On the Cover: Volume XVI Comet Hyakutake provided the best celestial show in Table of Number 4 decades when it passed by Earth on its way to s.wing arou nd the Sun . In late March and earl y April , th e comet Contents July/August 1996 grew so bright that it was even visible in the light ·polluted skies of major cities in the northern hemisphere. Th is photograph, however, was not taken in am ajor ci ty; the comet appears over Kenai, Alaska, whe re the city lights Features barely dimmed the comet's glowing tai l. Millions of people around the world who rare ly glance at the night sky were 4 Belize: Rosetta Stone of the KIT Boundary enraptured by the unexpected visitor. With luck, their Between the Cretaceous (K) and Tertiary (T) periods of geologic history, something interest wi ll be captured again next spri ng, when comet catastrophic happened-and the dinosaurs disappeared from Earth. In a continuing series of Hale-Bopp-wi th the potential to be even brighter- expeditions, The Planetary Society is investigating this turning point in evolutionary history. flies through our neighborhood. Photo: Bill Hutchinson 6 Geology and Climate Change: Mechanisms of Extinction What horrific processes could have wiped out over half the species living on Earth? The team members find evidence pointing to possible suspects and eliminate others. Froln 7 Impact Processes: Reconstructing the Events The What would you have seen if you'd been watching (from a safe place) the KIT object hit Earth? This article will give you an idea of what it would have been like. Editor 8 Mineralogy: Carved in Stone Sometimes crucial evidence is found in the tiniest details: in this case, in the types lanet Earth has never been a focus of rocks, how they formed and what they are made of. P for research at The Planetary Society. Countless other organizations 10 Stratigraphy: Layers of Evidence devote their energies to the fragile envi­ The rocks blasted out by the KIT impact eventually fell back to Earth. Their final ronment that makes this planet unique. sequence and position can tell us much about the aftermath of impact We have concentrated on an area where we could make a difference: on the 12 Cornet Hyakutake: A Very Pleasant Surprise exploration of planets beyond our own. Sometimes we don't see comets until they are almost upon us. This surprise visitor But an extraterrestrial perspective is provided a magnificent show for nearly everyone on Earth. crucial to understanding Earth and the Why Near-Earth Objects? teeming life-forms that make it unique. 14 NEOs, or comets and asteroids that pass by Earth, would seem on first glance to One particularly vexing mystery about be unimpressive members of the solar system family. But they are crucial to understanding life, in fact, could not have been solved the history- and future-of the more prominent planets, including Earth. without that perspective: the extinction of the dinosaurs. Most scientists now implicate an aster­ Departlnents oid in that extinction, and that link has brought The Planetary Society into this 3 Members' Dialogue research arena. We've undertaken a series of expeditions where members can work 15 World Watch alongside scientists. This project fulfills NelNs and RevielNs two of our goals: to advance science and 16 to involve our members personally in that 17 Society NelNs adventure. Here we report the results of the latest expedition. Later this year, a 18 Basics of Spaceflight: Electrical Systems team goes to Gubbio, Italy, where scien­ tists found the first evidence linking an 20 Questions and AnslNers asteroid to the dinosaurs. Join us as we . unravel the mystery of the dinosaurs' demise, either by reading these pages or by joining an expedition. Either way is a Contact Us unique benefit of Society membership. Mailin g Add ress: The Planetary Society, 65 North Catalina Avenue , Pasadena, CA 91106-2301 -Charlene M. Anderson General Calls: 818-7 93 -5100 Sales Calls Only: 818 -793-1675 E-mail: tps @genie.com World Wide Web Home Page: http://planetarY.org/tps/

r:a~~~~~~ZAR~ff~~~~1?~~~~§~S~~~lii~:~a~~rgf;\~IYm~~~e~~ i~~r~a~~~~e;e~!~h~~~~~~~~~~'~~~e~9nNt~~huCsa~~~n:2~venue , (US dollars); in Canada, $35 (Canadian dollars). Dues in other countries are $40 (US dollars). Printed In USA. Th i rd~class postage at Pasadena, California, and at an additional mailing office. Canada Post Agreement Number 87424. A ....~.~.. Ii Editor, CHARLENE M. ANDERSON Technical Editor, JAMES O. BURKE THE-PLA~TfRV SOCIETY Assistant Editor, DONNA ESCANDON STEVENS Copy Editor, GLORIA JOYCE Production Editor, MICHAEL HAGGERTY A~t Director, BARBARA S. SMITH o .~ -e- ¢ -B- 0 Viewpoints expressed in columns or editorials are those of the authors and do not necessarily represent positions of The Planetary Societ y, its officers or advisors. © 1996 by The Planetary Society. o Board of Directors CARL SAGAN President Dlrectcr, Laboratory tor Planetary Studies, Members' Cornell University

BRUCE MURRAY Vice President Dialogue Professor of Planetary Science, California Institute of Technology

LOUIS FRIEDMAN Executive Director

NORMAN R. AUGUSTINE President, LockfJeed Martin Corporation

JOSEPH RYAN Executive Vice Presiden t and General Counsel, Marriott International

STEVEN SPIELBERG director and producer

LAUREL L. WILKENING SET. Debate high intelligence has arisen methodologies. However, so Chanceffor, University of California, Irvine

I would like to contest Ernst only once on our planet. How does he- in his application of Board of Advisors Mayr's conclusion that high many times need it have arisen probabilistic analysis to a bio­ DIANE ACKERMAN poet and author intelligence is rare and not to qualify as significant? He logical system. For example, he BUZZ ALDR IN favored by natural selection. also asked how survivors of ear­ points out the fragility of the Apollo 11 astronaut RICHARD BERENDZEN The fossil record shows that, lier impacts would be selected chain of evolution that resulted educator and astrophysicist over time, organisms as a whole to develop the technical know­ in Homo sapiens. He also men­ JACQUES BLAMONT Chief Scientist Centre National have grown more complex, how to prevent future impacts. tions the astronomical number d'£tudes Spatiales, France RAY BRADBURY more organized and largely The idea is not to be selected of species that failed to achieve poet and author more intelligent. I'm not sure after the last impact, but to be high intelligence. Yet, probabilis­ ARTHUR C. CLARKE author how to measure the "average" selected before the next one. tically, it is that very proliferation CORNELIS DE JAGER Professor of Space Research, intelligence displayed in the One of Sagan's final respons­ of false starts that increases the The Astronomical Institute at Utrecht, ecosystem, but I am pretty sure es was that Mayr conceded that likelihood of a fragile chain the Netherlands FRANK DRAKE Professor of Astronomy and Astrophysics, that it has increased tremen­ there may be extraterrestrial eventually surviving. University of Califomia, Santa Cruz dously over the past 100 million intelligence. It seems to me that His strongest point against JOHN GARDNER years. Extrapolating this trend he is just flat wrong in saying SETI was the unlikelihood of founder, Common Cause MARC GARN EAU of increasing intelligence would that. While reading Mayr's our civilization aligning in time Canadian astronaut GEORGIY GOLITSYN suggest that it is not at all discourse, I never once got with another so we are listening tnsti'tute of Atmospheric Physics, unlikely, but is favored by nat­ the impression that he didn't at the moment they are broad­ RussIan Academy of Sciences THEODORE M. HESBURGH ural selection and will arise, believe that extraterrestrial casting. True. But an advanced President Emeritus, University of Notre Dame given enough time .. intelligence exists, merely that civilization might plant beacons SHIRLEY M. HUFSTEDLER Rather than seeing us as it is improbable. able to broadcast for thousands educator and jurist GARRY E. HUNT unlikely, I think that we are -RUSSBAIN, or millions of years, long after space SCientist, United Kingdom SERGEI KAPITSA simply the first highly intelli­ Glendora, California their "short-lived" civilization Institute for Physical Problems, gent creatures on Earth. had perished. Russian Academy of Sciences GEN. DONALD J. KUTYNA (RET.) - E. MARC COE, Mayr points out that "perhaps Of course we cannot guaran­ former Commander, US Space Command Brick, New Jersey 50 billion species" originated tee success by searching, but JOHN M. LOGSDON Director, Space Policy Institute, on this planet, with "only one" we can guarantee failure by not. George Washington University HANS MARK I just finished reading the evolving to civilization. He - TERRlLL L. BURLISON, The University of Texas at Austin debate on SETI between Ernst should have stated "only one, so Kent, Washington JAMES MICHENER author

Mayr and Carl Sagan. I noticed far." A scant 65 million years MARVIN MINSKY T(}Shiba Professor of loopholes in both arguments. ago, our ancestors were but ERRATUM: The photo caption Media Arts and Sciences, Mayr said that out of 20 civiliza­ primitive mammals. There are on page 12 of the March/April Massachusetts Institute of Technology PHILIP MORRISON Institute Professor, tions, only one has developed dozens, if not hundreds, of 1996 issue of The Planetary Massachusetts Institute of Technology the technology to send and species at least that advanced Report stating that the floodwa­ PAUL NEWMAN receive signals. Therefore it i's today. Does Mayr believe if ters flowed "more than 18 cubic actor JUN NISHIMURA unlikely that there is another · • humans are exterminated by meters (600 cubic feet) per sec­ former Director General, Institute of Space and civilization somewhere like disease or environmental disas­ ond" was incorrect. The correct Astronautical Science, Japan SALLY RIDE ours. ter none of these species will figure is about 11 million to 17 Director, Cafifornia Space fnsfitute, University of California, San Diego, Though most civilizations evolve high intelligence in the million cubic meters (400 mil­ and former astronaut ROALD Z. SAGDEEV have died off, the successful next 65 million years? And that lion to 600 million cubic feet) former Director, Institute for Space Research, ones learned from the mistakes is but I percent of the evolu­ per second. Russian Academy of Sciences of predecessors and so were tionary time left to this planet. HARRISON H. SCHMITT former US Senator, New Mexico, more advanced and more capa­ In fact, civilization evolved Please send your letters to and Apollo 17 astronaut S. ROSS TAYLOR ble of survival. Wouldn't it be exceedingly quickly, once life Members' Dialogue, Professorial Fellow, reasonable to assume that other moved onto land. We just hap­ The Planetary Society, Australian National University, Canberra JAMES VAN ALLEN planetary civilizations do the pen to be the first example. 65 North Catalina Ave., Professor of Physics, University of Iowa same? Mayr also chastises Sagan Pasadena, CA 911 06-2301 Mayr made the point that and others for misusing or e-mail [email protected] . 3 This year's expedition traveled farther from the center of Chicxulub than did the 1995 expedition. BE ZE: ROSETTA The team was able to study a wider STON OF THE range of materials blown out by the im­ KIT BOUNDARY pacting asteroid. Map: B.S. Smith

he mysteries surrounding the dinosaurs entice our the floor of the buried crater. To study the Chicxulub crater, imaginations. These magnificent creatures dominated scientists would have to undertake a systematic-and very ~the biosphere of our planet for over 150 million years, expensive- drilling program. Mexican scientists are now then came to an end 65 million years ago, with the close of carrying out such a program on a limited basis. the Cretaceous period in Earth's history. Those of us who believe in catastrophism, or abrupt change, o£# riut"E~ Co tJdiw as I do, over uniformitarianism, or gradual change, as an Another way to study the crater would be to fi~g the ejecta explanation for the end ofthe Cretaceous period, embrace the blanket- that is, the rocks ejected from the crater by the idea that a key player in this mystery came from outer space. force of the impact. If this blanket was found on the surface, The ensuing catastrophic event produced such a dramatic there would be no immediate need to drill. Fortunately, we 'change in Earth's environment that over 50 percent ofthe identified such a site in northern Belize, about 364 kilometers species living at the time, including the dinosaurs, perished. (226 miles), or two to three crater radii, from the crater. That . The first suspicion that an extraterrestrial body might have was the destination of our first Planetary Society expedition, been responsible for the dinosaurs' demise came in 1980, which took place in January 1995 (see the July/August 1995 when Luis and Walter Alvarez, with Frank Asaro and Helen Planetary Report). Michel, of the University of California, Berkeley, identified That expedition proved fruitful. Among the discoveries of the element iridium in a worldwide clay layer marking the our team of Society members and professional geologists boundary between the Cretaceous (K) and the Tertiary (T) was a new species of crab, named Carcineretes planetarius periods. Iridium is rare on Earth's surface, but common in after The Planetary Society. Like the dinosaurs, this species solar system objects such as asteroids and comets. became extinct at the end of the Cretaceous. These marine As intriguing as this evidence was, scientists favoring an crabs used to float in shallow coastal waters. Finding fossils in extraterrestrial culprit were left without the proverbial smoking the sediments exposed in a limestone quarry on Albion Island gun to clinch the case. That is, until 1990, when a crater buried in the Rio Hondo gave us insight into what the environment beneath the town of Chicxulub (pronounced chix'oo lube) in of Belize was like when the impact took place. the Yucatan peninsula was identified as the probable impact With the discovery of this new species of crab and other site of an asteroid or comet 65 million years ago. For the first fossils-for example, a type of snail called a nereid-we time, scientists had the opportunity to study a large- over 200 were able to confirm that we had indeed found material dat­ kilometers (120 miles) across- and well-preserved impact ing from the end of the Cretaceous in a surface exposure of crater. Because it has been buried under 1,000 meters (3,000 the ejecta blanket from Chicxulub in Belize. We found many feet) of sediments in a tectonically inactive region, the crater more clues to the catastrophe: tektites (droplets of glass has been protected from erosion. formed from rock melted by the impact) that matched the The main surface feature that distinguishes Chicxulub as composition ofthe target rock in the Yucatan peninsula; a crater is a ring of sinkholes (cenotes in Mayan) that marks striated boulders--one was 8 meters (26 feet) in diameter-

Seen in cross section, the Chicxulub crater might have looked something like this, with the blanket of material ejected from the crater flowing all the way to modern­ day Belize. Today, the crater itself is buried under hundreds of meters of sediment. Chart: B.S. Smith

4 The team traversed a landscape that looked like a Hollywood fantasy of a jungle. Above, team members prepare to explore a cave. At left, they canoe down the Macal River, where they discovered possible KIT exposures. In the center is a magnificent fold in Tertiary limestones. Photos on this page: Adriana Ocampo and Kevin Pope

scarred as they were blasted out with tremendous force; and the impact. But there is much yet to be understood about them. hinged pebbles (also called fracture pebbles) fOlmed by a Pook's Hill is over five crater radii away from Chicxulub, and combination of plastic and brittle defOlmation caused by the impact models tell us that such features should only be found explosion. All these confirm that the deposits in northern closer to the crater. We might still be on the ejecta blanket from Belize must have been produced by something as tremendously Chicxulub, or we might have found the ejecta blanket from a violent as an asteroid or comet impact. secondary crater. In the style of a well-developed detective story, Belize is t(/e ~ ae J'eMd showing us that we know very little about large impacts and With this evidence in hand, we decided to find out how far the how they might affect our biosphere to cause a mass extinction. ejecta blanket extended in Belize, in the hopes of finding more But the clues are there. With every sample that Planetary clues to large impact crater processes. This proved to be very Society team members brought back from Belize, we are challenging, since in this tropical area rocks are rare, but gaining a greater understanding of Earth, its biosphere and beautiful and lush vegetation is plentiful. Our search led to the planetary evolution. second Planetary Society Belize expedition, in January 1996. We began our work in the limestone quarry on Albion Island, Adriana Ocampo is a planetary geologist at the Jet Propulsion and then extended our reach to the Cayo district of central Laboratory in Pasadena. This research is funded by NASA 's Belize and the foothills of the Maya Mountains. Exobiology Program and The Planetary Society. Some ofthe most puzzling things that we found were rounded limestone pebbles with highly polished surfaces marked with striations or grooves. We affectionately called them Pook's pebbles, since they were first found in the jungle on Pook's Hill, near Teakettle village in central Belize. Their origin and how they were deposited there are still the subject of much of our research. We believe that they are related to the impact, and that they were deposited via debris-flow mechanisms triggered by

One of the team's favorite spots was Pook's Hill, location of one of their "hotels" and some peculiar pink pebbles that seem to have been altered by impact processes. At bottom right is the jungle side of the hill; on the top right is the rocky side, where the Pook's pebbles were found. (For a close-up of one of these pebbles, see page 9.)

Within this fragment of dolomite is a well-preserved Late •• Cretaceous crab, named Carcineretes planetarius in honor of The Planetary SOCiety. • EC •

Based on evi­ N WARM dence collected FIREBAll by Planetary Vaporized Society expedi­ out-ol-footprint material tions and oth­ HOT FIREBAll ers, this chart Vaporized shows some of projectile and the effects of footprint the Chicxulub material impact that he giant meteorite impact that formed the Chicxulub might explain crater was one of the largest in Earth's history. Only the rocks so Sudbury crater in Canada and Vredefort crater in far uncovered. r (The "foot­ South Africa are perhaps as large. It is difficult to study a print" is the Debris flow __.._ crater like Chicxulub, which is deeply buried by sediment, so target rock directly within we chose to look for other evidence of the impact that killed BELIZE the path of the I I I the dinosaurs. In Belize, we found rocks ejected from the projectile.) Okm 200km 360 km crater preserved at the surface. These exposures of ejecta Chart: B.S. Smith deposits are the closest known to the Chicxulub impact site. The tremendous size of the Chicxulub impact, the proximity of Belize to the crater, and the excellent preservation ofthe released as heat that it instantly vaporized rock. Computer ejecta deposits found in Belize make this Planetary Society models suggest that the Chicxulub impact would have research unique among impact crater studies. vaporized rocks within 6 to 12 kilometers (4 to 7 miles). One of our most exciting discoveries was that the ejecta These rocky vapors were composed of trillions of tons of contained millimeter- to centimeter-sized spherical bodies sulfur dioxide (S02) gas, carbon dioxide (C02) gas and water (spherules) of carbonate rock. Some of these spherules are (HP) vapor once peacefully contained in a 3-kilometer­

made of the mineral calcite (calcium carbonate, CaC03) , thick (2-mile) layer of carbonates and sulfates at the impact which forms fiber-like crystals radiating out from the center site. Superheated to thousands of degrees Celsius, these gases of the spherule. Others are made of the mineral dolomite expanded rapidly, eventually encircling Earth.

(calcium magnesium carbonate, CaMgC03), which commonly Many scientists believe that these gases, along with soot forms concentric bands of large and small crystals around and dust ejected into the atmosphere, caused climate changes fragments of dolomite rock. Where did these strange balls of that ultimately helped kill off over 50 percent of the living rock come from? Our current hypothesis is that they formed species following the impact. Especially lethal was the sulfur

as material within the expanding plume of rock vaporized dioxide, which formed sulfuric acid (H2S04 ) clouds in the by the impact condensed and coagulated into larger paliicles. stratosphere. These clouds could have blocked sunlight, pre­ The spherules ultimately fell like hail on Belize. venting photosynthesis for a few months and cooling Earth's surface to near freezing for about 10 years. In addition, the /? Lethd Pktne sulfuric acid production would have depleted ozone (03) The vapor plume rising over the Yucatan landscape 65 mil­ and also would have led to years of severe acid ~ain. lion years ago must have been an awesome sight. When the Another proposed cause of the mass extinctions is green­ incoming asteroid or comet struck, so much energy was house warming from carbon dioxide released by the impact, although recent impact models indicate that this warming was probably less than a couple of degrees Celsius. Further­ more, our discovery of carbonate spherules in Belize suggests that some-perhaps much-of the carbon dioxide vapors did not reach the stratosphere. Instead, these vapors combined with particles of calcium oxide (CaO) or magnesium oxide (MgO) that had also been carried aloft in the plume. They coagulated into carbonate particles and fell. If this proves correct, then greenhouse warming can be exonerated as the cause of the mass extinctions at the end of the Cretaceous period. Impact "winter" caused by the vaporization of sulfate rocks remains the favored theory. These calcite spherules show dramatic evidence of the unusual processes that shaped them. Above are the rounded forms taken by the vaporized or Kevin Pope is a geologist who has worked in Belize for over molten rock as it cooled and crystallized. At the right is a close-up of the crystals showing the radial growth form, which tells us they grew rapidly. 10 years. His studies ofthe climate effects ofthe Chicxulub 6 Photos: JPUNASA impact are supported by the NASA Exobiology Program. 1--· E EVE

Left: Mike Rampino scrapes away at an ejecta blanket exposure in Cristo Rey. Below: This weathered expo­ ixty-five million years ago, an asteroid or comet sure gives a good view of the 10 kilometers (6 miles) in diameter, traveling at KIT boundary. At the bottom between 20 and 60 kilometers (roughly 10 and 40 is the Late Cretaceous Barton S Creek dolomite. Just above miles) per second, slammed into what is now the Yucatan the pen is a spheroid bed of peninsula of Mexico. The result was clearly a global catastro­ rounded rocks formed in the blast, and on top of that is phe. The impact energy (equivalent to the explosion of 100 the ejecta bed. trillion tons of TNT), which was converted into shock waves Photos on this page: and heat, blasted a giant impact crater and hurled massive Adriana Ocampo and Kevin Pope amounts of melted, fragmented and vaporized rock into and above the atmosphere. Upon atmospheric reentry, this debris was heated to such an extent that Earth's surface became a broiler, igniting forests worldwide. The sky went dark as the dust and soot slowly set­ tled on the burnt landscape. In the Gulf of MexicolCaribbean region, the impact set off destructive earthquakes and tremen­ dous tsunami waves, washing away entire coral reefs and sweeping low-lying coastal areas clean. The aftermath of the impact may have included a global cloud of sulfuric acid droplets, blasted from the target rocks at Chicxulub, that cut down incoming sunlight and cooled Earth for decades. Not surprisingly, when the dust cleared, most of the species oflife on land and in the sea, including the dinosaurs, were gone. This remarkable story has been pieced together through a combination of extensive geologic fieldwork, carefully executed laboratory analyses and sophisticated computer modeling. The decade and a half since the discovery of impact evidence by the Alvarez group has seen a steady confirmation of the impact scenario, with scientific sleuthing that culmi­ nated in the location and dating of the Chicxulub crater just a few years ago by several groups. S'tium44R~ The Planetary Society's expeditions to Belize have provided a unique look at the by-products of one of the most dramatic processes set in motion by the massive impact-ballistic de­ bris flows. During the impact, fragments ofthe target rocks were splashed upward and outward from the crater at high velocity. This debris traveled in arcing paths, eventually falling back to Earth. Imagine a curtain of such debris, sweep­ ing rapidly outward from the impact site, violently striking the ground, tearing up the surface rocks and moving outward as a ground-hugging flow of mixed ejecta and local rock. Such storms of rock would have leveled everything in their paths, burying the countryside under tens of meters of debris, until finally the flows ran out of steam hundreds of kilometers from the crater. The Belize localities are the closest that scientists can get to the Chicxulub crater to study the ejecta without having to drill through a thick ~over of younger rocks. What we found /J AJeed to R~ there-chaotic deposits of fragmented rock showing clear Moreover, these unusual deposits may have a significance signs of rapid flow and containing strange boulders and that goes far beyond the events at the Cretaceous/Tertiary cobbles showing marks of violent collision, smooth facets, (KIT) boundary. Similar deposits occur in the geologic striations and a mirror-like polish-told us that we had hit record, and they have been interpreted as the products of the jackpot. During the 1996 expedition, we spent two ancient glaciation primarily because ofthe presence of weeks climbing over some of the most unusual deposits large boulders and scratched and polished stones resem­ on Earth, collecting samples, recording data and happily bling those found in deposits of the most recent ice age. arguing about what it all might mean. The discovery that impact debris can have analogous We have compared our samples from the Chicxulub features casts doubt on the interpretation of some of debris flows with the debris of other known impacts, such these deposits as glacial in origin. In reality, they may be as that ofthe 3D-kilometer-diameter (19-mile) Azuara impact debris, or the products of debris flows generated impact structure (about 35 million years old) in Spain and by other violent processes. Further study of the Belize the 26-kilometer-diameter (16-mile) Ries impact structure material and other known impact debris will enable (15 million years old) in Germany. There are remarkable geologists to develop better criteria for distinguishing similarities, although the scale of the Chicxulub deposits impact ejecta from true glacial deposits in the geologic is so much larger. It will take considerable laboratory record. analyses and additional fieldwork in Belize to unravel the origin of the features that we observed, and the information Michael Rampino is an associate professor in the Earth gained from our studies will help in creating computer sim­ and Environmental Science Program at New York Uni­ ulations of the violent processes by which these materials versity, and a consultant at NASA's Goddard Institute for are ejected from impact craters. Space Studies in New York City.

• E ~L • E

e members of The Planetary Society's 1996 expedition to Belize have delightful memories riof fascinating landscapes, interesting people and fellowship-and the tantalizing problems involved in trying to interpret rocks in the field. Here I write about the aftermath ofthe expedition, getting at the story of what happened after the Chicxulub impact by working on the Belizean rocks in the laboratory. We have a long way to go before the story of what happened there is complete, but some things (and some questions) have been clarified. We now have no doubt that the deposits we studied, from The rocks cal/ed hinged pebbles (see page 5) proved particularly interesting. around the Cretaceous/Tertiary boundary in the Albion Island The force of impact seems to have cracked them, healed the crack, encrusted quarry in northern Belize, and in the flanks of the Maya and then polished them before they came to rest in the ejecta blanket. Similar Mountains in central Belize, contain ballistic ejecta- that is, rocks are found at other, weI/-studied impact sites. Photo: Adriana Ocampo and Kevin Pope material blasted out by the force of the impact. At Albion Island, we found clay shards containing relict vesicles­ holes left by gas bubbles formed while the rocks were melted. but tangible evidence of an impact origin, other than glass, These shards are surely altered glass, most likely derived had been tenuous. By the end of our 1996 visit there, we from the Chicxulub impact. had found, in a layer we interpret as the ejecta blanket from The 1995 Planetary Society expedition provided evidence the Chicxulub impact, two rock specimens that provided that Albion Island had been land at the time of the impact, more solid evidence. probably an island much like the Bahama Islands, which are emergent parts of the Bahama Bank. We were able to velify AJew lJata rMSWn AJ~ 8etf/;e that the deposits exposed in the Albion Island quarry were One specimen from the Albion quarry is a small, steeply near 65 million years old and corresponded at least roughly conical piece of dolomite, with a fan of striations radiating 8 to the boundary between the Cretaceous and Tertiary periods, out from one side of its pointed top. This resembles shatter cones, structures found in rocks surrounding meteorite impact sites, though it lacks the "horsetail" structure of striations in typical shatter cones. Furthermore, near its top this specimen has embedded within it angular chips of another kind of dolomite that penetrated it, plus the tracks of other chips. At some stage in its history, this rock had the consistency of putty, allowing other rock chips to become embedded in it. Did this happen under the enormous pressures generated during the initial stages of ejection? Or did it happen in a micromoment when intense shock broke the molecular bonds and turned the dolomite rock into a tough jelly? The other specimen, also fi'om the Albion quarry, is a piece of red chelt (flint), a rock nOlmally composed of micro granular crystals of quartz. When viewed in thin section under polarized light, this chert is found to be an interlocking mosaic of spherulites, bodies composed of fibers of quartz (chalcedony) radiating out from the center. That is the struc­ ture formed when a glass, such as obsidian, crystallizes rapidly. Here the chert was, for an instant, turned into silica glass by a shock that completely disrupted the molecular bonds. It rapidly recrystallized into spherulites by radial growth of chalcedony fibers from randomly scattered "seeds." Similar but larger spherules of calcium carbonate previously found in the Albion quarry had initially been interpreted as accretionary, pea-sized globes of limestone called "pisolites." These are now viewed as formed by recrystallization of lime­ stone, most likely in response to shock-melting. We thus have every reason to think that these specimens were blasted out of an impact crater on a ballistic trajectory, and then became incorporated into a debris flow that carried them some additional distance. It seems likely that they came fi'om the Chicxulub crater some 350 kilometers (200 miles) to the north. A remaining question concerns the blocks of ordinary dolomite in the layers we consider to be part of the ejecta blanket thrown out by the impact. These do not reveal such evidence of intense shock, but many are marked with facets and striations (grooves). How many of these were blasted out of the crater, and how many were merely swept up by the ejecta blanket as it rushed over the Yucatan region? Did the faceting and striations occur as the rocks were flying out of the crater, or were they cracked and grooved as the mass of debris flowed across the countryside? We also have ques­ tions about the matrix of the sedinlentary layer that we be­ lieve to be the debris flow: Did this dolomite crys4111ize out of the cloud of vaporized rock thrown up by the inlpact, or is it merely soil that had accumulated over the Yucatan region, and rock ground up during transpolt? lJi4aweUe4 ~ ~ tldVJe During the 1995 expedition, Adriana Ocampo and Kevin Pope had found in central Belize, on the nOlth flank of the Maya Mountains, a sedimentary layer containing polished From top: This conical piece of dolomite (a) with striated faces pebbles and cobbles. They suspected it might be part of the seems to be a shatter cone, a rock typically found surrounding impact sites. (Scale bar on rock is 1 centimeter in length.) ejecta blanket thrown out by the Chicxulub impact. Here the The expedition team found beds filled with glass spheroids 1996 expedition gathered a rich harvest. (b) formed by the shock and heat of the impact explosion. This pink rock (c) is a Pook's pebble, named for its discovery These are rounded pieces oflimestone and marble, rarely site. Its beach-worn look is the result of impact processes, as dolomite, containing some chert nodules. They superficially evidenced by the impact pit in its side. (Scale bar on rock is resemble stream-rounded or beach-worn cobbles and pebbles, 1 centimeter in length.) Pook's Hill was also the site of mud balls-matrix-coated but many of them have flat and commonly striated facets, boulders (d) wrapped in finer material before being deposited rounded hollows, and deep pockmarks. Some have been split among the impact debris. Photos: Adriana Ocampo and Kevin Pope 9 and displaced along the fracture, and most have been polished dolomite. In the central region, the ejecta are limestone and in places. These rocks' include tan limestones-lithified marble in a matrix ranging from drab or red clay to limestone. shallow-water carbonate sands that retain their original shell Altered glass, common in the deposits in northern Belize, is fragments, accreted ooids (tiny, rounded carbonate rocks), rare or absent in central Belize. and the microscopic skeletons of planktonic animals and Were these deposits derived from the same impact crater? algae. But the more battered ones have recrystallized into We know from images of Mars and other bodies that several marbles with crystal sizes diminished from those in the lime­ lobes can be ejected from a single crater, and our observations stones- the process of mosaicism associated with shock. would imply that such lobes result from different domains Growth of radially structured spherulites, both in the carbon­ and stages of ejection. An alternative explanation is that the ate and in the cherts, repeats the pattern found in the Albion ejecta of central Belize came from separate impacts, most quarry-crystallization from patches that melted under shock. likely related to Chicxulub. Either the impactor had broken As yet we have no precise data on when these limestones into pieces before striking Earth, or a large mass ejected by were first laid down. Once we have properly prepared a suitable the primary impact fornled a crater of its own. amount of well-preserved fossils, we can begin paleontological We can answer some of our questions with further labora­ studies to fix their age. The pebbles and cobbles bear evidence tOly study, now being carried out with the help of NASA. of shock and ballistic transport, but we have much to learn Other questions will no doubt emerge. In the meantime, we about the conditions that shaped them. Mineralogical and are delighted to pass along this candid progress report, with compositional investigations may give us more definitive gratitude to the ever-enthusiastic members of our expedition evidence of the pressures and temperatures these rocks en­ and to The Planetary Society. countered. Further studies will clarifY the sequence of events. Alfred G. Fischer, long associated with Princeton University, is now professor emeritus ofgeology at the University of ~~hat puzzles us is the difference between the Southern California in Los Angeles. His studies have focused deposits we found in nOlthem and central Belize. In the north, on the history ofthe outer Earth in terms of the interactions the matrix of the layers and the ejecta are mainly drab-colored between physical and biological processes.

SM ~p Y: ~YE s E D CE

n the foothills of the Maya Mountains, and in the Cayo district of central Belize near Belmopan, the ~capital of Belize, Planetary Society team members studied a sedimentary layer 30 meters (100 feet) thick. We believe this layer to be a remnant of the debris ejected by the impact that ended the dinosaur era. Whatever the mechanism, or the exact sequence of events, it's staltling to imagine how such a thick blanket ofrock could be laid down over such a vast area-the Yucatan peninsula and adjacent parts of Central America - in such a brief time. Calculations show that the debris flow from the Chicxulub crater would have moved at about Most of the boulders the team examined in the KIT layer during the 300 meters (1,000 feet) per second. That puts its arrival 1996 expedition came from local bedrock. But the polished boulders time in Belize at only 15 to 18 minutes after the impact. in the center are not from Belize. They seem to have been blasted out Few locales on Earth afford the opportunity to study such from somewhere else and carried to Belize by the impact. a massive, rapidly deposited body of rock. The layer we Photo: Adriana Ocampo and Kevin Pope examined lies between a bed of Late Cretaceous Barton Creek dolomite and the overlying Early Teltiary El Cayo Group To gain an internal view of this layer, we constructed a carbonates. To study this boundary layer, we measured 21 cOlTelation among the 21 sections (Figure 2). A glance at stratigraphic sections (Figure 1, page 11) to determine the the correlation shows that individual beds appear in all the nature and sequence of the rock layers. Thirteen sections stratigraphic sections. There are as few as five to perhaps 10 spanned the ejecta layer. as many as 10 beds in any given part of the layer. Figure 1 North similarities of materials within A 89°W Figure 1: the beds suggest that a common BELMOPAN Measured stratigraphic process formed each one. Third, sections in the strata within the debris flow the Cayo dis­ suggest that the separate layers trict, Belize, SAN •• were (1) moving at different IGNACIO : ... MH2• All sections ~ are located by •• ••• CRl speeds, (2) following different .. °0 Ingbird, HighwaV a dot, except ee2 •••• MR1 the Maca/ paths, (3) deposited at different ee1 ••:. ~3 River section times or (4) generated from NM~· I:: MET• (MR1), which different locations. SAl• NM2 \ is along the 1:350,000 river (dotted All this makes it certain that, ..... o 5 10 15 20 kilometers .. t \ \I! i I I line) between whatever happened after the the black !... ______~O ____ ~5_m~e~ !.!0!l ______triangles, asteroid struck the Yucatan, the I materials that were blasted out followed yet-to-be-understood Figure Z paths to their final resting places. It is possible that secondary SOUTHWEST CSl NORTHEAST _110m NMl Figure 2: impacts of rock blasted out of the C2 This chart PHl - 100 original crater played a role in D gives the 0 - 90 correlations determining the final stratigraphy among the CRl MH2 of the ejecta layer. Large boulders - 80 21 measured sections, blasted out by the impact may ""' 0 - 70 Bedding have rained down on Belize in a I~rn PH' PH2 MH1 MH3 D contacts are UPPER DAT~M et3 _ 60 sort of carpet bombing. This may o 0 0 indicated by HHl explain why the flow deposits ~ NMZ 0 • lines drawn i!llii - 50 c> across the contain so much local rock, and ~j • D:. - 40 section why they appear to have come column (e,g" LOWER DATUM 0 - 30 there are from different directions at four beds in 'j _ 20 different times. '0 section MR1). o From our study of ejecta ... _10 u. Charts: blankets, we hope to learn more c O. T. King, Jr.; r------rl------,.-Om redrawn by about how the impacts of objects .,~ 10 20 km B.S. Smith from space have shaped the face

BOULDER TYPES: 0 TAN DOLOSTONE • BOULDERS WITH BEDDING 6. RAUHWACKE of Earth. As this is the largest ~ POLISHED PINK o BRECCIA·IN·BRECCIA • COATED impact event known in the inner solar system with an age less than 3 billion years, it is a potential source of useful information 1Jt~ the SecU about much older terrestrial impacts and their ejecta layers. Each bed has both common and distinctive characteristics. Similar internal stratigraphy of ejecta blankets may eventu­ Beds range from 3 to 10 meters (10 to 30 feet) thick, and ally be encountered on geological expeditions to Mars, the thickness can vary along a single outcrop, The rocks making up the beds, from the finely ground matrix to David T King, Jr., is an associate p rofessor ofgeology at boulders 8 meters (26 feet) across, are poorly sorted. Many Auburn University in Alabama, His specialty is stratigraphy, of the beds show evidence of flow lamination- thin, and he also researches dinosaurs and the KIT boundary. parallel layers of sediment indicating laminar rather than turbulent flow conditions- in their upper third. We found six main types of boulders: tan dolostone The expedition boulders, boulders with bedding (these had internal team paused stratification or beds), matrix-coated boulders, rauhwacke for a tour of a ("rough-rock") boulders, breccia-in-breccia boulders (these conservation area given by J' large blocks contained angular fragments of limestone and the director dolostone) and polished pink carbonate boulders, The first of the Belize Zoo (center, five types come from the local Late Cretaceous bedrock. back row), The polished pink boulders do not seem to come from Photo: Belize. They may have been blasted out in the impact and Adriana Dcampo's carried to Belize along a suborbital trajectory. camera From our studies of the beds and the materials within them, we suggest several conclusions. First, the textures and sedimentary structures within each bed are consistent with some type of debris-flow deposition. Second, the 11 By piecing together high-resolution images of the comet, astronomers at the University ot and all the streams, kinks and knots typical of a cometary tail are easily seen. For exampl disconnection event, where a piece of the tail appears to have broken off the'nucleus. Scil a gust in the solar wind, but images from the Hubble Space Telescope showed that a fragl this may have caused the disconnection event. (The spiral galaxy M101 also appears in tf; one of ionized gas or plasma and one of dust. The dust tail on this comet was hardly notic This mosaic covers the width of 60 full Moons, showing what an impressively large objem Mosaic: James M, De Buizer and James T. Radomski, with R. Scott Fisher and Robert Pina, University ( urprl-

The comet appears very differ­ ent in this image taken by the European Southern Observatory's New Technology Telescope in La Silla, Chile. Here the focus is on the inner coma of comet Hyakutake and on the jets of dust spewing from its relatively tiny nucleus at the center of the image. The nucleus' rotation is also apparent as the jets curve in response to its motion. The dust is freed from the frozen nucleus as the comet heats up as it nears the Sun. The stream of ionized particles flowing from the Sun, known as the solar wind, "blows" the dust in the New technologies are changing the way we see comets and anti-solar direction, creating the other celestial objects. This image was taken with a reflector bright tail easily seen from Earth. telescope-a technology a few centuries old. But instead of Image: Olivier Hainau~ Richard Wes~ a human eye recording the comet, in this case a camera Manuel Pizarro and Vicente Reyes, using charge-coupled devices produced this image. Three from the European Southern Observatory 60-second exposures were added together, and then a computer processed the image to bring out the dust jets streaming from the comet. No naked human eye ever saw a comet this way, but with these new technologies, we can now view these objects in many different ways. Image: Tim Puckett

A quiet pond reflects bright stars and the planet Venus as comet Hyakutake sinks into the glow of Kansas City. The constellation Orion appears to the left, Venus to the left of center and the comet to the right of center. Photographer Vic Winter took this beautiful shot while standing knee-deep in mud as the temperature dropped into the vicinity of 30 degrees Fahrenheit Photo: Copyright 1996 Vic Winter 1I

hy. I:arl Sag.an • The dinosaurs and 75 percent ofthose species then on Earth seem to have been rendered extinct by the impact of a There's more than the thrill ofdiscovering new worlds to 10-kilometer-diameter (6-mile) NEO some 65 million years justify our exploration ofthe solar system. There are solid ago. The Tunguska event of 1908 in Siberia, the recently scientific-and often social and political-reasons for un­ declassified United States Air Force data on small objects dertaking such difficult and expensive endeavors. But these entering Earth's atmosphere, and particularly the impact reasons are not often pulled together to increase the force of some two dozen fragments of comet Shoemaker-Levy 9 ofour advocacy for planetary science. NASA Administrator with Jupiter all underscore that dangerous impacts may occur Dan Goldin asked Planetmy Society President Carl Sagan today. The best estimate ofthe probability of a civilization­ to do just that to help him make the case for studying near­ threatening collision in the next century is nearly one in a Earth objects (NEOs). Here are Dr. Sagan's points. thousand. -Charlene MAnderson • A program to inventory aU large NEOs is needed to deternune not only orbital elements but also something of • A population of some 2,000 small worlds more than the physical and chemical properties of the inventoried 1 kilometer (0.6 mile) in diameter orbits the Sun very near NEOs. Ground truth on the NEO is needed to calibrate re­ Earth. Some have arisen from the main asteroid belt; others mote observations. Transponders may have to be emplaced are dead or dying comets deriving ultimately from the outer on potentially dangerous NEOs. solar system. Most NEOs are gravitationally perturbed into • The population ofNEOs probably ranges from highly and out of near-Earth orbits on timescales of 10 million to coherent objects to weakly cohesive fluffbal1s. If the time 100 million years. ever comes when it is necessary to deflect or disintegrate a • NEOs therefore represent a convenient opportunity to NEO on an Earth-impact trajectory, it will be essential to have study small worlds at much less cost than missions beyond in situ experience with the various populations ofNEOs. For Mars orbit. example, the coupling constant in the use of standoff nuclear .NEOs present fairly pristine samples of the early weapons may be highly variable from NEO to NEO. planetesimals that built the planets-with clues to conditions • The dangers presented by NEOs over the next century in the solar nebula from which the solar system formed. probably provide another coherent justification for the de­ Some NEOs have undergone more physical and chemical velopment oflong-duration human spaceflight capability. processing than others. Some NEOs are easier to get to than the Moon. Some • The dumbbell shape of some NEOs (e.g., Toutatis) round-trip missions to interesting NEOs with as much as a raises the intriguing possibility that we are seeing here rem­ 30-day stay time on the NEO surface take less than a year. nants of the accretion of planetesimals, and therefore the In general, missions to NEOs are intermediate in difficulty processes that led to the building of Earth and of the planets. and risk between lunar and martian missions. . • Some NEOs are carbonaceous. Organic molecules of • As for Mars, robotic and human missions to NEOs provide cometary and/or asteroidal origin played an important role an opportunity for the development of rover, telepresence, in the origin of life on Earth around 4 billion years ago. return-sample and virtual reality space technologies and Comets entering Earth's atmosphere today have their provide a justification for space-station and other means organic molecules largely destroyed or modified thermally. of investigating long-term human survival in space. Like­ Microscopic particles of cometary debris collected in the wise, observations and missions to NEOs are intrinsically stratosphere represent so little cumulative mass that it is international because everyone on Earth is equally at risk very difficult to determine their organic chemistry. The study from the impact ofa large NEO. (The language of the of carbonaceous NEOs may therefore provide important House Science and Space Committee's proposed legisla­ clues to the origin of life. tion for a program like Spaceguard mandates it be done • While many meteorites have been collected on Earth, internationally. ) we are unable to relate these meteorites to the physics, • NEOs represent a new and unknown environment for chemistry and history of any specific solar system asteroids exploration-in many respects, more tantalizing than the or comets. We do not even clearly understand how mete­ partially explored Moon. orites are connected to the different asteroidal and cometary populations. It is possible that a weakly coherent class of Carl Sagan is the David Duncan Professor ofAstronomy NEOs exists that never survived entry into Earth's atmo­ and Space Studies and Director of the Laboratory for 14 sphere and is unknown to us. Planetary Studies at Cornell University. World

lNatch by Louis D. Friedlnan

Paris- The European Space Agency's vision of several launches per year to the and letters to our members. (If you Space Science Advisory Committee has planets. The Mars Surveyor, Discovery would like copies of these materials, rejected the proposed 2003 Intermarsnet and New Millennium programs, plus the you can find them on the World Wide mission plan, which was to have been Pluto Express and the Origins program Web at http://planetary.org/tps/, or you a cooperative ESAINASA venture. In­ (this will search for evidence oflife­ can ask us to send you the information stead, the committee selected COBRAS/ bearing planets in the universe), as well via mail.) Similar statements have been SAMBA, an astronomy mission to as the post- space station development influential in the past during congres­ measure the cosmic background infrared of human flight capability, bode well sional consideration of the NASA bud­ and microwave radiation. for planetary exploration. get. This year, as in the past, letters from The Intermarsnet mission plan had Nevertheless, a dark cloud has the Society and our members have been called for a network of three NASA moved over the horizon, threatening to cited in congressional debate. landers carrying seismometers and obliterate the vision. Both the Clinton We encourage all of you to write to meteorology instruments, as well as administration's proposed budget and Congress and to President Clinton, citing other instruments, to be placed on the Congress' guidelines for 1998 and be­ your support for planetary exploration surface of Mars. The launch vehicle yond imply that space science and and the search for extraterrestrial life. was to have been an Ariane 5, and the planetary exploration will go out of We need to be heard now even more science experiments were to have been business. The accompanying graph than in the past. . European and American. starkly foretells the problem. NASA will now redirect its 2003 The details have been set forth in Louis D. Friedman is the Executive Mars Surveyor mission to be a precursor several Planetary Society statements Director o/The Planetary Society. to a Mars sample return in 2005. ESA's rejection ofIntermarsnet was accompanied by a recommendation NASA Budget for a 2007 planetary mission, which 15~------~ might turn out to be participation in Adnlinistration FV96 Proposed Budget an evolving international Mars sample 14.5+--TL------~:__---r------~ return program. House Appropriations COnlrnittee 14+------~~--~~---r------~ Mainz-At a May meeting of the FV96 Budget as Passed International Mars Exploration Work­ ~ 13.5+--:-:-----:::,....,...---::---~,...----"'.___i~------___l ing Group, Russian space scientists .! described a Phobos and Mars sample & 13+------,~--~~--~~------~ o Senate Budget return mission study. Two concepts o Committee ~ 12.5 were described-one, a launch on the Congressional FY96 large Proton rocket, and the other, a iii Proposed Budget 12+------~~------~~~ Mars-only sample return launched on

the smaller Molniya rocket. The latter 11.5 +------>.oo::--...:.....:-:-----~ . mission could include a solar electric propulsion (SEP) stage now being 11+------>.~-----l developed for a late 1997 test flight from the Mir space station. 10.5 -'---..------.------.------r------.------,-----' The development of this stage is part FY 1995 1996 1997 1998 1999 2000 of a NASA-funded American- Russian initiative for space science from the Various budget plans for NASA (1997 dollars). The budget being considered in calendar year space station. 1996 by Congress is for fiscal 1997 (FY '97), which begins on October 1, 1996. The three lines show the budget passed by Congress last year (FY '96) and the administration's proposals for last year (FY '96) and for this year (FY '97). Dots indicate individual congressional committee Washington. DC- NASA is actions on the FY '97 budget. Projections for fisca/1998-2000 are a/so included. on its way to fulfilling Dan Goldin's Graph; Louis D. Fnec/man, redrawn by B.S. Smith 15 News and

Revievvs by Clark R. Chapman

century ago, scientists were the planets combined. Huge, gaseous scripts/display/short/272/5263/837.html. accustomed to a deliberate Jupiter would be the most representative Your local library may have the complete A pace for research. For years, planet for testing theories of how the issue (a pretty Infrared Telescope Facility even decades, they patiently checked and planets fonned- or so it seemed a quarter picture of Jupiter is on the cover), with rechecked their work before publishing of a century ago. the full articles plus an overview by results in long articles or books. By the Two weeks after probe entry, with Richard Kerr. You could also look at time of Apollo, Viking and Voyager, the some data still dribbling in from Galileo's the illustrated, nontechnical summary at lonely research by individuals had been small antenna, the scientists who had http://ecf. arc .nasa. govI galileo _pro bel replaced by "big science." The world was designed and built the instmments two htmls/Science_summary.html. eager to hear the results, and the media decades ago, and had nursed them through Jupiter, it turns out, is very different became ever more demanding. Scientists the Galileo project's long, turbulent his­ from the target envisioned in the 1970s. were no longer afforded the luxury of tory, were scheduled to tell all at a press Years ago, Voyager and modem ground­ contemplation, but were thrust into live conference at NASA's Ames Research based astronomy had revealed the com­ news conferences while the data had Center. Mercifully, the impasse between plexity of this world-a single probing been on Earth for only a day or two. the president and Congress closed down could hardly represent such a heteroge­ Voyager scientists were uncomfortable the government, including NASA, de­ neous world. And, indeed, as luck would about reporters' demands for instant laying the press conference for a month. have it, the probe penetrated an anoma­ science. Yet when the chief data were Even after a month, the probe scientists lously hot "hole" in Jupiter's cloud deck. pictures, depicting radically new land­ were ill-prepared for the inquisitive press. So the resulting surprises- absence of scapes, it was easy enough for scientists They waited for their 15 minutes of cloud, absence of water, strong' winds­ to describe what was there for all to see. fame, but they had no pictures to show. could reflect an exceptional place, as if an When asked to speculate about why The stream of data was difficult to cali­ Earth probe just happened to land on Mount Ganymede had grooves or why Triton brate, and months and years of analysis Everest, or in Washington, DC. But had geysers, they sometimes offered would be necessary before a responsible comparison of the measurements of the theories, though those theories rarely report could be written. Yet the world various instruments is beginning to sug­ survived more intensive research. Still, wouldn't wait. So, in January, the scien­ gest that Jupiter may be quite different it worked OK. The press and the public tists sat on a stage, offered no results, but from what most of the experts had thought. were satisfied by neat new pictures and invited reporters to ask questions anyway. Watch the story develop on the Web. accompanying sound bites, and the Used to being fed an announcement to The Web provides the instant gratification longer-tenn purposes of science were serve as a foil for their questions, the of our ever more impatient, fast-paced satisfied by post-mission data analysis journalists were dumbfounded. An hour culture. However, the postings will be programs, through which NASA funds later, the press conference was over, but continually updated as the research ma­ mission and non-mission scientists to the world had learned virtually nothing tures-if NASA provides the funds to figure out what all the data really mean. about Jupiter. One reason was that the the scientists to ensure that the careful Last December, Galileo's probe blasted scientists had not yet learned much about scientific work is done over the next (at more than 100,000 miles per hour) Jupiter. But the media had a few sound years. It used to be that instant science­ into Jupiter's atmosphere in one of the bites, and the evening news shows treated the press-release pictures and accounts premier technological accomplishments Galileo's achievement with due respect. from the early press conferences- was of NASA's planetary exploration program. The pressure to produce continues all that penetrated the public's conscious­ Parachuting a collection of high-tech unabated, and the ensuing months have ness. Now there is an instant medium instmments, the probe radioed back an begun to reveal some results about Jupiter that, if managed properly, may provide hour's worth of meteorological observa­ that may stand the test of time. The most public awareness of the continually tions and samplings of the giant planet's pressing requirement for the probe team evolving research. atmosphere to a depth of 100 miles. The was to write articles for a special section mission was conceived in the 1970s to in the May 10th issue of Science maga­ Clark R. Chapman, as a member of the literally take the temperature and sample zine. Brief summaries of these articles can Galileo imaging team, will be stl1dying the composition of the body that con­ be found at a Web site with a long URL: images to be taken by the orbiter's 16 tains over 70 percent of the mass of all http:// science-mag. aaas. orgl sciencel camera until the end of 1997. Society NelNs

Celebrate Viking's more about either ofthese tours, contact Council of Scientific Unions) conference 20th Anniversary me at Society headquarters. - CJ at the University of Birmingham July 14 On July 18 and 19, 1996, at the National to 20. We'll have a display at the con­ Academy of Sciences in Washington, Open House at ISAS ference, as well as a Red Rover, Red DC, there will be a celebration of the The Institute of Space and Astronautical Rover demonstration at the Birmingham 20th anniversary of the Viking mission Science (ISAS) in Japan will host its Museum of Science. to Mars. This tribute to Viking, cospon­ annual open house on Saturday, August Society Executive Director Louis sored by The Planetary Society and 3, 1996. And we' ll be there, with Friedman will host an evening event on NASA, will include evening lectures Planetary Society exhibits featuring July 20 in Birmingham; on September 21 , by Carl Sagan and NASA Administrator such special projects as Red Rover, he will speak at one of many Society · Daniel Goldin and an all-day symposium Red Rover and Visions of Mars. events celebrating National Astronomy on Mars exploration. For details, please Phone 0427-51-3911 , extension 2204, Week. For information, contact me via contact me by phone at 818-793-5100; for information; the address for ISAS e-mail ([email protected]) or bye-mail. [email protected]. is 3 -1-1 Y oshinodai, Sagamihara, telephone (0121-356-5446). -Susan Lendroth, Manager ofEvents Kanagawa. -SL -Andy Lound, Regional Coordinator and Communications Share Your Photos Ride 'ern, Rover Mars Madness Did you capture a photograph of comet Rovers from around the world will be Do you want to be there in person as Hyakutake that you are especially showcased at the February 1, 1997, the powerful Proton rocket rises from proud of? Do you want to share it? The Rover Roundup on the beach in Santa its launchpad this November 16, send­ Planetary Society would like to collect Monica, California. This event is spon­ ing Mars '96 on its long-awaited trek to some striking portraits of the comet for sored by The Planetary Society in cOQP­ the Red Planet? Then come with us to possible use in future publications or eration with NASA and several other Russia and the Baikonur Cosmodrome videos. If you want to participate, space agencies. A three-day international in Kazakhstan. Or would you like to please send your work to me at Society conference on mobile planetary robots be at Cape Canaveral as Mars Global headquarters. We prefer prints or slides will precede the public event. Surveyor begins its adventure? Our tour over digital formats, unless you have If you are interested in the technical to Orlando, Florida, and the Kennedy a large, high-resolution image. conference Call for Papers, contact Space Center (November 2 to 9) will - Donna Stevens, Assistant Editor India Wadkins at Society headquarters. take you there. For information, call me Details of the public event will be at Society headquarters or send e-mail Countdo1Nn With Galileo available later. -SL to [email protected]. Don't miss this The Society is counting down to Planet­ chance to witness our return to Mars. fest '97 with a series of events tied to - Cindy Jalife, Manager of GaWeo's encounters with the moons More Ne1Ns of Jupiter. Here's a preliminary list: Program Development The Mars Underground News: • July 25, 1996, Pasadena, California United States presidential candi­ For Cornet Watchers • October 26, 1996, Tucson, Arizona dates and space ... the P1anet-B We have two new tours in the works, • December 4, 1996, Providence, mission .. .images of Mars. and they're both focused on the 1997 Rhode Island The Bioastronomy News: arrival of comet Hale-Bopp. Both trips • January 22, 1997, Honolulu, Hawaii Preparing for an extraterrestrial will take place March 22 to 29, when • March 1997, Davenport, Iowa signal. .. how to respond to signals ... the comet is expected to be at its most If you live in the area of a scheduled the ongoing search for spectacular. One trip will take us to event, you'll be notified by mail. You extraterrestrials. Hawaii, where we'll comet-watch with may also contact us for details on any The NEG News: planetary scientist Steven Edberg of the event of special interest to you. -SL Spacewatch ...more Hyakutake Jet Propulsion Laboratory by night and news ... discoveries of new objects. explore the islands by day. The second Feast of Events For more information on these is tentatively scheduled for Fairbanks, in Great Britain newsletters, please contact Alaska. We'll have the special pleasure The Planetary Society will be participat­ Planetary Society headquarters; of viewing the comet with Alan Hale, ing in the 1996 COSPAR (Committee seepage 2. its codiscoverer. If you want to know on Space Research of the International 17 /

Basics 0" Space.,light: l

by Darve Doody

n the previous installment, we looked at propulsive choices to meet the long-term demands of interplanetary power, which is provided to a spacecraft by its chem­ spacecraft: photovoltaics and radioisotope thermoelectric J ical-burning launch vehicle, augmented by onboard generators (RTGs). propulsion systems. (See the MarchiApril1996 Planetary Report.) But interplanetary spacecraft also need electrical Rhotov...u'f:ai.cs power to operate valves, computers, radio transmitters and As the name suggests, photovoltaic materials have the receivers, data storage devices and a host of sensors and wonderful, seemingly magic ability to convert light to instruments. How does a spacecraft meet these electrical electricity. You might have a desktop calculator that runs power needs? on ambient light by using a photovoltaic cell. Crystalline silicon and crystalline gallium arsenide are two typical ~olt"~De atrtil (C.u-.rr.:enr: choices of photo voltaic materials for deep space applica­ First, let's describe two basic measurements of electrical tions. Gallium arsenide crystals are grown especially for power: voltage and current. We can compare electrical photovoltaic use; but silicon crystals are mass-produced voltage with water pressure. The 12 volts (V) in your auto­ for the microelectronics industry and are less expensive. mobile is a relatively low electrical pressure. Low water Gallium arsenide is notably tougher and more efficient. pressure could be used in, say, a drinking fountain. The Crystalline ingots of either material are sliced into wafer­ l20-volt service in United States homes provides a higher thin circles, and then some metal is deposited onto each electrical pressure. If you were to increase the pressure in surface: a thin grid on the Sun-facing side, a flat sheet on the your drinking fountain tenfold, the water might squirt back. Connect one wire to each metal surface, and you have across the room when you went to take a s.ip (our office an electrical power source-a photovoltaic cell. When the used to have one that did nearly that). cell is exposed to direct sunlight at Earth's distance from The other electrical measurement, current, is analogous the Sun (1 astronomical unit, or AU, which is equivalent to to the water's flow rate. The small pipes in your drinking 150 million kilometers or 93 million miles), a current of fountain carry a small current of water- only a few liters about 1 ampere, at a quarter of a volt, can be produced by or so per minute. Large pipes supplying a fire hydrant can a typical 6-centimeter-diameter (2A-inch) silicon cell. carry a substantially higher current, perhaps thousands of (Operating closer to the Sun creates more power.) liters per minute. These cells are trimmed into appropriate shapes and You could vary the flow rate somewhat in your drinking sizes and cemented onto a substrate. Electrical connections fountain by changing the pressure, and this is true in electri­ are then made among all the cells to provide an output cal circuits as well: Increase the voltage supplied to a light­ suitable to power a spacecraft. These assemblies are called bulb, and more current will flow through it. But only until solar arrays. In flight, the cells absorb sunligh~ and get it breaks. You wouldn't trust drinking-fountain-sized pipes quite warm, so a solar array's cement and substrate have to fight a fire. And guess what? It takes larger-diameter to be thermally conductive to help dissipate the heat. electrical wires to safely carry a larger electrical current. Photovoltaics are only practical for spacecraft operating Electrical current is measured in amperes (A). The 12- relatively close to the Sun. Magellan used solar arrays, as volt fan in your automobile might consume half an ampere will Mars Global Surveyor. TopexiPoseidon, the Hubble at its low setting, and 2 amperes on high. Volts multiplied Space Telescope and most other Earth-orbiters also use solar by amperes gives a convenient single measure of power: arrays. Generally, solar arrays for interplanetary spacecraft watts, abbreviated W. are designed to be movable appendages, and the spacecraft's Roughly 300 to 1,500 watts (1.5 kilowatts, kW) ofelectri­ computers keep them pointed toward the Sun. Prolonged cal power was required by the systems aboard spacecraft like exposure to sunlight causes photovoltaics' performance to Magellan, which mapped Venus; Galileo, now exploring degrade in the neighborhood of a percent or two per year; Jupiter; Cassini, the Saturn spacecraft; or the Voyagers, trav­ this degradation happens more rapidly if the cells are eling in the outer solar system. But what power source can exposed to gas, dust or particle radiation from solar flares. supply a spacecraft for years, or even decades? Batteries just Spacecraft that have solar arrays are usually equipped won't last that long, notwithstanding the pink bunny adver­ with rechargeable batteries. The batteries are recharged tisements seen so frequently on US television. Batteries did whenever the solar arrays are in sunlight. But when the arrays power Galileo's atmospheric probe, but it only had to run its are shadowed by the planet, or when they are pointed away instruments and transmitter for a little more than an hour­ from the Sun during spacecraft maneuvers, the batteries 18 an appropriate task for batteries. There are two realistic take over, discharging to power the spacecraft until the Simplified Sun returns to the arrays. Nickel- cadmium (NiCad) batteries, not unlike the, ones in a Spacecraft Electrical System portable electric shaver (but larger), are fre­ quently used in spacecraft. After hundreds of charge-discharge cycles, NiCad batteries degrade in performance, but they may be RADIANT HEAT rejuvenated by carefully controlled deep ~ discharge and recharge cycles, an activity SOLAR ARRAV 1 ~ SPACECRAFT called battery reconditioning. SYSTEMS

Beyond the orbit of Mars, the Sun's light is REGULATOR -~ too weak to be practical for generating power ~ -~ SWITCHES CONTROLLED ~ with solar arrays. Craft bound for Jupiter and BY THE SPACECRAFT'S + BATIERV the planets beyond carry their own sources of COMMAND COMPUTER power: radioisotope thermoelectric generators. RTGs contain pellets of plutonium 238 in the form of an oxide pressed into ceramic pellets. SOLAR ARRAV 2 As the radioactive plutonium decays, it pro- Convert to Adiustto Store for periods Distribute to duces heat, and this is converted into electricity electricity constant voltage of shade spacecraft systems by an array of thermocouples made of silicon- germanium junctions. Any waste heat is radiated into space by an array of metal fins. Chart by Dave Doody; redrawn by B.S. Smith The very name plutonium conjures images of extreme hazard, and the possibility, although extremely remote, of an accident releasing this element into Earth' s atmosphere has not been ignored by It's important for a spacecraft's computers, instruments, spacecraft engineers. In the US space program, RTGs are and other components to have a precise, constant voltage. designed to survive launch accidents without releasing the To do this, the electrical power source is typically designed plutonium, and these designs have been tested by the US to produce a slightly higher voltage than needed, and this Department of Energy. In fact, the prelaunch procedures for supply is fed to a regulator. The regulator converts the excess RTG-carrying spacecraft are so rigorous that the office of electrical energy into heat, most of which is radiated away the president of the United States must be satisfied of their into space via a radiating plate, and a controlled voltage is safety and approve each launch. supplied to the main bus. Magellan, working at Venus' RTGs must be located on the spacecraft in such a way as distance from the Sun, had to be operated very carefully to to minimize their impact on particle-detecting and infrared­ be sure all its components were kept within the right tempera­ detecting science instruments. Galileo' s RTGs are mounted ture ranges. Once in a while, it was convenient to point its behind reflective shields to shade the near-infrared mapping solar arrays slightly off from the Sun so they would produce spectrometer from the heat they radiate, Much of the space­ slightly less electrical power, thus causing the regulator to craft's mass shields Galileo's high-energy particle detector produce a bit less heat! from the RTGs' gamma radiation. RTG performance Typically, spacecraft power supplies are designed to pro­ degrades in flight just slightly faster than what is normally vide about 28 volts DC (direct current). With DC, the polari­ expected for photovoltaic sources, except that RTGs are ty, or direction of current flow, is constant. Some instruments much more rugged and therefore more reliable under harsh or components, however, may require higher or lower volt­ conditions. ages, or they may require alternating current (AC; here the direction of current flow reverses, perhaps 400 times per iR~9uJa.iD;9 lEJ:e:cf:Mi~di~y second). These special needs are met by small, efficient power ii:n ~lXaCJe converters, which take in the normal spacecraft electrical Virtually every electrical or electronic component on a space­ supply and provide the required output. You may have used craft may be switched on or off via commands sent from a similar kind of power converter in an airplane if you plugged Earth (see the Basics of Spaceflight colunm in the November/ your shaver into an outlet in the lavatory. December 1995 Planetary Report). This is accomplished In the next issue, we'll look at how interplanetary space­ using solid-state or mechanical relays that connect or discon­ craft deal with the effects of extremely hot and cold temper­ nect the component from a common distribution circuit, atures in their environment. frequently called a main bus. On most interplanetary space­ craft, you have to power off some components before you Dave Doody is a member 0/ the Jet Propulsion Laboratory 's can switch others on, in order to keep the electrical load with­ Advanced Mission Operations Section and is currently work­ in the limits of the supply. Voltage and current are measured ing on the Cassini mission to Saturn. and telemetered from the main bus and other points in the electrical system, including many if not all spacecraft compo­ If you have access to the World Wide Web (via a Web nents and instruments. This information is very helpful in browser like Netscape or Mosaic), be sure to look in on making sure systems and instruments are working properly, JPL's Basics a/Space Flight manual, on-line at as well as in troubleshooting when problems arise. http://www .jpl.nasa.gov/basics/. 19 ,------

Questions and Ansvvers

If the Search for Extraterrestrial In­ has many transmitters using thousands SET! will probably only observe our telligence (SETI) was based on Mars to millions of watts. These should be most powerful transmissions, such as (or Alpha Centauri) and aimed at easy for Martians to detect. For exam­ the television and military radar of the Earth, would it detect any of the signals ple, the giant Arecibo radio telescope United States and Russia. Beyond the that it is now searchingfor? Ifso, in Puerto Rico has a million-watt radar nearest stars, the distances are so great which types ofintelligent signals transmitter. It's used to bounce radio that the transmissions get buried in cos­ would it select for further scrutiny? signals off planets, moons, comets and mic noise. However, a signal beamed -Tom and Joe Parkinson, asteroids. It's so powerful that it could at its target could be detectable much Toronto, Canada detect a steel golf ball on the Moon. farther away: A civilization no more They'd be able to learn something advanced than ours could build a trans­ If there were Martians and they had a about our civilization. They'd discover mitter that we could detect anywhere in SET! program, they would have no that our planet rotates every 24 hours, the galaxy. difficulty detecting Earth's radio and and that there are great concentrations If they are more advanced, it's even television transmissions. Human SETI oftransmitters in certain regions. They possible that they might be able to de­ projects are able to pick up the feeble would even deduce something about tect our most powerful television and transmissions, from beyond Pluto, of politics when they found over a hun­ radar signals even though these are not the Pioneer spacecraft, whose transmit­ dred languages, with most confined to beamed at them. One trick would be to ter uses a few watts of power, similar to particular areas. use their star as a gravitational lens. If what a refrigerator lightbulb uses. Earth If there are Alpha Centaurians, their they put a receiver at the right location,

Factinos

ather than finding some new satur­ satellites (see image below). November/December 1995 issue of The R nian moons, as some researchers Last year, Amanda S. Bosh of Lowell Planetary Report). But after further study­ originally reported, the Hubble Space Observatory in Flagstaff and Andrew S. ing the data, Bosh has now determined Telescope (HST) may have instead seen Rivkin of the University of Arizona an­ that only one of the bodies is a new moon. clouds of ice and dust orbiting the ringed nounced that during the May 22 ring-plane The other, named S3, has an orbit so simi­ planet. Some of that debris, however, crossing, the HST detected two new lar to Saturn's F ring that it represents a may be the shattered remains of tiny objects that appeared to be moons (see the small clump of material from the ring. In' HST images captured during the These false-color images show August 10, 1995, ring­ Saturn's inner moons, Pandora, Janus, Rhea, Mimas and Tethys, plane crossing, Philip as seen by the European Southern ·D. Nicholson of Cor­ Observatory's 3.6-meter (140- nell University and inch) telescope in La Silla, Chile. The upper panels show the west­ his colleagues detect­ ern edge of Saturn's ring plane. ed two never-before­ · The lower panels reveal the · newly discovered body 56, seen bodies, as well which is believed to be a clump as S3. The team has · of debris, not a new moon. In the concluded that none April26, 1996, issue of Science, Philip O. Nicholson and his col­ are moons. The objects leagues mentioned that 53 and must have been creat­ 56 could well be the same clump ed during the last 14 in Saturn's F ring. Image: European Southern Observatory years, because they are too big and bright for the Voyagers to have overlooked dur-. 20 ing their flybys of the ------_.. _------

where our radio signals are focused offset the adverse effects of micro­ by gravity, they might be able to gravity on bones, muscles, the car­ eavesdrop on some of our routine diovascular system, the nervous transmissions even thousands of system and other body systems. light-years away. Research aboard the space station - TOM McDONOUGH, will also teach us much about how SET! Coordinator these systems work on Earth. One of the key research compo­ We often read that prolonged ex­ nents of the international space posure to weightlessness is damag­ station will be a large centrifuge ing to humans, and yet we know· (but not large enough for humans) that there are plans to put people that will allow us to study how in orbit on the space station and different levels of gravity affect perhaps on aflight to Mars. Why living organisms. This may lead to do we no longer hear olthe torus­ the development of space stations shaped space station or vehicle and other vehicles that create arti­ team of US and German astrophysicists that creates gravity by rotating? ficial gravity by rotation like the A has made the first ever detection of X -L.S. Kypta, torus-shaped space station you de­ rays coming from a comet. Their discovery of a Milpitas, California scribe. But before the development strong radiation signal was made on March 27, of these spacecraft, we will have 1996, during observations of comet Hyakutake As we gain experience in the joint to become better at identifying the using Germany's orbiting ROSAT satellite. USlRussian shuttlelMir program requirements for, and effectiveness Scientists had optimistically predicted an X-ray and begin constructing the interna­ of, other "simpler" measures to intensity that turned out to be 100 times tional space station, we are learn­ combat the effects of micro gravity. weaker than what ROSAT detected. Strong ing more about the effects of pro­ We should also have a better under­ changes in the brightness of the X rays were longed exposure to microgravity standing of the level of artificial another surprise. These changes, typically a (weightlessness) on human beings. gravity necessary to offset these few hours apart, were visible from one ROSAT Our experience on these space effects. image to another. stations will allow us to continue - EARL W. FERGUSEN, Image: C. Lisse, M. Mumma, NASA Goddard Space Flight Center; K. oennerl, to develop and refine measures to NASA Headquarters J. Schmitt and J. Englehauser, Max Planck Institute for Extraterrestrial Physics

planet in the early 1980s, says Nicholson. Davis, Texas, in November 1993. Moon, to a height of about 14,000 kilo­ Also, the brightest of the three bodies is During the eclipse, the Moon was in meters (9,000 miles) above the surface. elongated, unlike a satellite. Earth's shadow, and the normally bright, This is almost twice the size of the lunar Nicholson noted that all three bodies scattered moonlight was absent. This re­ atmosphere that the Boston team recorded seemed to have disappeared by November vealed a faint glow from sodium gas high in earlier observations when the Moon 21, 1995, when the HST viewed Saturn in the lunar atmosphere. The scientists was at quarter phase (see the March/April again. Bruno Sicardy, a scientist from the were surprised to find that this glow ex­ 1995 issue of The Planetary Report). Paris Observatory in Meudon, France, tends over nine times the radius of the -from Boston University . suggests that the objects, believed to lie near the F ring, disappeared precisely be­ RAYLEIGHS cause oftheir location. Here Saturn's tidal 1000 This image depicts a color­ coded representation of the pull could break off a piece of a small Moon's sodium atmosphere, moon. This loose package of material which was observed during would briefly form a cloud of debris the total lunar eclipse of November 29, 1993. The bright enough to be seen by a telescope. brightest Signals, showing -from R. Cowen in Science News the highest quantities of 100 sodium, are magenta and red, while the faintest Signals are he first detailed picture ofthe Moon's depicted as blue. The full T extensive atmosphere (see image at Moon's position is indicated right) was released by researchers from behind the occulting mask in the telescope. The umbra Boston University. In the October 5, 1995, (Earth's full shadow) and issue of Nature, Michael Mendillo and penumbra (partial shadow) Jeffrey Baumgardner described their ob­ 10 are also shown. Image: M. Mendillo and servations of the full Moon during the J. Baumgardner, Boston University one-hour totality phase of a lunar eclipse at the McDonald Observatory in Fort 21 II JPu!Ae aAe fJ1o.neeA w.uf4 fAal ~ tAeiJL ~ WPu!Ae ~ neu.e/l, 1U1J'L"

-YJrun W~ 9-oU, ~J 1858-1911

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Oon Davis created th is "digital intermediate version" of a painting in progress on his Maci ntos h by first sca nn ing a small black-and -white airbrushed piece and then coloring and refining the image in the computer, Don is currently producing an im ation and still images for the upcoming British TV show The New Solar System, as we ll as concept art and special effects sequences for various clients,

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