JPL at the Earth- Sun boundary. and I have recently Thus we found a path to the Moon shown. for Muses-A, a trajectory that required Ronald Hellings no fuel for lunar capture. The total of JPL is studying flight time was estimated to be about another potential five months. application of the At the end of June 1990, after re­ fuzzy boundary fining and documenting our work, we transfer. This faxed a report off to ISAS. They veri­ could deliver the The Moon tantalizes us with its seemingly eternal, yet always changing face. In this photo, that familiar face appears ilIumi· fied our findings in three days. In late components of a nated by earthshine, or light reflected off Earth's surface. The Apri11991, Muses-A, renamed Hiten space-based inter­ bright arc of light is the region lit by sunshine, with its features after a Buddhist angel who plays mu­ ferometer to spe­ burned out in this exposure. sic in heaven, was diverted to this ciallocations in Photograph: Kerry Hurd, courtesy of Dennis Milon 10 route. It reached the Moon on Octo- the Earth-Moon 1eQing" 0 fIe 0 EartIt: Remote Sensing in Russia

blJ Rrnold 5. 5eliuanou

ussia began observing remote sensing methods in Earth with the launch of three complementary systems: Rits first meteorological Resource-F for photography, satellite, Meteor, in 1967. This two Resource-O' s designed to was designed primarily to ob­ observe land masses, and serve cloud cover, but geolo­ Ocean-O to monitor the oceans. gists and other scientists soon Resource has been operating realized that the images would. under the direction of the com­ be useful tools for investigating mercial space agency Glavkos­ the planet's surface, as well as mos. its mineral resources. The appearance of the Resoun:e-F American Landsat in 1972 Satellites of the Resource-F stimulated further remote sens­ system (F here stands for the ing activities by Russia, and Cyrillic letter that carries the the 1970s saw the launch of same sound in English and be­ such satellites as the Kosmos, gins the Russian word for pho­ Meteor-Priroda and Ocean se­ tography) provide photograph­ ries. Cosmonauts aboard the ic images of specific surface Salyut orbiting space station areas. A Resource-F satellite also systematically imaged carries film into orbit, takes Earth, as those aboard Mir do pictures and returns the ex­ today. The approach taken by posed film to Earth. Russian scientists and engi­ There is an obvious draw­ neers paralleled the United back to this system: It takes a States efforts, but they em­ long time to fill the customers' ployed somewhat different orders. Moreover, the film is technical means to watch sensitive to only a narrow range Earth from space. of wavelengths, and the data are Remote sensing consists recorded in analog form, not as primarily of the acquisition of digital data easily processed by images using radiation in visi­ computers. These limitations ble, infrared and radio wave­ are compensated by the unsur­ lengths (see box on page 14), passed quality of the images, but other observing systems with great surface detail. using various instruments are also possible. Resoun:e-O By 1980, Russia had devel­ The letter 0 is the first letter in oped a system called Resource the Russian word for fast-an that combined several different appropriate designation for a ABOVE: At the some time Resource-O took the image at right, the satel­ lite's higlHesolution camero, MSU-E, obtained this folse-color image. This is an enlarged view of the piece of land that now divides the Ami Sea into two separate reservoirs. The area shown is about 30 kilome­ ters (19 miles) wide, with details visible down to 45 meters (lSOJeet). RIGHT: The Aral Sea in Russia is rapidly drying out, triggering on ecologicol disaster for the region. (honges to this large lake can be monitored from space. This folse-color image was obtained by the moderate-resolution camero MSU-SK on the Resource-O satellite. The area covered is 600 kilometers (370 miles) wide, with details visible down to 170 meters (560 feet).

system of data transmission using ra­ dio and television. Resource-O is the second generation of a multispectral television system designed to observe Earth from space, following the pio­ neering Meteor-Priroda. Covering the enormous area of the former Soviet Union was a particular concern in the design of Resource-O. The country stretched across 11,000 kilometers (over 6,800 miles). Obser­ vations over several days were needed to monitor the hydrological situation, to study the vegetation, to look for for­ est fires and to investigate the distribu- .------.With its moderate-resolution scanner, the satellite Resource-O l is able to record data for broad swaths of Earth's surface_ This image, covering an area 600 kilometers (370 miles) wide, shows regions of Kazakhstan, northern China and the lien Shan Mountains. .

ters (400 miles). This camera can see an area 600 kilometers (370 miles) across with details visible down to 170 meters (560 feet). The camera sees four chan­ nels in the visible and near-infrared part of the spectrum, with a special channel that can measure surface temperature. The data from Resource-O satellites are recorded on board and then delivered to receiving stations in Moscow, Novosi­ birsk and Khabarovsk. MSU-SK can observe any area on Earth. The two center images on these pages are exam­ ples of its work. However, there are certain problems that MSU-SK cannot solve alone. The satellite also carries two high-resolution MSU-E cameras with overlapping fields of view. Each covers a ground swath 45 kilometers (28 miles) wide, so the two cameras together cover about 80 kilometers (50 miles). They can see details down to 45 meters (150 feet) in three spectral channels, two in the visi­ ble and one in the near-infrared. The cameras use charge-coupled devices as detectors, and we have the ability to point these cameras with commands from the ground. They act as magnify­ ing glasses within the field of view of MSU-SK. The Resource-O combination of a survey camera with high-resolution, tion of various types of pollution. the optical spectrum while scanning pointable cameras is one of the differ­ For these purposes, a multispectral across the satellite's ground track. ences between Resource-O and the television system with moderate sur­ With this capability, we have obtained American Landsat and the French face resolution (it can pick out details panoramic surface images in false color SPOT. This combination is very advan­ from 100 to 250 meters across) proved that are several thousand kilometers tageous. The inset on the preceding to be the best solution. Such systems long. page is an image of a piece of land provide data swaths 600 to 1,200 kilo­ The best unit of this type is MSU­ that now divides the drying Aral Sea meters wide. They use multichannel SK, which is mounted on Resource-O (larger image) into two sections. radiometers that cover a wide range of and orbits at an altitude of 650 kilome- MSU-E obtained this image simul- through clouds, so surface features that would be hidden to llfhat Is Remote Sensing? human eyes are visible to the spacecraft. Thus, by captur­ ing the reflected microwaves, Magellan can see through ff Remote sensing" is a piece of engineering jargon the clouds that envelop Venus, and Ocean-O can track ice that recurs frequently in accounts of spacecraft even through a thick cloud cover. studies of the planets, including our own Earth. Another useful part of the electromagnetic spectrum The phrase gives the process of investigation a distant is the infrared, which ranges in wavelength from about sound, as if it were some arcane technique practiced only 1/30,000 to 1/100 of an inch (1 to 300 microns). Every­ by the scientifically initiated. But, actually, remote sensing thing in the universe at a temperature above absolute zero is something nearly everyone does every day. (minus 273.15 degrees Celsius or minus 459.67 degrees The act of seeing is a type of remote sensing. Eyes do Fahrenheit, the lowest temperature possible in any natural not make actual physical contact with the objects they system) emits infrared radiation. Our bodies detect such perceive. Instead, they collect information from a distance radiation as heat. But the heat sensors in our skin are lim­ -remotely-as light bounces off an object and is reflect­ ited in the amount of information they can convey. (If you ed into them. touch the fire, you will be burned; if you stay out in the Human eyes are sensitive to a narrow section of the snow, you will freeze.) electromagnetic spectrum, which extends from radio We can equip our spacecraft with sensors sensitive to waves thousands of kilometers long to gamma rays small­ infrared radiation that will tell us quite a bit about the ob­ er than individual atoms. The visible portion of the spec­ jects they study. For example, the Voyagers carried an in­ trum consists of waves ranging from about 16 to 32 mil­ frared system that determined the surface temperatures of lionths of an inch long (0.4 to 0.8 micron). But the the outer planets' moons as well as identifying some of the universe shines across the entire spectrum, and we can elements in the gaseous planets' atmospheres. construct instruments-artificial senses- to see in the Earth-orbiting satellites carry infrared detectors that can many different types of light. map the distribution of minerals, track algae blooms in the The wayan object absorbs, radiates, reflects or trans­ oceans and monitor the health of crops. As Professor Seli­ mits electromagnetic radiation betrays much about its na­ vanov describes, the Resource-O satellites, equipped with ture. By building remote sensing instruments sensitive to instruments sensitive to infrared, are closely watching the particular portions of the spectrum, we can determine decline of the Aral Sea, which is being decimated by pol­ composition, texture, temperature, altitude and many other lution and the loss of water to irrigation. types of information. Of course, since human beings are so closely attuned to Since space is an environment hostile to human beings, the sense of sight, we give our spacecraft remote sensors we have sent robotic surrogates to investigate the planets sensitive to wavelengths in the visible spectrum-the for us. We equip them with remote sensing devices, which robotic equivalents of our eyes. We create images that collect data and relay them back to us using radio waves show us what distant planets would look like if we could (a very useful part of the spectrum). see them in person. We also take the data gathered in in­ For example, the Magellan spacecraft is equipped with visible wavelengths and convert them into pictures so that radar to map the surface of Venus, seeing in a portion of our highly evolved eyelbrain combination can more easily the electromagnetic spectrum very similar to the one used appreciate their significance. by the Ocean-O system described on these pages. These So, remote sensing is not such an arcane thing after all. spacecraft, orbiting high above their respective planets, di­ It is a tool used in everyday life and in one of the most rect microwaves (high-frequency radio waves) at the plan­ fantastic adventures yet dreamed of by humanity, the et surface. It is the nature of microwaves that they pass exploration of the planets. -Charlene M. Anderson

taneously with the image of the larger they playa secondary role in the in studying regions with bad climates, region taken with MSU-SK. This area surveillance of the oceans. For this pur­ and in observing during the long polar is suffering an ecological disaster and pose, the microwave region of the nights. is under constant surveillance by the spectrum is preferable. We use both ac­ Russia actually began to study the Resource system. tive techniques- radars-and passive oceans from orbit in 1968 with the ones-radiometers. In microwave launch of Kosmos-243, which was O[ean-O "light," clouds are transparent and the equipped with radiometers working at Optical images from satellites are im­ instruments can "see" in either day or radio frequencies. Other satellites in portant in the study of land masses, but night. These are important advantages the Kosmos series followed, as did the ~ I satellite Ocean-E, allowing us to de­ l velop a variety of observing tech­ niques. The short-lived US Seasat, launched in 1978, and the Russian Almaz satellite, which launched at about the same time and operated un­ til 1987, scanned oceans using radars with resolutions of tens of meters per pixel. (A pixel, or picture element, is one dot in an image.) The Ocean-O satellites are based on a different concept, driven by a particular need of Russia: the system­ atic survey of polar ice in the Arctic and, occasionally, in the Antarctic to support expeditions to the area. Russia has a long coastline along a northern sea route. Lately, thanks to nuclear­ powered icebreakers and the continu­ ous stream of information about the polar ice provided by satellites, it has been possible to keep this route open for the entire year. The Kosmos-1500 satellite was the first in the Ocean-O series. It carried a radar that covered 460 kilometers (285 miles) with a resolution of2 kilometers (about 1.2 miles). Ocean-O enables us to produce, in just three days, a small­ scale map we can use to evaluate the ice situation. Although guiding the ships through the ice requires other El:olo!}il:al Surueillanl:e ment obtained the first high-resolution means of reconnaissance, such as air­ As readers of The Planetary Report thermal images of Mars. planes and helicopters, there have know, there is a strong connection be­ That recent planetary investigation been cases in which ice-trapped ships tween programs for observing Earth brought together many Russian and were rescued solely through the use of from space and the study of other American scientists and engineers in data from Ocean-O. planets, and not solely because Earth the new climate of perestroika. Be­ The radar images from this satellite is one of many planets in the solar fore that, we were competitors. Now are transmitted along with a video sig­ system. There is also a methodologi­ we have the opportunity to cooperate nal taken simultaneously by a high­ cal connection: Remote sensing is in the scientific study of Earth and the resolution sensor, MSU-M, operating still the primary means of gathering other planets in our solar system. in the visible spectrum. A partial information for planetary scientists In my opinion, this spirit of cooper­ MSU-M image 895 kilometers (550 to analyze. ation will result in the ultimate inte­ miles) wide is transmitted in the same This connection also holds for the gration of these satellite systems and frame as the radar image. An example principles of instrument design. For other remote sensing systems into an . is seen at upper right. It illustrates the example, the optical- mechanical sys­ international system of ecological efficiency of radar observations of the tem described in this article is a direct surveillance. To some extent, that ap­ northern regions. descendant of the cameras that pro­ proach will be realized in the US Mis­ A great advantage of Ocean-O is its duced the first panoramic images of sion to Planet Earth. However, that ability to "dump" data to many small the Moon: Luna 9 in 1966 and Luna program deals mainly with the integra­ stations that receive transmissions 19 in 1971. tion of information. Some program from mefeorological satellites. Most Conversely, many parts of the should be created that is oriented more of its information is also received by MSU-SK scanner on Resource-O toward the study of ecological prob­ the same ground-based means as the were used in the Thermoscan instru­ lems. Our suggestions on this matter Resource-O system. ment carried on Phobos 2. This instru- have been forwarded to NASA. 0 shop the Society held in 1987 The Rover Expo is free space are permitted to jom. ", . and the one conducted in and open to the public. It Hundreds of astronauts and Bangalore, India, last year. will coincide with the World cosmonauts from around the In February, Executive Direc­ -LDF Space Congress, also being world will gather at the asso­ tor Louis Friedman spoke at held in Washington, DC. ciation's annual convention the United Nations' special -Susan Lendroth, Manager in Washington during the last International Space Year ses­ An updated index for The of Events and Communica­ week of August. The theme sion of the Committee on the Planetary Report is now tions of this year's convention is Peaceful Uses of Outer Space available. For a copy, send "To Mars, Together." (COPUOS). Substituting for $3.00 to TPR Index, c/o the The public event will be Society President Carl Sagan, Society. -Mitchell Bird, the final session of ASE' s who was felled by the flu, Dr. Production Editor Congratulations to the win­ convention, and it will honor Friedman addressed interna­ ners of the H. Dudley Wright the 20 winners in the Soci­ tional delegates, leaders of International Student Con­ ety's H. Dudley Wright Inter­ space agencies, and a full gal­ test, "Together to Mars." national Student "Together to lery on the subject of space­ On September 1 and 2, the To enter the competition, Mars" Contest. flight and global unification. International Space Year Ex­ students had to write about a For information on tickets, In addition to describing hibition of Robots and Tele­ specific aspect of a human write to ASE Event, c/o the results and opportunities in presence for Exploring New mission to Mars. About 900 Society. -SL planetary exploration, Dr. Worlds, or "Rover Expo," entries were received from Friedman spoke of the inter­ will be held adjacent to the more than 30 countries, rep­ national educational pro­ Smithsonian National Air resenting every populated grams in which the Society is and Space Museum in Wash­ continent on Earth. Topics International Space Year, involved. The H. Dudley ington, DC. ranged from life-support sys­ 1992, is under way. The Plan­ Wright International Student In addition to The Plane­ tems for Mars missions to de­ etary Society, the National Contest, Latin American edu­ tary Society and the Smithso­ tailed analyses of materials Space Society and Final Fron­ cational workshops and inter­ nian National Air and Space needed to withstand the radi­ tier: The Magazine of Space national team participation in Museum, the following orga­ ation of interplanetary space. Exploration have joined to­ the Mars Balloon and Rover nizations are cosponsors of Winning entries were gether to publish a free direc­ projects were cited. the Rover Expo: the NASA from the following countries: tory of special events. The di­ The participation at the Offices of Exploration, of Argentina, Colombia, France, rectory is available to all our COPUOS meeting was the Aeronautics and Space Tech­ Germany, Great Britain, members. Write for your first by The Planetary Soci­ nology, and Space Science Hungary, India, Ireland, Is­ copy of the ISY Directory c/o ety since receiving its non­ and Applications; the Space rael, the Netherlands, Poland, the Society. -SL governmental organization Automation and Robotics Portugal, Spain, Ukraine and (NGO) special consultative Technical Committee of the the United States. status with the UN Econom­ American Institute of Aero­ -Barbara Bruning-LaBelle, ic and Social Council. nautics and Astronautics; the Program Coordinator, H. -Louis D. Friedman, Execu­ French space agency, Centre Dudley Wright International tive Director National d'Etudes Spatiales; Student Contest and the Russian Mobile Vehi­ cle Engineering Institute. Working demonstrations of

Two space science educators' rovers from government and The Planetary Society will II conferences are planned for private industry will be given join forces with the Associa­ II November 1992, under co­ in open-air enclosures. All tion of Space Explorers . ~ .~ sponsorship of the UN, the the rovers will feature abili­ (ASE) to host an exciting European Space Agency and ties applicable to planetary public event in Washington, The Planetary Society. The exploration, such as naviga­ DC, on August 28. first conference is in Costa tion, grasping and remote ASE is an organization Rica, the second in Colom­ sensing. When not in use, the with an unusual requirement bia. These build on the suc­ rovers will be on display for membership-only indi­ 16 cessful Mexico City work- near the demonstration area. viduals who have flown in by Louis D. Friedman

WASHINGTON, DC- Responding • the needfor small missions, such as He replied: "France is strongly sup­ to the threat to planetary exploration the proposed Space Exploration Initia­ portive of these multinational Mars contained in the administration's fiscal tive lunar precursor, to supplement, missions and is very willing to see year 1993 budget, as detailed in the but not to displace, mid-sized plane­ them succeed. We believe, at CNES, March/April 1992 issue of The Plane­ tary missions. in such cooperative projects, which tary Report, The Planetary Society ur­ There is still a need for mid-sized are essential to make active use of the gently requested that Congress hold planetary missions, such as Mariner, unique opportunities afforded by hearings on the issue. Pioneer, Voyager, Magellan, and Mars space to conduct research in fields The Senate Subcommittee on Sci­ Observer. In our testimony, we focused such as planetary exploration. I can ence, Technology and Space, chaired on the Cassini mission now under de­ assure you that CNES, for its part, by Sen. Albert Gore, Jr., and the House velopment, since after the cancellation will continue its best efforts to help Subcommittee on VA, HUD and Inde­ of its sister mission, the Comet Ren­ such programs." pendent Agencies, chaired by Rep. Bob dezvous Asteroid Flyby, this mission Traxler, agreed to hold hearings. Soci­ is seriously threatened. WASHINGTON, DC-Sen. Barbara ety Vice President Bruce Murray testi­ Cassini would orbit Saturn to study Mikulski, Chairman of the Senate Sub­ fied before the Senate, and Executive the planet, its rings and moons. The committee on V A, HUD and Indepen­ Director Louis Friedman testified be­ spacecraft would carry a probe, called dent Agencies, held hearings on how fore the House of Representatives. Huygens and built by the European the US could use the capabilities of the In constructing our testimony, we Space Agency (ESA), that would in­ Russian space program. She then had to balance the issues carefully. vestigate the atmosphere of Titan. wrote President Bush and Secretary of With the economic problems facing As originally planned, Cassini was State Baker asking them to take action Congress, it would have been neither an expensive mission, with an estimat­ on the issue. right nor effective simply to argue for ed cost of over $1.6 billion. A reduc­ Rep. Ralph Hall of the House Sci­ more money for NASA. Indeed, to tion in cost is justified, and without it ence, Space and Technology Commit­ meet other budget constraints, it is the project will never survive the bud­ tee also held hearings on the topic. likely that Congress will have to make get process. We supported the cuts but Former President Reagan submitted additional cuts in the space agency strongly stated the need to preserve the some remarkable written testimony. budget. basic mission plan, with a launch in He suggested that the US could save This is an excerpt from our opening 1997. taxpayers' money by working with the statement: Weare asking all Planetary Society Russians in space. NASA was born in 1958, a positive members in the United States to write In his testimony, Reagan asked: side effect of the deadly serious Cold their senators and representatives in "Are there ways America can save War. Now, three decades later, the support of the Cassini mission. The time and money building [space sta­ Cold War is over. Suddenly, the cancellation of this mission would end tion] Freedom by using CIS [Com­ geopolitical and economic situation in the development of planetary missions monwealth of Independent States] the world is vastly different. in both NASA and the European Space equipment and experience? Could we To meet the challenges of this new Agency. one day travel with the Russians to the world, NASA must refocus its energy If you would like the full text of our planet Mars, as some have suggested? and find a new raison d' etre. Its plane­ statement, please write to: Congres­ That wasn't my kind of thinking 10 tary program is no exception. Our fleet sional Statement, The Planetary Soci­ years ago, but ironically, it may not be of exploratory spacecraft needs to be ety, 65 North Catalina A venue, worth thinking about 10 years from reevaluated and revamped. We argue Pasadena, CA 91106. now if the CIS space program shuts in favor of such changes, but we also down for lack of funds." caution not to let these changes be­ P ARIS- The French space agency, The Defense Department is buying come an excuse to scuttle the fleet it­ the Centre National d'Etudes Spatiales some space technology components self. Specifically, we call to the atten­ (CNES), has set up a hard currency re­ from Russia, including the Topaz nu­ tion of Congress: serve fund to help ensure the survival clear reactor. This appears to be a new • the importance of maintaining the of the Russian Mars '94/'96 project. direction for the White House, and in­ American/European Cassini mission, (See the March/April 1992 Planetary dicates a loosening of the restrictions even as it is scaled down; Report.) Because of The Planetary So­ on trade. Whether this will apply to • the shortsightedness of ending op­ ciety'S special nongovernmental role NASA is unknown. erations for Magellan while it is still on the project, we sent a letter of ap­ sending important new data from preciation to CNES' Director General, Louis D. Friedman is the Executive Venus; J.D. Levi. Director of The Planetary Society. 17 atmospheric transport of Triton's gases, and calculations concerning its reservoirs of ices, are what have continued to perplex researchers. Triton's geology would seem to re­ quire the presence of water ice, but none has been found. News Telescopic measurements over the last dozen years have revealed enormous global color changes on Triton, which some scientists attribute to "the snowfall of '83"; others demur. Reviews The plumes provide clues about what's going on. Several active plumes were seen in stereo, and there are pictures of other atmospheric features that blend into a prominent haze layer. In addition, there is a whole family of dark surface features that bear an uncanny resemblance to the dark wind by Clark R. Chapman streaks on Mars. Imagine: wind streaks being deposited on the surface of a body with an atmospheric pressure just a few millionths of the sea level pressure on Earth! But there they are. Their directions hint at the wind flow, but differ from the orientations of the active plumes. Maps of where ince William Lassell' s mid-19th-century discovery they are and where they're not across Triton's surface of Triton, the giant neptunian moon has been the should tell us more about what is going on. Unfortunately, S subject of much speculation but little concrete Voyager's fleeting portraits of Triton don't show all parts knowledge. Then, on August 25, 1989, human technology of that world to equal advantage, so it is difficult to be brought us 100,000 times closer to this mysterious world. sure we've mapped all the streaks. And we won't get an­ Triton was the star of the show during Voyager's final plan­ other spacecraft back to Triton to double-check for a long, etary encounter. Scientists have been poring over the data long time. ever since. An issue of Science magazine published in October 1990 Origins discussed implications of Voyager's Triton pictures, partic­ One of the most intriguing things about Triton concerns its ularly the wholly unexpected geyser-like plumes. But there origins. The idea that it is a Pluto-like body that somehow was little consensus, with explanations ranging from dust got captured into orbit around Neptune early in that plan­ devils to something called a solid-state greenhouse, in et's history was gaining favor long before Voyager's flyby. which sunlight is trapped in an extensive, porous, translu­ Dynamical capture of a body orbiting the Sun into a moon­ cent surface layer of nitrogen ice. like orbit around a planet is a physicist's nightmare of a By January 1992, when a scientific conference on Nep­ problem, but proto-Triton could have been unlucky. It may tune and Triton was held in Tucson, Arizona, ideas about simply have crashed into a neptunian moon and been cap­ Triton's geysers continued to mUltiply. But other aspects of tured that way. Triton's unusual nature proved even more fascinating and Once in orbit around Neptune, in an initially very elon­ controversial. Just one example: Why is Triton's sunlit pole gated orbit, Triton may have "cleaned out" many preexist­ so icy? A book about Neptune and Triton is being written ing neptunian satellites, which would explain Neptune's by the scientists who attended the meeting. Since it is lack of a regular satellite system like those of other outer hoped that this latest project in the University of Arizona planets. Although Triton is big enough and rocky enough to Space Science Series will stand the test of time, the scien­ have melted spontaneously early in its history, it would tist-authors are trying to reach some definitive conclusions have been heated even more by great tides. Such tidal heat­ in the wake of the debates at the January meeting. ing could have equaled that responsible for the sulfur vol­ As often happens, Voyager's approach toward Neptune canoes on Jupiter's moon Io, and raised Triton's surface in the 1980s spurred ground-based astronomers' interest in temperature to a comparatively balmy 150 degrees Kelvin Triton: It seemed like a fantasy world, whirling around its -more than 100 degrees Kelvin warmer than its current parent planet in a backward direction and covered-so it frigid state. The resulting early chemical, physical and geo­ was thought~with oceans of liquid nitrogen. There was logical evolution of Triton could well have been remark­ particular interest in Triton's seasons, with Voyager's en­ able. It remains to be seen if Triton has yielded enough counter nearly coinciding with the warmest south-polar clues to Voyager to shed further light on that history. temperatures on Triton in centuries. It had been predicted Regardless of Triton's history, however, it is a stunning that all of its south-polar ices would have sublimated and surprise that this world in the deep freeze of the outer solar been transferred to the colder northern hemisphere. But system should sport currently active geysers and sudden Voyager's cameras found Triton to be a glearningly bright changes in global color, and continue to mystify us with its world, with a large and especially bright south-polar cap, seasonal behavior. It makes us yearn for a closer look at its while its northern hemisphere appears darker and frost-free. possible twin, the planet Pluto. Though NASA has the Could Triton have dark frost? rocket power to launch a fast-track stunt flight to Pluto, it will remain for another generation to reconnoiter Pluto with Ices and Gases a full complement of instruments, or return for in-depth, In the first hours after Voyager's encounter, all attention follow-up studies of Triton. was riveted on Triton's weird geology. Its would-be oceans turned out to be frozen solid, and its atmosphere was mea­ Clark R. Chapman served on the 1991 NASA 1nternational 18 sured to be so thin that it is practically a vacuum. Yet the Near-Earth-Object Detection Workshop. NEWS BRIEFS 'l ) (continued from page 3) (continued from page 3) Nations purchase the hardware or operating rights on behalf of member nations, [provid­ these altitudes, go thousands of ing] urgently needed economic support. This could be a truly international opportunity. miles without refueling or stay high -THOMAS S.w. LANGFORD, Phoenix, Arizona in the sky for days, or weeks, at a time. All the designs resemble Thank you for awarding me the College Fellowship. As I've continued my college futuristic gliders that are pushed education, I have become more excited about pursuing a career in a planetary science­ through the scant upper air by giant related field. The current outlook for engineering has become somewhat pessimistic due propellers. to defense cutbacks and the recession. However, we are at a great crossroads. -from Warren E. Leary in The In the past, a great deal of our technological efforts have gone for either preparing for New York Times war or trying to defend against the possibility of war. In fact, some of the greatest devel­ opments have come as a direct result of these times of crisis. Due to the collapse of the Soviet threat, it is no longer a national security requirement to spend so much on improving our technology. However, in order to remain a leader, the United States needs to continue Ideally, the next NASA adminis­ to develop new technology by refocusing those energies previously focused on defense. trator will finish the shake-up of As The Planetary Society has promoted since its beginning, exploration of the solar the bureaucracy begun by Mr. system is where our focus needs to be. No longer do we need to concern ourselves with Bush. In the utopian NASA, prob­ the destruction of peoples on Earth, but instead, we need to aim for new horizons. I hope lems will be confronted directly, that the United States as a country realizes that we need to make a real commitment to and never glossed over. A new planetary exploration. In my future career, I plan to do everything that I can to make this standard of accountability will idea come to fruition. If there is anything that I can do to help The Planetary Society further enable outsiders to distinguish these goals, please let me know. between those who succeeded on -PAUL KILLPACK, Provo, Utah a NASA project and those whose management mistakes produced a Educators are concerned that many of the students in the United States are not interested failure. New ideas will not be in the sciences, and they wonder what the future will be like if this lack of interest persists. frozen out by an entrenched team To help counteract this, even in a small way, may I suggest the following to members: of big aerospace contractors and When a new issue of The Planetary Report arrives, donate the previous issue to your local lifelong civil servants. NASA mis­ high school science department. I'm sure that the teachers and students will find it inter­ sions will be dissected by experts esting and challenging. Who knows? Perhaps one student will become more interested in not because of the embarrassing space and the space program. political and technical mistakes Even though The Planetary Society is encouraging work in SET!, the Mars program they embody, but because they and other ventures, not that many people know about this work. Here's a chance to spread represent the finest work the coun­ the word. try can do. NASA will give the -ANN ZAWISTOWSKI, Walpole, Massachusetts American public something to cheer for, not something to shake I found the News Brief in the January/February issue on NASA's long-term study of the their heads over and wonder, what establishment of a lunar outpost and other sites for astronomical telescopes to be quite are we doing up there? exciting. I've always felt that the primary objective of any space program should be to -from Space News obtain knowledge. An observatory on the Moon would increase our knowledge of the universe a hundredfold. Perhaps it is time to cut our losses with the space station and redirect some of the sav­ ings to more robotic planetary missions. The data we would obtain far outweigh the At a time when many question heavy expenditures of a space laboratory. America's ability to do .quality Hopefully, with Daniel Goldin appointed as NASA's new administrator, the United work and make competitive prod­ States' space priorities will follow a more exploratory and scientific course. ucts, the spacecraft Pioneer 10 has -PETER SQUARINI, Lauderhill, Florida just completed two decades of sol­ id exploration of the solar system. Recent issues of The Planetary Report have reported on a series of serious budget set­ Scientists involved in a long and backs for planetary exploration. Retreating from such exploration would be a disaster for complicated argument over "big the United States space program, but I worry about senior officers of The Planetary Society science" versus "small science" responding to this deplorable situation by targeting space station Freedom as the cause of have observed that Pioneer 1D's the current crisis in planetary science. relatively simple, straightforward The real cause of the Comet Rendezvous Asteroid Flyby's cancellation and Magellan'S design is a key to its success. death warrant is the constrained budget situation facing NASA as a whole. The space sta­ The whole Pioneer family, de­ tion is costly compared to planetary missions, but if it were canceled outright most of its signed in the 1960s, is doing well: $2 billion would be diverted out of NASA to social programs or to reducing the national Pioneer 6, sent to orbit the Sun in debt. Some funds might go toward space science, but how long would that keep programs 1965, is the world's oldest working on track in an era of flat budgets? space probe. Pioneers 7 and 8 When budgets were increasing a few years ago, a lack of consensus in the space com­ are still completing solar studies. munity was merely an annoyance. Now it is a serious threat to the United States' future Pioneer 12 is circling Venus, and as a spacefaring nation. Is it too late for everyone to work together to build public support Pioneer 11 is leaving the solar for continued growth in the overall NASA budget? system after looping past Saturn. -:-JON R. WELTE, Chicago, Illinois -from the Baltimore Sun 19 Questions Answers ~ I

Could asteroids or comets be used as Kopff. Once having expended the fuel to would be to process the surface materi­ mock spacecraft to carry instruments achieve a rendezvous, there is little ad­ al to manufacture fuel for the space­ throughout the solar system and, some­ vantage to landing except for the study craft, but this is beyond current space day, the universe? of the comet or asteroid itself. technology. -Bill Merkes, Freeland, Washington It is generally easier to control a -DA YID MORRISON, NASA Ames spacecraft that is flying freely; for Research Center To use a comet or asteroid as a base for example, the communications antenna exploration, we would have to launch of a free-flyer can be kept constantly If one of the planets blew up, or was and navigate our spacecraft and instru­ pointed at Earth, while on the surface of destroyed by something, would a new ment package to exactly match its orbit, a rotating comet or asteroid Earth would planet take its place to keep a basic bal­ just as the recently canceled Comet be below the horizon half the time. ance to the solar system? Rendezvous Asteroid Flyby mission was About the only possible advantage of - Tricia Kempton, age 11, Prescott, designed to rendezvous with comet riding along on a comet or asteroid Arizona

The trail of a comet appears as a diagonal white streak across this infrared image of the sky. Comet trails were first recorded by the Infrared Astro­ nomical Satellite (IRAS) in 1983, but they were not ob­ served and character­ ized until 1986 when Mark Sykes found them in the IRAS data. Comet trails are narrow, continuous streams of large de­ bris particles (millime­ ters to centimeters in size) shed by comet­ ary nuclei as they travel about the Sun. The debris particles travel at about the same speed as their parent bodies. They trace out a portion of the comet's orbital path, sometimes for tens of millions of kilometers. Sykes and Walker suggest that trails are probably common to all short­ period comets. Image: Mark V. Sykes f', FACTINOS If a planet were destroyed, for ex- to be detected. If we don't fmd any, ample by a large impact, its material we'll have to use more sensitive would continue to orbit the Sun and equipment to look for stray radio Comets are actually frozen mudballs rather than much of it would accumulate again and infrared emissions. dirty snowballs, say Mark V. Sykes of the Universi­ into a new body, This may have -THOMAS R. McDONOUGH, ty of Arizona in Tucson and Russell G. Walker of happened during the formation of the Planetary Society SET! Coordinator Jamieson Science and Engineering, Inc., in Scotts solar system when millions of bod­ Valley, California. The two scientists have spent ies were present in a cloud of gas In answering Gerry Bogacz's years studying cometary dust trails (see photo on and dust around the Sun. question about the orbits of previous page) and have published their findings in Why don't the asteroids accumu­ Uranus' moons (see Q&A in the a recent issue of Icarus. late into a small planet between January/February 1991 Planetary Comet trails (not to be confused with comet tails) Mars and Jupiter? The answer is Report), William McKinnon casts are the principal means by which comets lose mass. that the gravity of giant Jupiter con­ some doubt as to whether or not These trails indicate that comets are 75 percent dust tinually perturbs their orbits, keep­ there is a "conventional align­ or dirt. This would make their nuclei far dustier and ing them stirred up and colliding. ment" for planetary spins because less icy than previously believed, they say. -JAMES D. BURKE, Technical "three out of nine planets are ret­ The mudball model is consistent with the idea that Editor rograde rotators." comets formed in the Uranus-Neptune region of the Which three planets are retro­ outer solar system rather than in icy molecular What if an alien culture does not grade rotators? clouds far out in space. As they shift into the inner want us to know about its exis­ -Nathan W. Cook, Sandwich, solar system, comets may evolve faster than previ­ tence and is blocking our attempts Illinois ously believed, becoming inactive, asteroid-like to find it? bodies, says Sykes. - Greg Myklegard, Ocala, The first and most famous case is -from Lori Stiles at the University of Arizona Florida Uranus, whose equator is nearly perpendicular to its orbit plane. The In the Search for Extraterrestrial In­ angle between the equator and the The European Space Agency's Ulysses spacecraft telligence (SET!), this is sometimes orbit plane is called obliquity, and in has found marked differences in Jupiter's magnetic called the Zoo or Quarantine Hy­ Uranus' case is listed at 98 degrees field from what the last Voyager spacecraft uncov­ pothesis. Some scientists and sci­ (with any angle over 90 degrees in­ ered there 12 years ago. In mid-February, Ulysses ence fiction writers have speculated dicating retrograde rotation). scientists reported that Jupiter's magnetosphere that an advanced civilization would The second case is Venus, whose pulsates in and out and is now almost twice as ex­ not want to contaminate a primitive equator is nearly in its orbit plane, tensive as it was when the Voyagers surveyed the one like ours with its culture. but which spins "backward" very region in 1979 and 1980. slowly. The obliquity is listed as This is inspired by those who ad­ Scientific instruments on the probe also observed vocate protecting isolated peoples 177 degrees, or only 3 degrees off less debris in the surrounding area, suggesting that the "vertical" perpendicular to the in tropical rain forests from contact volcanic eruptions on Jupiter's moon 10 have slowed orbit. With a day that lasts 243 with modern civilization, on the down since the Voyagers' visit. Earth-days, Venus is hardly spin­ grounds that they may lose their -from John Noble Wilford in The New York Times cultural heritage. Perhaps there are ning at all. The spins of Uranus and galactic preservationists who want Venus may have been altered by gi­ to keep our unique culture from be­ ant impacts, and it may be apt to ing disrupted by contact with the picture Venus' spin as having been A team of planetary scientists has concluded that alien equivalent of hamburger nearly stopped in its tracks. water contained in several meteorites found on Earth stands, fax machines and TV com­ The third case is Pluto. Its obliq­ came from Mars, bolstering theories that free-flow­ mercials. uity is listed as 122 degrees, indicat­ ing water once existed on the now-parched planet. If so, they may not be successful. ing, as for Uranus, that its equator is Everett Gibson of NASA's Johnson Space Cen­ Any advanced technological civi­ at a steep angle to its orbit plane. ter (JSC) in Houston and Haraldur Karlsson of lization is likely to give itself away The equatorial plane is also the Texas Tech University in Lubbock extracted tiny by stray electromagnetic emissions plane of the satellite Charon's orbit water droplets less than lI64 of an inch in diameter such as the radio, TV and radar sig­ around Pluto. In the case of Pluto, from six meteorites using a small vacuum chamber nals that we inadvertently broadcast - we have a twin mini-planet, whose atJSe. to the universe. And if they have axial tilt and rotation have probably The samples were then analyzed by Robert Clay­ huge structures in space, then these been influenced by tidal interactions ton and Toshiko Mayeda of the University of Chica­ must emit infrared radiation that we between the "planet" and satellite. I go, who determined that the water's oxygen isotopes may one day detect with an astro­ use quotes because, in my own were different from those in the rocky silicate por­ 'nomical satellite-if the knowledge view, Pluto may better be regarded tion of the meteorites. This suggests that the source isn't already sitting in the data bank as a large asteroid or cometary body of the water could have been the martian atmo­ of the old Infrared Astronomical than as a true planet, since it is even sphere, an ancient martian ocean or even a comet Satellite. smaller than our Moon. Spins and that hit the planet, according to Gibson. Most SET! programs have looked axial tilts of asteroids and comets The lack of homogeneous oxygen isotopes on for radio waves, but some others have been somewhat randomized by Mars also supports the theory that the planet does have searched for other clues such collisions, gas jet emissions and, not have plate tectonics like those on Earth, because as infrared or visible light pulses. perhaps, other effects. this process would have mixed the different isotopes The searches usually concentrate on -WILLIAM K. HARTMANN, together. beacons-signals deliberately meant Planetary Science Institute -from Space News 21 Mars Team T-Shirt Fill Show your support for the Mars Team! Our distinctive, 100"10 cot­ ton T-shirt sports a Your red-and-gold design depicting the Mars Balloon flying above the planet's surface, House with The Planetary Society-designed SNAKE guide-rope at­ tached. 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For information o n international shipping please call 1-818-793- 1675. Officers of The Planetary SOCiety contribute to the SOCiety the royalties due them os authors of the books advertised in these pages. Saturn's largest moon, Titan, is a world rich in methane-a gas that may have played an important role in the origin of life on Earth. Some scientists believe that a giant ocean of liquid hydrocarbons lies on the surface of this smog-shrouded moon. Others think it is divided into myriad lakes and pools. Whatever the case, these bodies of liquid hydrocarbons could harbor billions of years worth of complex organic molecules produced in the satellite's thick atmosphere. In "Titan Floating Probe, " a tiny, robotic, paddle-wheeled steamship explores the seas of Titan. Native hydrocarbons and an onboard supply of oxygen make up its fuel . . Titan and Earth have enough chemistry in common that it is essential that we go back for a better look.

Ron Miller is a Fellow of the British Interplanetary Society and a member of the International Academy of Astronautics. He is illustrator and author or coauthor of mpre than a dozen books, including The Grand Tour, In the Stream of Stars and the recent History of Earth, as well as the forthcoming Dream Machines: A Pictorial History of the Spaceship in Art, Science and Literature.

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