The Volume XVII 01) the Cover: "Fantastically weird" slipped out as geologist Jim Head Table of Number 2 described the latest Galileo images of Euro~a. Thi ~ is one March/April1997 of the most enigmatic worlds yet seen by spacecraft, and Contents the closer we look, the stranger it gets. It may possess an ocean beneath a water-ice crust, perhaps hiding a potential habitat for life. Here we show the moon as it appeared from 677,000 ki lometers (420,000 miles) away last September during Galileo's flyby of Gany mede. At left is a false-color Features image, with contrasts enhanced to bring out compositional Waltzing by Mathilde: differences in the primarily ice crust. At right is a natural­ 4 NEAR's First Asteroid Encounter color image, showing Europa as it might appear to an Asteroids aren't the most glamorous objects in the solar system, but they contain crucial observer riding the spacecraft. Images: JPUNASA clues to the origin and evolution of our planetary family. Plus, those that pass through Earth 's neighborhood pose a distinct threat to the future evolution of some life-forms on this planet. On its way to explore the tiny world Eros, the Near-Earth Asteroid Rendezvous spacecraft is preparing to encounter another small object with great potential, Mathilde. Froln 9 Farevvell, Pioneer The The Voyagers' flights through the outer solar system may have been more thrilling, and the CaWeo mission to the Jupiter system will produce more data, but both these missions Editor depended for their success on the first spacecraft to blaze a trail to the outer solar system: Pioneer 10. That hardy little craft, still operating after 25 years, will soon fall silent­ a victim of budget cuts, not the rigors of space. he theme has pervaded the space Tprogram since its birth, some­ 10 Weird and Wonderful: times playing softly in the background, Europa Keeps Her Secrets other times forcefully dominating So far we have conclusive evidence of a global ocean on only one world-Earth. But missions and programs. That theme is, Jupiter's moon Europa has tantalized scientists with hints that it, too, may possess large of course, life in the universe. With bodies of liquid water, even if they are hidden beneath an icy shroud. Calileo has sent us CaWeo circling closer and closer to the best images yet of this weird little world, but as yet there is no way to know for certain Europa, spll,cecraft flying to Mars, and if there is a Europan ocean. powerful telescopes finding more and Sagan's Fire: more planets around other stars, the 14 A Nevv Challenge theme is once again g~ining power. The Planetary Society faces a future filled with challenge and opportunity. Bruce Murray, NASA has committed to extending Acting President, and Louis D. Friedman, Executive Director, ask your help in guiding the CaWeo's funding to cover the Europa Society to the best of all possible futures. Extended Mission, in the hopes of determining if an ocean lies beneath its icy surface. Both NASA and the Departlnents National Science Foundation are encouraging research to determine if 3 Men1lbers' Dialogue the meteorite ALH84001 does hold traces of ancient Martian life. Returning 15 World Watch a sample of Mars to Earth has gained priority in NASA's plans for the next 16 Basics of Spaceflight century. And questions concerning 18 Nevvs and Revievvs extrasolar planets have shifted from "Do they exist?" to "Which ones 1 9 Society Nevvs might support life?" This is a time of fantastic opportu­ 20 Questions and Ansvvers nity for the Planetary Society to reach an increasingly receptive audience with our message. The only way to find life on other worlds is to explore Contact Us them. It's our job to make that happen. --Charlene M. Anderson Mailing Addres s: The Plan etary SOC iety, 65 North Catalina Aven ue, Pasadena, CA 91106-2301 General Calls: 818-793-5100 Sales Calls Only: 818-793-1675 E-mail: tps @mars .planetary.org World Wide Web Home Page : http ://p lanetary.org /tps/

The Planetary Report (ISSN 0736-3680) is published bimonthly al the editorial oHices of the Planetary Society, 65 North Catalina Avenue, Pasadena, CA 91106-2301,818-793-5100. II is available to members of the Planetary Society. Annual dues in the US are $25 (US dollars); in Canada, $35 (Canadian dollars). Dues in other countries are $45 (US dollars). Printed in USA. Third-class postage at Pasadena, California, and at an additional mailing office. Canada Post Agreement Number 87424 A ...... '" , Editor, CHARLENE M. ANDERSON Technical Editor, JAMES D. BURKE ~ Assistant Editor, DONNA ESCANDON STEVENS Copy Editor, KARL STULL THE-PL.A~TfRV SOCIETY Production Editor, WILLIAM MCGOVERN Art Director, BARBARA S. SMITH Editorial Assistant, JENNIFER VAUGHN o .~ -e- ¢ -e- 0 ViewPoints expre ssed in columns or editorials are those of the authors and do not necessarily represent pOSitions of the Planetary Society, • its officers, or advisors. © 1997 by the Planetary Society. o .------IF-======~~~--~~~---======······==~----·------·----

Co-f'ounder CARL SAGAN Members' 1934· 1996 Board of Directors

BRUCE MURRAY Dialogue Vice Presi dent Professor of Planetary Science, california Institute of Technology

LOUIS D. FRIEOMAN Executive Director

NORMAN R. AUGUSTI NE PreSident, Lockheed Martin Corporation

JOSEPH RYAN Executive Vice President and General Counsel, Marriott International

STEVEN SPIELBERG director and producer

LAUREL L WILKENING Chancelfor, University of California, Irvine

Another option? a desire to be rid of the endless tion award to Project BETA (see Board of Advisors Soon after hearing about the government bureaucracies the November/December 1996 DIANE ACKERMAN demise ofthe Mars '96 mission involved in space exploration. Members' Dialogue) is a remind­ poet and author BUZZ AL DR IN I realized that the microdot But I believe that privatization er to us all of the best humanity Apu lia 11 astronaut RICHARD BERENOZEN with Planetary Society members' will replace the endless govern­ has to offer and why, eventually, educator and astrophysicist

names was lost too, and I was ment problems with endless we may be worthy representatives JACQUES BLAMONT Chief Scientist, Centre National saddened even further. I urge business problems. of our planet in whatever commu­ d'Etudes Spatia/es, France the Society to approach NASA I think government involve­ nity the universe has to offer. RAY BRADBURY poet and author with a proposal to refly the lost ment at this time is good. This --EVAN MALONE, ARTH UR C. CLARKE microdot and the Visions of allows the motives to be set Philadelphia, Pennsylvania author CORNELIS DE JAGER Mars CD-ROM on the 1998 more by people than by profit. Professor of Space Research, The Aslronomicallnstitute at Utrecht, Mars Surveyor lander mission. A private company is under no Praise the Netherlands The opportunity to have one's obligation to listen to voters. It Thank you for existing-for FRANK DRAKE Professor of Astronomy and Astrophysics, name fly to the Red Planet on a would pay more heed to markets remaining a strong voice, always University of California, Santa Cruz JOHN GARDNER robotic explorer is a very roman­ and backers. A government-sup­ informing and enlightening the founder, Common Cause

tic notion indeed. I hope that you ported J1rivate company could public about the many wonders MARC GARN EAU will soon be approaching NASA turn its attention from survival of our solar system and beyond. Canadian astronaut GEORG IY GDLlTSYN to suggest the inclusion of these and business to what people in I appreciate the fact that the Institute of Atmospheric Physics, Russian Academy of Sciences important "payloads." general are interested in doing. Society has spoken to those in THEODORE M, HESBURGH President Emeritus, --JOEL W POWELL, But such a company is no longer our government to ensure that University of Notre Dame

Calgary, Alberta, Canada free from government or private they are made aware of the great SHIRLEY M. HUFSTEDLER bureaucracies. importance of such experiments educator and jurist GARRY E. HUNT It is too late and probably tech­ Things should stay as they as the Mars Balloon. I thank your space SCientist, United Kingdom nically impossible to put Visions are until it's more reasonable for organization, Louis Friedman, SERG EI KAPITSA fnstitute for Physical Problems, of Mars on the 1998 Mars private citizens to undertake and Carl Sagan for your contin­ Russian Academy of Sciences GEN. DONALD J. KUTYN A (RET.) Surveyor lander. That mission businesses involved with being ued hard work and for sharing it former Commander, US Space Command has very tight weight and volume m space. with those who are interested. JOHN M, LOGSDON Director, Space Policy Institute, constraints. The CD also con­ -PAUL RICHMAN, - SHAWNA MERLIN George Washington University tains material particular to Mars Vancouver, British Columbia, BURCH, Boise, Idaho HANS MARK The University of Texas at Austin

'96 and should be changed to fly Canada JAMES MICHENER on another mission. The small NASA's Budget author MARVIN MI NSKY stations, on which were mounted Inspiration Regarding the issue of spending Toshiba Professor of Media Ans and SCiences, the CD and the special Society Although I am frequently struck NASA's money on social pro­ Massachusetts Institute of Technology label with the radiation recorder with awe by the photographs jects rather than on space explo­ PHILIP MORRISON Institute Professor, and our members' names, is being presented in your magazine and ration, consider this: if Queen Massachusetts Insti(ute of Technology PAUL NEWMAN considered for flight in 2001 as often moved by the wonderful Isabella had taken the money actor part of "Mars Together." We will example of cooperative effort she gave Christopher Columbus JUN NISHI MURA former Director General, certainly discuss this with NASA between the public and profes­ and invested it in social projects Institute of Space and Astronautical SCience, Japan sionals (and even policy-makers) and the Russian Space Agency instead, just imagine the utopia SALLY RIOE Professor of Physics, as an idea for Mars landers in that the Planetary Society repre­ Spain would be today. University of California, San Diego, 2001 or later. sents, I often feel despair at -E. R. LEIBFRITZ, and former astronaut ROALO Z. SAGOEEV --Louis D. Friedman, humanity's inability to fix goals San Jose, California former Director, fnstitute for Space Research, Executive Director that extend beyond our own Russian Academy of Sciences Please send your letters to HARRISON H. SCHMID lives, beyond our personal gain. former US Senator, New Mexico, Don't privatize But in my frustration-darkened Members' Dialogue, and Apollo 17 astronaut S. ROSS TAYLOR I disagree with Donald Brewer's sky, there is sometimes a reentry The Planetary SOCiety, Professorial Fellow, optimism concerning the privati­ vehicle of inspiration. 65 North Catalina Ave. , Australian National University, Canberra JAMES VAN ALLEN zation of space agencies. (See The gesture made by Jane Pasadena, CA 911 06~2301 Professor of Physics, University of Iowa the November/December 1996 Rigby in donating a portion of or e~mail Planetary Report.) He expresses her Geraldine R. Dodge Founda- tps,des@ mars . pl ~ etary.org 3 Dimensions: .. 50 x 50 x 70 kilometers 30 x 30 x 40 miles Class: ...... C (Carbon Rich) Rotation Period: ...... 17.4 days (9,.6a.. Perihelion: ...... 1.94 AU Aphelion: ...... 3.35 AU Inclination: ...... 6.7 degrees Orbital Period: ...... 4.31 years ------~~~~~~~~==~~~~

L..J 951 Gaspra (Gali/eo) JOKM 253 Mathilde (NEAR) 6 MILES

Top left: On August 28, 1993, Galileo passed by Ida, an irregularly shaped asteroid in the main belt between the orbits of Mars and Jupiter. Mathilde is much larger than either of the asteroids visited by Galileo. Left: Gaspra was the first asteroid to be scrutinized close up by a spacecraft-and thus by the humans looking through the spacecraft's cameras. Galileo flew by Gaspra on October 29, 1991 on its way to the Jupiter system. Images: JPUNASA; Illustration: Peter Thomas

ate in 1994, only one year before the launch ofthe wife of astronomer Moritz Loewy, then the vice director of Near-Earth Asteroid Rendezvous (NEAR) spacecraft, the Paris Observatory. Although the asteroid's existence Lthere was a bit oftunnoil within the flight project. has been known since 1885, it was only following the Mission designers had discovered that the trajectory to announcement of NEAR's possible flyby that astronomers asteroid Eros would take the spacecraft closely by a large made extensive physical observations using telescopes on asteroid named Mathilde. Should we make plans to have Earth. These showed that far from being a garden-variety NEAR observe this large asteroid? To do so would use up asteroid, Mathilde is an extremely unusual object. precious fuel and further complicate an already complex To date, the only spacecraft encounters with asteroids mission plan. Risks would increase because the spacecraft have been the CaWeo flybys of95l Gaspra in October 1991 was custom-made to orbit asteroid Eros, not fly by Mathilde, and 243 Ida in August 1993. Both objects are S-type asteroids, and the spacecraft's observations might require more power the most common asteroid type in the inner part of the than its solar panels could provide. asteroid belt (the region between the orbits of Mars and Even worse, dust particles orbiting Mathilde might destroy Jupiter, littered with rocky bodies too small to be considered the spacecraft as it flew past at 10 kilometers per second-­ planets). Asteroid 433 Eros, NEAR's destination, is also an . ten times faster than a rifle shot. S-type asteroid. However, the most common type of asteroid Some argued that the risks were too high and the prudent in the outer asteroid belt, comprising the dark and primitive thing to do was to ignore the potential June 1997 flyby of C-type objects, has yet to be investigated by spacecraft. Mathilde. After all, the NEAR spacecraft would spend nearly Spectral observations by Richard Binzel and his colleagues a year in orbit around the asteroid Eros, and the CaWeo show that Mathilde is a C-type asteroid--and a big one at spacecraft had already studied two asteroids, Gaspra and that. Its spectrum falls between those of the two largest as­ Ida. Was it worth the risks to fly closely past yet another teroids known, 1 Ceres and 2 Pallas. Mathilde is twice the asteroid? Was Mathilde so out ofthe ordinary that well size of Ida and four times the size of Gaspra. And because it developed mission plans should be changed? Could we make reflects only 4 percent of the light falling upon it, Mathilde discoveries during this asteroid flyby that hadn't already is one of the blackest objects in the solar system. been made during the Gaspra and Ida flybys? The answers Mathilde' s slow spin is another intriguing characteristic. turned out to be yes, yes, and yes. Using a series of observations from the first half of 1995, Stefano Mottola and his colleagues determined that its Asteroid 253 Mathilde rotation period is an extremely long 17.4 days. Only two Asteroid 253 Mathilde was discovered on November 12, asteroids, 288 Glauke and 1220 Clocus, have longer periods 1885 by Johann Palisa in Vienna, Austria. The asteroid (48 and 31 days, respectively), and there is no obvious mech­ name was suggested by V. A. Lebeuf, the staff member of anism to account for these extremely long asteroid "days." the Paris Observatory who first computed an orbit for the Collisions by neighboring asteroids could be enough to slow new asteroid. The name Mathilde is thought to honor the an asteroid's spin, but statistically it is very unlikely that a 5 ~B/~: NEAR Spac.ecraft Summary 97hl!/ ~ W-w:!Jd ••mum "rh.' s.~r panels n February 17, 1996, a Delta 2 rocket launched Othe Near-Earth Asteroid Rendezvous (NEAR) spacecraft toward its encounters with two very 1.S-meter antenna different asteroids. NEAR is the first mission in NASA's Discovery program for "faster, cheaper, better" planetary exploration. Simplicity and low .. cost were the main considerations in the design of the NEAR spacecraft. The science instruments, solar panels, and the high-gain antenna are mount- ed to the body of the spacecraft rather than on a movable platform. Although this configuration Thruster ------~ increases the complexity of spacecraft operations, it was an important factor in overall cost contain- ment. NEAR's development cost totaled less than ~idI._I!Ii!J:;'I-___ Instruments $125 million in real-year dollars-well under the Discovery cost cap of$150 million in Fiscal Year 1992 dollars. Science Payload: Total Weight: 800 kilograms The primary objective of the NEAR mission is • Multispectral imager 1800 pounds to orbit the large near-Earth asteroid 433 Eros. • Near-infrared spectrometer All previous encounters with asteroids have been • Propellants: 320 kilograms • X-ray spectrometer quick flybys. From this vantage point in orbit, 710 pounds • Gamma-ray spectrometer NEAR will make the first comprehensive investi­ • Experiments: 60 kilograms • Laser altimeter gation of an asteroid's physical properties and sur­ 130 pounds face composition. The mUltispectral camera will • Magnetometer map Eros's fonn and color variations at 3-meter resolution. Mineral properties of Eros's surface will be mapped at 250-meter resolution with the near-infrared spectrometer. X-ray and gamma-ray spectrometers cause of a Discovery program guideline to use an inexpensive will measure the abundances of several key elements in the launch vehicle. With a larger launch vehicle, such as an Atlas sUTface layer, including aluminum, magnesium, iron, calcium, or Titan, a one-year direct trajectory would have been possible, sulfur, thorium, and potassium. These abundances will then be but the total mission cost would have been increased by at least matched to those of a variety of meteorite samples on Earth to $50 million. ascertain whether this type of asteroid could be the source for cer­ Rendezvous operations at Eros are scheduled to begin on De­ tain meteorite types. The magnetometer will address the question cember 20, 1998, with an initial close encounter (at a distance of of whether Eros has a magnetic field of its own. Data from the 500 kilometers, or 300 miles) occurring on January 10, 1999. laser rangefinder (lidar) will be used to detennine the shape and Later, as the spacecraft is maneuvered closer to Eros, NEAR will topography of Eros's surface to an accuracy of 10 meters. The lidar conduct science investigations from orbits that come as close as 15 determines the precise distance to the asteroid's surface by mea­ kilometers (9 miles). In the last two months of orbit, the minimum suring the time required for a pulse of light to travel to the asteroid's altitude will be lowered still further. Finally, on February 6, 2000, surface andrehJrn. Eros's mass and distribution of mass will be NEAR will attempt a soft landing on Eros. Since the NEAR determined while the spacecraft is in orbit; spacecraft tracking spacecraft was not designed to survive a landing, this maneuver measurements together with optical and tidar observations from should mark the end of the NEAR mission. By Valentine's Day the spacecraft will provide the necessary data. in 2000, NEAR will become a permanent fixture on the asteroid NEAR follows a circuitous three-year flight path to Eros be- named for the Greek god oflove. -RWF and DKY

colliding body would have just the right velocity (speed and Earth's rotation rate), but the time required for a moonlet direction) to stop the prior spin. According to Alan Harris of to slow Mathilde would be longer than the age ofthe uni­ the Jet Propulsion Laboratory, there is less than one chance verse. There is something very odd about Mathilde, and in a billion that the spins of three asteroids should be nearly the upcoming NEAR investigations should help explain stopped by random impacts. Harris notes that the situation is its peculiarities. analogous to asking a baseball player to bunt three fastballs so that the ball comes to a complete stop each time and Planning the Flyby drops onto the center of home plate. Once we established that there was only a negligible prob­ An undiscovered satellite orbiting Mathilde might slow ability of the NEAR spacecraft being crippled by a colli­ 6 its rotation rate by tidal forces (much as our Moon affects sion with a particle in orbit around Mathilde and that only a modest amount of extra fuel was required, the mission spacecraft camera images of Mathilde taken up to 24 hours team developed plans to optimize results from the fast before the encounter and should allow us to achieve the flyby. NEAR will encounter Mathilde on June 27, 1997. desired targeting accuracy. However, the strategy is At that time, NEAR will be roughly 2.0 AU from the Sun gutsy. The speed of the flyby does not leave much margin and 2.2 AU from Earth (AU = astronomical unit, the mean for error. distance between Earth and the Sun). Since the Mathilde flyby occurs almost 2 AU from the The first step in planning the flyby was to determine Sun, the power available from the spacecraft's solar panels accurately the asteroid's future path using ground-based is only about 25 percent ofthe maximum mission level. We'll observations of its past positions. We now have more than lose another chunk of available power because the solar 500 of these observations for Mathilde over the interval from panels, like the cameras, are fixed in position. In order for December 1, 1885 to July 23, 1996, with only 77 obtained (continued on next page) before 1994. Using these data, a conservative error analysis suggests that the uncertainty region in Mathilde's position at the time of the NEAR flyby will have a maximum extent of about 200 kilome- ters (125 miles). This uncertainty can be cut in half if high-precision radar observations of Mathilde can be carried out in early June 1997. Unfortunately, an uncertainty of200 kilometers is far too large. The spacecraft flies past the aster­ oid so fast that there is little time for the onboard na sense, the study of asteroids is a quest for our odgins. cameras to look around for their target. The search IWe think asteroids are leftover bits and pieces from the area must be reduced to a desired value of about formation of the inner solar system planets (including Earth), 25 kilometers (16 miles). Even using the cameras a process that took place some 4.6 billion years ago. These to provide a pre-encounter fix on the asteroid's objects may preserve clues to the nature of the matedal from true position might not solve the problem, because which the terrestlial planets accreted. Asteroids are a likely NEAR may not be able to detect Mathilde any source of most meteorites that strike the Emth, and some may earlier than 24 to 36 hours before the encounter. be ex-comets that have lost the vaporizing ices that once pro­ The late detection is due to the unfavorable direc­ duced their signature cometary atmospheres and tails. Asteroid tion by which the spacecraft approaches Mathilde. collisions may have delivered to early Emth the veneer of During its approach, the spacecraft will see just a volatiles and carbon-based molecules from which life formed. small portion of Mathilde's sunlit hemisphere so Subsequent collisions of a few good-sized asteroids with that the asteroid will appear only as a thin crescent. Earth could have periodically snuffed out some emerging life Taking pictures of a small object like an asteroid forms, allowing only the most adaptive species to prosper. during a fast flyby is extremely challenging for Even today, some asteroids are on Earth-crossing orbits and any spacecraft, especially one, such as NEAR, that offer a potential threat (albeit a very small one) to life as we does not have a movable camera platform. It would know it. Despite being some of the smallest members of our be like videotaping a billboard from a car that is solar system, these bits of interplanetaty flotsam likely played speeding along a multi-lane highway at night. If a critical role in the formation of Earth and the subsequent de­ you know exactly where the billboard is located, you could ask the driver to pass by very closely velopment oflife. To study asteroids is to study our own origins. while you move the camcorder at just the proper Most asteroids have been classified as so-called S-types or angular rate. However, if you don't know precisely C-types. Astronomers classify asteroids by their ability to re­ where the billboard is-or its height above the flect light in various wavelengths (that is, by their spectral ground- you'd be better off observing from a characteristics). The most common type in the inner pact" of greater distance, panning the camcorder back and the asteroid belt is the S-type, whose ability to reflect light forth to cover the entire region where the billboard generally increases as wavelength increases from 0.4 to 1.2 might be located. Your optimum strategy would be microns (micron = 0.000039 inch). In the outer asteroid belt, to pass as close to the billboard as possible to get the much darker C-type asteroids dominate, and their signature the best look but still keep far enough away so you is that they reflect light nearly equally at all wavelengths be­ could sweep the entire uncertainty region, ensuring tween 0.4 and 1.2 microns (that is, their spectra are relatively that you would get a picture of the target. flat and featureless). In an analogous fashion, NEAR can get to within Neither the S-type nor the C-type asteroids have been defi­ 1200 kilometers (750 miles) of Mathilde's pre­ nitely identified as parent bodies for any meteodtes on Earth. dicted position and still have the ability to make Some scientists believe that the most common meteorites, the the panning motions that will ensure the camera ordinary chondrites, odginate as collision fragments from the has captured a series of close-up pictures of S-type asteroids in the inner belt. Another group of scientists Mathilde. Because the NEAR camera is fixed to thinks there is no familial relationship. As a result, a major the side of the spacecraft, the entire spacecraft, not objective of the NEAR mission is to match the chemical com­ just the camera, must slew to observe the asteroid. position of Eros against that of the ordinary chondrite meteorites Our current plans call for a spacecraft trajec­ or another meteodte type. The results of the NEAR mission tory correction maneuver just 12 hours before should provide evidence as to which meteodte types, if any, closest approach. This maneuver will utilize began life as a piece of an S-type asteroid. - RWF and DKY 7

H "

NEAR Trajectory Profile together like a rubble pile. A higher density, similar to solid rock, would suggest that Mathilde was formed as a chip off an old block, a fragment of a larger body that was disrupted by a collision with another ...... -. -..... asteroid eons ago. -...... '...... ~ We will use the camera system to deter­ DEEP SPACE mine the approximate shape of the asteroid ",- 433 EROS···. MANEUVER and hence its volume. Unfortunately, EARTH ORBIT \" 7/3/97 since the asteroid rotates so slowly, it ORBIT • will present only one side to the passing spacecraft. We have preliminary plans to use ground-based radar to help determine the volume of the asteroid. Steve Ostro : MATHILDE FLYBY and his colleagues have demonstrated that 6/27/97 radar observation campaigns can provide EROS ARRIVAL : detailed information on an asteroid's size __ - -1/10/99 and shape. . We'll determine Mathilde's mass by . accurately tracking the NEAR spacecraft ....:f before and after the encounter. During the flyby, Mathilde's gravitational attraction .. ' .' .' will exert a slight tug on the spacecraft, changing its velocity by about 3 millimeters per second (0.1 inches per second) and bending its flight path by 0.00002 degrees. One hour after the flyby, when the space­ craft has traveled another 36,000 kilometers (22,000 miles), it will have deviated only 12 meters from its nominal path. Gravita- the camera to point at Mathilde during the flyby, the solar tional tugs on Galileo were far too small to allow a mass panels must face about 50 degrees away from the Sun. determination for asteroids Gaspra and Ida. However, Because of this very constrained power condition the only Mathilde's mass is likely to be much greater than that of science instrument we will operate during the encounter is either Gaspra or Ida, so its effect on the NEAR spacecraft's the multispectral camera. However, we can use spacecraft path should be detectable in the radio tracking data. tracking data before and after the encounter to determine According to a recent analysis by Dan Scheeres ofthe the asteroid's mass. Jet Propulsion Laboratory, Mathilde's mass should be determined to an accuracy of about 5 percent. Encounter Science The flyby of asteroid 253 Mathilde is an important and We have three major objectives for the NEAR camera ex­ challenging segment of the NEAR mission. To achieve periment during the flyby. Most important is that we get our major science objectives, we will have to continue at least one image of Mathilde near closest approach to refining our knowledge of Mathilde's orbit from precise provide the most detailed view possible of the surface. Our ground-based'observations. As the moment of encounter second requirement is to obtain an image that includes as approaches, we'll have to be ready to use NEAR.images of much of the sunlit side as can be seen from the spacecraft's Mathilde to assure that the cameras will be properly pointed perspective. Third, we want to search the sky around the at their target at closest approach. asteroid for possible satellites. The Mathilde flyby will complement the Galileo flybys The entire imaging sequence will be accomplished with­ of Gaspra and Ida in important ways: it will be the first in about 30 minutes of closest approach, totaling about close-up study of a C-type asteroid, and it will be the first 300 images. The cameras will image the whole illuminated time such a study is carried out by a spacecraft without a portion of the asteroid in color, resolving features as small movable camera platform. The results obtained will not as 500 meters. The best partial views will also be in color only provide an important test of the NEAR camera but will with resolution down to 200 to 350 meters. permit us to assess fundamental differences that may exist Another primary science objective during the flyby between C-type asteroids and S-objects, of which NEAR's will be to estimate Mathilde's bulk density, a quantity that main target, 433 Eros, is representative. However, as is requires determining the asteroid's volume and mass. The normally the case for interplanetary encounters, the most bulk density of Mathilde is important in discerning its origin. interesting results will take scientists completely by surprise For example, is this asteroid a single large fragment from as the NEAR spacecraft waltzes by Mathilde. a collision of two larger asteroids, or is it a collection of many smaller fragments-fragments that resulted from Robert W Farquhar of the Johns Hopkins University 's repeated collisions of many different typcs of asteroids? A Applied Physics Laboratory is the NEAR Mission Director. low density for Mathilde would suggest that it was formed Donald K. Yeomans ofthe Jet Propulsion Laboratory is the 8 as a collection of several distinct fragments held loosely Team Leader for the NEAR Radio Science Experiment. twas March, 1972. Viet­ All four of our escaping emissaries nam's agony dragged on are powered by plutonium, whose LJ while a fatal corruption inexorable decay heats thermocouples seeped into the campaign for re­ to make electricity on board. Over election of President Richard M. the years this power will fade. Still, Nixon. Threatened abroad by the the Voyagers are expected to continue Soviet Union and embittered by reduced operation well into the next dissension, Americans can perhaps century. Not so, Pioneer 10. Soon be forgiven if we hardly noticed the Pioneer 10 will receive an irrevocable launch of one more spacecraft. On command to shut down, its funding March 3 began a journey like none spent, its duties ended, and its small other. For the first time in the long share of tracking time on the Deep climb of homo sapiens from a mys­ Space Network released for other tery-shrouded past to an unknowable uses. Pioneer 10 will drift onward future, we launched an object whose silently, its motion governed by the ultimate destination was the stars. law of universal gravitation, while Now, 25 years later, Pioneer 10 hurnan generations come and go, is the first of four such artifacts, and civilizations rise and fall. spacecraft that have left us forever, Though we will probably forget escaping not only the gravity of Pioneer 10 as our busy little ant­ Earth but also that of the Sun. With like lives go on, Earth's first stellar its fellows, Pioneer 11 and Voyagers emissary cannot forget us. In its 1 and 2, flung onward by giant engineering details, it will forever Jupiter, Pioneer 10 is outbound to reveal that somewhere in the cosmos interstellar space. there were mathematical beings who During its decades of exploration could win and work metals, gener­ Pioneer 10 has returned reams of ate radio signals, and call down the data about interplanetary phenomena, Promethean [lIe of the nucleus. And '\ 1JS> including the first measurements more: Pioneer 10 carries the first near Jupiter defining that planet's message from us, intended to prove enormous magnetosphere and its that there was, at our time and place o o " ~~o deadly radiation and particle environ­ in the universe, an intelligence that lop: PIOneer 10 flllas fhe fifst.splJCeCraft IauJltIIed ments. Now Pioneer 10 probes out­ knew something of nature and some­ on a traj~taklnglt o~ ofour$Olafsystem. ward toward that vast, fluctuating, thing of itself. The golden plaque, Middle: On IJeteltilJqr3, 1([13, PIO!l\Ier 10 IJecaJne diaphanous edge of the solar domain installed at the urging of Carl Sagan the tfrst spacecraft ,to f!y by-the planet JI1pitI1r; where at last the ever-expanding and drawn by Linda Salzman, Bottom: The spacecrattcarrles a plaque beating a message to any civilization that might find it wind of magnetism, gases, and rides on Pioneer 10 toward what­ COf/nterclockwise from top lefta-re a schematic ofa particles from the Sun is turned ever destiny awaits it in star space hydrogen atom, a- pulsar map containing information back by the interstellar medium. and time. Oil" the locatioll" and time of launch, a diagram of This is the boundary of the helio­ Pioneer 10' s homesola-r system, Bndtwo represen­ tations of its creators, standing in front of the sphere, the end of our neighborhood James D. Burke is Technical Editor parabofic antenna they used to communicate with in space. afThe Planetary Report. their creation, Images: NASA/Ames Research Center 9 ~S HER SEC BY CHARLENE M. ANDERSON

oes she or doesn't she hide an ocean beneath comes from tidal tugs from Jupiter and the other large that enigmatic face? That is the question moons in the Jovian system. This same mechanism planetary scientists- and oceanographers and drives the volcanoes of 10. If tidal forces are reshap­ biologists-are asking about Europa , the second ing the face of Europa , the question remains whether D Galileo r large moon of Jupiter. As gets closer and these forces could provide enough energy to sustain closer in, some features the spacecraft sees suggest a subsurface ocean and some form of life. there may be liquid water close to the surface. Other Within these detailed images, Galileo scientists details indicate it may be more mush than liquid. No find evidence that the energy source has reworked one can yet say for certain what lies below, but there the moon's surface recently. Ridges are broken off, is hope-"hope" being a word not usually used in like freeway overpasses after an earthquake. Flows of scientific contexts-that Europa does possess an thick, viscous ice have erupted from below, obliterat­ ocean. And where there's liquid water-and organics ing the linear features in some spots. Many regions and an energy source-there may be life. have very few or no visible impact craters, indicating On these pages you can see the latest images of that they are young. The water must have flowed Europa, taken on Galileo's fourth orbit around Jupiter. within thelast few thousands or millions of years­ The spacecraft had looked at this moon during its the recent past, in geologic time. This is good news close encounters with Ganymede and Callisto, the for those looking for a subsurface ocean. outermost large satellites, but the best pictures But within these images the Galileo team also then showed details only as small as 1.6 kilometers found a large circular feature that looks remarkably (1 mile) across. We now have pictures with details like an impact basin. If a liquid ocean exists beneath as small as 36 meters. And, as we see smaller and a thin ice crust, it would be hard to explain how a smaller details, Europa looks weirder and weirder. large impact basin could remain to scar the surface. From Voyager images taken 18 years ago, we Scientists can't be sure the feature is an impact knew that Europa was crisscrossed with strange basin-it also resembles the coronae seen in Magel/an linear features. Galileo revealed these to be ridges images of Venus. Coronae are circular features com ­ and grooves, some stretching across hemispheres. posed of concentric cracks that probably form when They have proven to be the dominant topographic form magma pushes up on a pliable surface but doesn't on Europa, and we are now seeing them down to the erupt through it. The jury is still out on this feature. limit of resolution. The ridges probably form as viscous To make sense of Europa's face, scientists will have materials erupt through cracks in the icy surface. In to see more of it. As Michael Carr of the United States some instances, the eruptions occur repeatedly, form­ Geological Survey said, "We 've seen so little, it's hard ing multitudes of parallel ridges and grooves within to make grand interpretations." More data are coming. the lineaments. The best earthly analogy for this pro­ In late February, Galileo again flew by Europa and will cess would be mid-oceanic ridges, where magma from soon return new images. With more information , scien­ beneath the crust erupts again and again, adding to tists will be better able to unravel the moon's enigmas. the margins of the tectonic plates that make up our Ronald Greeley of Arizona State University, head of planet's crust. But this comparison is not exact, for the Europa team on the Galileo project, indicates on Europa the crust is primarily water ice, not rock. that, with rega rd to the ocean, they will be addressing 10 The energy to drive tectonism on Europa probably three principal questions: 1. Is there any liquid water beneath the surface? But even after GEM, it's possible that we won't 2. Is it confined to local hot spots? know for certain if Europa has an ocean. We may need 3. Is it a global ocean? to land on this moon with geophysical instruments Whether or not Europa does possess an ocean-and derived from equipment used by oceanographers on harbor the potential for life-it is one of the most fasci­ Earth. Last fall a group of ocean scientists gathered nating worlds yet visited by humanity's exploring space­ with their planetary counterparts at the San Juan craft. Recognizing this attraction, NASA has committed Capistrano Research Institute in California to discuss to extending the Galileo mission beyond its scheduled strategies for exploring Europa. This little world is end in December 1997. After that date, controllers will proving to be one of the most fascinating bodies in direct the spacecraft to lower its orbit about Jupiter by our solar system. So much is possible there, and there making several close passes by Callisto. During the is so much left to explore . . . Galileo Extended Mission (GEM), the spacecraft will get into position to swing by Europa again and again, each Charlene M. Anderson is Director of Publications for time adding details to our picture of this weird world. the Planetary Society.

] E L E ? Are there ice volcanoes on Europa? In this image, scientists see features that look remarkably like terrestrial volcanic features-but, of course, on our planet melted rOCk, not water, creates the features. To the upper left of center, a dark feature very much resembles volcanic vents on Earth. In the lower left, too, a parallel pair of vents appears. In terrestrial examples, we often find vents of this kind associated with lobate flows of thick, slow-moving lava. Just below center in this image, a lobate flow has obliterated a ridge. Galileo took this image from a distance of 62,000 kilometers (39,000 miles) from Europa, resolving details as small as 1.6 kilometers (1 mile) across. This image covers an area 126 by 393 kilometers (78 by 244 miles). Image: JPUNASA Is this an impact feature, the healed-over scar formed when some object punched through the thin icy crust to the mush beneath? Or is it a volcanic feature, formed when a plume of heated material pushed upward, leaving concentric rings on the disrupted crust? The answers to these questions could be critical to under­ standing the processes going on beneath Europa's puzzling surface. This feature, called a macula, is large, some tOO kilometers (60 miles) across. It would be difficult for a thin ice layer over an ocean to retain the concentric rings associated with impact basins, such as those on our Moon and Mercury. Scientists don't yet know enough about this feature to say exactly what it is. They can, however, say that it is relatively young, for this macula overlies the ridged terrain seen to the left and bottom right. This image covers an area 48 by 91 kilometers (30 by 57 miles), with details visible down to 240 meters across. It was taken from a distance of 11,933 kilometers (7415 miles). The black lines in these images are artifacts of processing.

Imagine now that you are riding on Galileo as it closes in on Europa, swinging through its fourth orbit around Jupiter. From the distance of 62,000 kilometers (39,000 miles), you see the network of crisscrossing ridges that dominate the satellite's surface. Some ridges seem to have been broken or swept away by volcanic flows-and on this icy world, the volcanic flow is probably water. No obvious signs of impact craters catch your eye, so you conclude that this region is relatively young, and whatever processes created it have been active in the recent past. This view takes in an area 126 by 393 kilometers (78 by 244 miles), resolving details as small as 1.6 kilometers (1 mile) across. Your trajectory will soon bring you in for a closer, more detailed look at the region outlined in the upper left.

12 This close-up of the region just to the right of the macula reveals several small craters, which may mark sites where debris fell after the impact that formed the ringed basin-if indeed the ringed basin is an impact feature. The ridges that dominate so much of Europa's surface are well represented here, looking much like freeway systems on Earth. Look particularly closely at the ridges just to the right of center, halfway toward the bottom. A dark zone appears to the right of one of the most prominent features, showing that something has recently wiped out some ridges. Underneath lies a disrupted ridge reminiscent of freeway overpasses broken in earthquakes. The region here, covering an area 48 by 91 kilometers (30 by 57 miles), shows details as small as 240 meters across. This image was taken from a range of 11,850 kilometers (7400 miles).

You've now zoomed in on the second panel from the top in the image at left. This is the most detailed view ever taken of Europa, revealing features as small as an earthly football field. In the center, you see where flows of icy material Now you're only 3400 kilometers (2100 miles) away, and you're struck by the have obliterated the distinctive ridged terrain. complexity of Europa's surface. At the top left, you see how the parallel ridges To the right is knobby terrain of unknown origin. have been broken and offset by movement in the surface layer. Lower down in Small craters, from about.100 to 400 meters the image is chaotic terrain, where the ridges have been destroyed. Below that across, dot the frame, but whether they're scars you note some excellent examples of broken ridges. The landscape at the bottom of collisions with asteroids and comets or of the image demonstrates how the parallel ridges form. Water, probably carrying remnants of some internal Europan process, silicate and sulfurous materials, erupts through long, linear cracks in the surface no one can say for certain. Everything about this and oozes to either side. In some cases, the eruptions continue, with newer moon is strange, intriguing, elusive-it must ridges pushing.aside older ones. Eventually, long and broad lineaments cover be seen again and again before we'll have a large areas of the Europan surface. On Earth, scientists have watched similar chance of understanding the inner workings of processes forming the mid-oceanic ridges, where molten rock erupts to the this mysterious world. surface, creating new crust. In this image, you can see details as small as 70 Galileo took this image when the spacecraft meters across covering an area 17 by 49 kilometers (11 by 30 miles). was only 3340 kilometers (2075 miles) from Europa's surface, showing an area 9.6 by 16 kilometers (6.0 by 10.0 miles). Images: JPUNASA

13 Consider all we have to work with: • the continuing discoveries of planets around other stars; • the discovery of possible ancient Martian life; • two missions, Mars Pathfinder and Global Surveyor, on their way to explore the most Earth-like of planets; • an ambitious and daring program to launch spacecraft to Mars at every opportunity; • the Galileo spacecraft doggedly returning amazing data, despite a crippled antenna, from Jupiter and its moons; • hints of a liquid water ocean beneath the frozen crust of Europa, one of Jupiter's largest moons; • the Near-Earth Asteroid Rendez­ vous spacecraft preparing to fly by Mathilde on its way to its target, Eros; • the Cassini mission preparing to explore Saturn, its rings, and its tanta­ lizing moon, Titan; and • active searches, by the Planetary Society and its allies, for radio signals from possible extraterrestrial civiliza­ tions. This is the tinder to light again the fire for exploration in Earth 's peoples. Better than anyone else, Carl knew how to spark our desire to see and understand the wonders of the universe. A churning, As an organization, it falls to us to violent, continue his work. luminescent, As an organization, the Planetary and transcendently Society must change and grow to meet beautiful this challenge. Indeed, having this chal­ birthplace of lenge placed before us gives us both stars, the incentive and opportunity to improve and Orion Nebula is only 1500 strengthen the Society. And so, we turn light years to our members for help and support. from Earth. he loss of Carl Sagan has filled all of us in the We ask you to share your thoughts on what actions we Image: Planetary Society with deep sadness, but it is a should take in the next few months and years. How should C.R. O'Oellof sadness tempered by hope. We have come to we direct our energy? What roles should we play in advo­ Rice Universityj T Hubble Space see that the future among the planets we envisioned, with cating and, where possible, enabling planetary exploration Telescope, Carl's guidance, is within our grasp. Through his dedica­ and the search for life elsewhere in the universe? Are there NASA tion and enthusiasm, the joy and wonder of exploring our activities we should drop to better focus our efforts? neighboring worlds and searching for extraterrestrial life How do we encourage other people and organizations to have been conveyed to millions who inhabit this world. join us? Carl left a world ready and able to venture outward and Many other questions facing our organization may occur to accept the great challenges posed by the universe to you, and we would like to hear them and your ideas on around us. how we should proceed. In this time of combined sorrow, This is Carl's legacy, and it is our task to build upon it. hope, and opportunity, if we work together we can create a So as a society of like-minded people, with a wide array stronger, more effective force to achieve our shared goals. of talents, how do we direct our energy as we continue The solar system and the galaxy lie before us. We can help Carl's work and expand his legacy? How do we galvanize determine how hun1anity rises to the challenges they pose. individuals and institutions around the world into under­ taking the great challenges? How do we grow our organi­ Bruce Murray, Professor ofPlanetary Science at California zation into a force capable of leading the endeavor of Institute of Technology, is Vice President of the Planetary 14 planetary exploration? Society. Louis D. Friedman is Executive Director. ------~~======r_-'I

World

lNatch by Louis D. Friednlan

Europe- The loss of Mars '96 was and missions relying on innovative government for science programs and a major blow to European planetary ex­ technology. their space agency has resulted in de­ ploration as major participants France, lays in the space station program­ Germany, Italy, and Finland lost about Japan-Japan plans to launch its delays affecting the US program and $200 million on their instruments and first mission to land on another world­ cooperation between the two countries. other commitments to the mission. Lunar A- in August 1997. Whether this But not all of the news is bad. Russia's Earlier in the year, the European Space date can be met will depend on results 1997 budget, while allocating less to Agency (ESA) had rejected plans for of a trial launch of the M5 rocket. In space exploration than requested, was InterMarsNet, a cooperative mission 1998, the Japanese plan to launch 12 percent higher than in 1996. with NASA to be launched in 2003 on Planet B, an aeronomy orbiter, to Mars an Ariane rocket. Now they have no (see the November/December 1996 Washington, DC-With the Mars program. Planetary Report). extraordinary interest in the possible In addition, ESA's science program On the horizon are exciting plans for Mars life discovery and the stellar faces a 15 percent budget cut over the developing a near-Earth asteroid mis­ performance of NASA science missions next five years- in its already approved sion, Muses C, to launch in 2002 and in the past year, there is hope that program. This is the first time ESA has return a sample to Earth in 2006. The projected declines in funding will be had to absorb so large a cut. target is asteroid Nereus, discovered by averted. With the Near-Earth Asteroid The failure of the Ariane 5 launch astronomer Eleanor Helin as part of the Rendezvous, Mars Pathfinder, and of Cluster- four Earth-orbiting space Society's asteroid research program and Mars Global Surveyor on their way science satellites- produced another named by a Society member. and Galileo and the Hubble Space financial blow to ESA. Funds to refly Japan's two space agencies, ISAS Telescope returning exciting results the mission are being sought. and NASDA, are getting together for practically every day, NASA's space But European space science also saw the first time to conduct a lunar mission, science program enjoys a level ofpopu­ major successes in 1996. The Infrared tentatively scheduled for launch in 2002, larity and political support not seen . Space Observatory and Solar and known as Selene-the Selenological and since the 1970s. Heliospheric Observatory, two Earth­ Engineering Explorer. Budget cuts are expected in fiscal orbiting astronomy satellites, have been Japan has produced a long-range year 1998. The pressures on NASA spectacular performers. space development plan that includes remain enormous. Program resiliency, For this year, Europe has the Huygens programs for a course of lunar explo­ the ability to respond to unexpected atmospheric probe aboard the Cassini ration resulting in a robotic lunar base, difficulties, gets squeezed when money mission. Rosetta, a comet rendezvous perhaps by the year 2025. is tight, and so does the agency's ability mission, is scheduled for launch in to respond to new initiatives, such as a 2003. The Europeans are considering Moscovv- Russia is looking into Mars sample return, the Pluto Express, several proposals for reflying their Mars '96 reflight alternatives, including and follow-up investigations of Europa 'Mars '96 instruments, though no partic­ smaller launches of different parts of and the outer-planet satellites. ular spacecraft or launch opportunity the payload, international cooperative Planetary Society members will soon has been identified. ventures, or simply moving on to other receive special mailings and appeals to With national agency budgets going missions. The United States has asked advocate government support for space down and ESA budget pressures Russia to endorse "Mars Together" and exploration missions in the US and in continuing, there's impetus for major a plan to launch a Marsokhod rover in other nations. changes in European planetary programs, 2001 that would send data via the US such as new cooperative ventures with Mars Global Surveyor orbiter. Louis D. Friedman is Executive Director the United States or smaller satellites Weakening support by the Russian of the Planetary Society. 1S Basics of Spaceflight:

Encf-to-End Data FloIIV­ The DOIIVnlink Part

by D.,.'Ve Doody

hiS installment, together with the preceding one images, spectra, and other data, which then go to a storage on uplink, offers a large-scale view of how uplink device aboard the spacecraft, such as a tape recorder. r and downlink work together as a system, bringing That device, under the control of a computer, plays back measurements of distant objects in the solar system to our the information when Earth is listening. Hardly a bit of front doors and to our home computers. precious science data is ever lost permanently. If informa­ Uplink refers to radio signals sent to a spacecraft; down­ tion gets garbled on the way down- because of a rainstorm, link is a transmission from the spacecraft to Earth. Once an for example, over the receiving station of the Deep Space uplink has been sent and its commands carried out by the Network (DSN)-controllers can command the spacecraft spacecraft, two kinds of results come back on the downlink. to replay the data when Earth rotates a drier DSN station One is telemetry, meaning onboard measurements that into view. have been converted to radio signals. The other includes The downlink radio signal is pretty weak, having traveled tracking and radio science data. a long distance. It takes large-aperture radio telescopes to The downlink contains both engineering and science collect and concentrate the signal. The antenna has to be information. Engineering telemetry, for example, includes pointed in exactly the right direction to locate the space­ the temperature of nearly every spacecraft component as craft in the sky. Once the downlink signal has been funneled well as voltages, currents, pressures, and other measure­ in, we boost it in the antenna with a low-noise amplifier ments. Engineers rely on these measurements in their kept at very low temperature to minimize electronic noise. operation of the spacecraft. Tracking and navigation data From the low-noise amplifier, the signal goes to a radio (described more fully in the July/August 1995 Planetary receiver that automatically tunes in the right signal. Once Report) fall under the engineering heading, too. the receiver has locked onto the downlink, the signal goes Under the science heading we include data from the to a telemehy processor, which converts the signal to binary science instruments and imaging equipment (which are digits (bits), all ones and zeros, the same digital information telemetry) and the radio science data. In a radio-science originally generated by the spacecraft instruments. The experiment, the downlink may yield atmospheric-sensing DSN transmits these telemetry bits to JPL via the Ground results or provide tracking data to determine the mass of a Communications Facility (GCF), which despite its name planet or moon. relies on satellItes for communications. In addition to Transmission of science data, whether telemetry or telemetry, the DSN captures tracking data and rad~o science radio science, enjoys the highest priority in the end-to-end data. In the diagram, we see data coming in to JPL, where system. Engineering data have a repetitive nature: if some preliminary processing removes GCF transport information information is lost, it's usually no big deal, because the and decommutates the channels. same measurements will probably recur in a short time. Decommutates the channels, he said! Remember, a Science is the diamond amid rhinestones. Its receipt is the spacecraft sends lots of engineering and science measure­ purpose of flying spacecraft in the first place. ments. Decommutating means determining the kind of data being received. Channels are categories of data. For exam­ HOIN'Mfe Lisl:en ple, instead of always referring laboriously to "the temper­ A broad definition of downlink encompasses receiving, ature data on reaction wheel motor number one," we just deciphering, storing, distributing, displaying, archiving, and call it something like "Channel E-1654." E-channels are publishing the data. The result of the end-to-end system is for engineering data, and S-channels are for science data. that science data reach the worldwide public, including the people who fund missions with their taxes. TDS Hss Re_sull:s The diagram on the next page depicts a typical Jet RighI: No"" PropUlsion Laboratory (JPL) project, such as Galileo, Mars The telemetry, now "channelized" to identify its contents, Global Surveyor, or the soon-to-launch Cassini mission is typically stored within a Telemetry Delivery System to Saturn. Many of the components pictured are shared by (TDS) for the entire life of the mission. TDS distributes several projects. Going from left to right, the diagram telemetry to people who should receive it right away: the 16 shows that the spacecraft's scientific instruments collect real-time flight controller who is looking out for surprises, End-f:o-End DOlNn'ink F'olN

SPACECRAFT .'\~ JPL GROUND COMMUNICATIONS FACILITY INTERFACE TELEMETRyl------...,..--.,...-+-..,-----, ~1@x ~~~~====:F_ --->o..- DELIVERY SPACECRAFT ENGINEERS /" --- SYSTEM AND CONTROLLERS .... & PROCESSI G I~I I~I I~I IIml:l:ml ~ w:m:m:II

MOSTLY ENGINEERING DATA

YOU ARE HERE WORLDWIDE e GENERAL PUBLICATION 1111111111111111•

CHART BY DAVE DOODY; MODIFIED BY B. S. SMITH

the engineer who needs to watch a propellant tank tempera­ data via the Planetary Data System, which consists of a ture, or the scientist waiting for findings from a particular central on-line catalog and data retrieval nodes at various instrument. research facilities. TDS users can custom-order the telemetry they need. Classroom educators can obtain videocassettes and a For example, a science team analyzing data from a photo­ wide variety of other materials on NASA's flight projects polarimeter experiment might need to look at radio-receiver through Educator Resource Centers (which until just perfonnance to be sure oftheir results. Another supplementary recently were called Teacher Resource Centers). data set includes spacecraft and planetary positions and in­ Flight projects are making increasing use ofthe World strument pointing. With this infonnation, we can detennine Wide Web to disseminate preliminary images as well as exactly where in space the data were gathered from and full scientific results: this is a "high leverage" avenue, thus where they fit in relation to other collected data. meaning that a very large number of people can be served Once a team of scientists has correlated and analyzed the with a minimum investment of resources. Be sure not telemetry and supplementary data, they will want to publish to miss Galileo and other Web sites accessible from their results in a scientific journal, but even before these www.jpl.nasa.gov. scholarly articles appear, the public gets a look! NASA If you don't normally have access to the Web, come policy calls for immediate publication of images returned to Planetfest '97 in Pasadena this July and hook in via from planetary encounters (represented by the dashed arrow the high-speed Internet browsing computers that will be in the diagram). These "first-look" images are preliminary available. and usually lack the high resolution scientists need for In the next installment, we'll take a good look at the . extensive analysis and reporting. Deep Space Network. Without the incredible capabilities of the DSN it would be impossible to accomplish any SerV'JDg a l/JT'OrJd '0' planetary exploration at all. D :ata C _on,surr.r.ers Data from planetary missions are made available worldwide Dave Doody is a member ofthe Jet Propulsion Laboratory's through Regional Planetary Imaging Data Facilities, operated Advanced Mission Operations Section and is currently by NASA at more than a dozen sites around the United working on the Cassini mission to Saturn. States and overseas. Each maintains a complete photographic library of images from lunar and planetary missions. These If you have access to the World Wide Web sites are open to the public by appointment for browsing (via a Web browser like Netscape or Mosaic), be sure to and ordering materials for purchase. look in on JPL' s Basics ofSpace Flight manual, on-line at Researchers funded by NASA obtain planetary imaging http://www.jp1. nasa. govI basics/. 17 News and

Revievvs by Clark R. ChapnlIan

uropa, Jupiter's second moon, gaze, and we will finally learn whether with only a thin water-ice crust. With has been much in the news of to expect even richer wonders beneath gravity data already sent home, and E late. A recent Galileo image of its surface. more to come, Galileo may soon treat Europa graced the cover of Discover's us to further surprises. January "Year in Science" issue. NASA Jack Frost"s Artistry has given the go-ahead for a Europa­ At a January 17 press conference at Extrasolar Europas? intensive continuation ofthe Galileo NASA Headquarters, Galileo researchers Let your imagination take wing, and mission. And there has been much public released close-ups of a landscape like consider those recently discovered speculation about a possible ocean, even no other in the solar system. On a scale Jupiter-like planets in Earth-like orbits life, on this baffling body. of meters to kilometers, nature has around other stars. Until now, the The classic textbook Astronomy by etched a geometric pattern of icy features search for extraterrestrial life has con­ Henry Norris Russell, Raymond Smith as unexpectedly intricate as Jack Frost's centrated on the concept of Earth-like Dugan, and John Quincy Stewart, icy patterns on our window panes. The planets around the billions of stars that published 70 years ago, reports that the freeway-like ridges of ice sometimes might have their own solar systems. diameter of Europa is 3150 kilometers intertwine as though they were created As Russell, Dugan, and Stewart wrote (or 1960 miles, a bit smaller than the by a cosmic basketweaver. 70 years ago, "Here and there, at least, Moon), that its surface is very bright, Craters are scarce on Europa's surface, among these there should be planets that it keeps one face to Jupiter, and that raising the possibility that active water­ large enough to retain an atmosphere, it is made mostly of rock-different ice volcanism may still be occurring on with water upon their surfaces, and at from the much icier compositions of its surface, with eruptions of water from such distances from the stars about Ganymede and Callisto. The only thing below keeping the icy surface fresh and which they revolve that their surfaces learned from the next 50 years oftele­ bright, despite the black rain of cosmic are maintained at a genial temperature." scopic observations was that Europa's debris. Indeed, Arizona State University Now Darren Williams, James Kasting, bright surface is, indeed, due to water researchers Ron Greeley and Rob Sulli­ and Richard Wade of Pennsylvania State ice. Theoreticians then speculated that van have reported tantalizing evidence of University, writing in Nature for 16 there might be a shallow mantle (or ice volcanoes and smooth glacier-like January, ask us to imagine what Europa "ocean") ofliquid water beneath the ice, flows on the otherwise tortured surface would be like if its parent planet were but the picture of Europa as an essen­ of Europa, keeping alive the idea ofa as close to the Sun as the Jovian com­ tially rocky body remained unchanged. subsurface ocean. panions of 16 Cygni Band 47 Ursae Voyager 2's flyby in 1979 revealed a But it is notoriously difficult to prove Majoris. In a comment on their article perplexing network oflines on Europa's what lies within a body that can only in the same issue of Nature, Chris nearly craterless surface that resembled be observed from the outside. If you Chyba of the University of Arizona Percival Lowell's fanciful network of didn't know already, would you ever pays tribute to Carl Sagan's pioneering Martian canals. But the spacecraft was guess- from the external appearance work in this field. With a Saganesque too far away to tell us anything more of a banana peel- what the fruit inside flair, he questions the chauvinism of about Europa's geology or its interior. is like? Just how thick is the ice on the criterion that habitability necessarily After allowance for Voyager's margin Europa? Lacking instrument data that involves surface liquid water. of measurement error, Europa's size would give a definitive answer, Brown Who can say how narrow, or broad, remained exactly as given by Russell, University geologist Jim Head draws is the range of conditions sufficient Dugan, and Stewart. In the 1980s, several an evocative analogy: ifhe saw a for the origin and sustenance oflife? researchers debated whether or not there frozen-over New England pond that Practicality dictates that we explore the was a subterranean ocean on Europa. looked like Europa, he wouldn't dare question one step at a time. Mars and Last December 19, as Galileo flew to skate on it! What we really need is a Europa appear to be next in line. within 700 kilometers (400 miles) of its network of seismometers on Europa to surface, Europa remained an enigma. probe its interior. For now we at least Clark R. Chapman, who took Carl Sagan 's Slowly, but surely, during the next have Galileo, whose close flybys will course on "The Planets " in 1965, is three years, Europa's veil of mystery soon take us beyond the standard guess researching Europa as a member of the 18 will be lifted under Galileo's intense that Europa is basically a ball of rock Galileo Imaging Team. Society Ne1NS

Planetfest '97 Takes Off colleagues, as well as the entire Plane­ VielN the '98 Eclipse Plans are well underway for Planetfest tary Society staff, have made this possi­ The Planetary Society is offering two '97, taking place July 3-6 at the Pasadena ble," says Guillermo A. Lemarchand, a tours to view the total solar eclipse Convention Center in Pasadena, Califor­ researcher at the Argentine Institute for that will occur February 26, 1998. A nia. An enormous variety of exhibits and Radioastronomy and editor of the Plane­ Caribbean cruise and a land tour to Aruba, displays will fill the convention hall, in­ tary Society's Bioastronomy News. "We which includes an optional visit to the cluding the Mission Status Board and would particularly like to thank all Plan­ Ariane launch site in French Guiana, Video Wall, a state-of-the-art projection etary Society members whose generosity will provide rare viewing and photo­ system that will follow the historic July 4 allowed us to continue with the project." graphing opportunities of the three­ Mars Pathfinder landing as it happens. - Bill McGovern, Production Editor minute-forty-five-second event. Space The Hall of Technology will feature is limited and will fill up quickly. For exhibits of technological innovations Crater Chasing in Belize more information and a free brochure, in space science and exploration, and A The Planetary Society is organizing an­ contact me at Society headquarters or Child's Universe will showcase hands­ other expedition in our Cretaceous­ bye-mail: [email protected]. on fun, including the Society's popular Tertiary (KIT) series of searches for evi­ -Susan Lendroth, Red Rover, Red Rover Project. Movies, dence of the impact 65 million years ago Manager ofEv ents and Communication art, and books, plus exciting presentations, that led to the extinction of the dinosaurs. discussions, and debates by some of the Slated for January 1998, the expedition We Need Your Help world' s leading scientists and thinkers to central and southern Belize will Sign up now to take part in the Planetary will all be part ofthe four-day space attempt to determine the extent of ejecta Society's Planetfest '97, July 3-6, 1997, celebration. For information contact me deposits from the Chicxulub crater and at the Pasadena Convention Center in at Society headquarters or bye-mail: their stratigraphic relationships. The Pasadena, California. We need volunteers tps.cj @mars.planetary.org. expedition is limited to 12 participants to hand out information, take tickets, - Cindy Jalife, Planetfest Coordinator and will cost about $2300 per person, check badges, operate slide projectors, excluding airfare. For information, contact navigate the World Wide Web, build META II Restarts SETI me at Society headquarters or bye-mail: water rockets, tally sales orders, and assist The Mega-Channel Extraterrestrial [email protected]. in many other areas. For information, Assay (META) II project, which has been -Lu Coffing, Financial Manager contact Volunteer Coordinator Carlos searching for signs of extraterrestrial Populus at Society headquarters or by intelligence (SET!) from Earth's southern Test Balloon Explodes e-mail: tps.cp @mars.planetary.org. hemisphere, is once again in operation. A prototype Mars balloon constructed -SL The system was shut down in November of a new nylon material failed on its 1995 due to a failure in its old Wicat first test flight last November at Utah More NelNs computer. State University. The balloon exploded The META II system was installed on on the ground during inflation, which The Mars Underground News: one of the two 30-meter antennas at the fortunately prevented the loss of the Life after meteorite ALH84001 Argentine Institute for Radioastronomy, gondola and payload and allowed the and new strategies for continued Mars exploration. located 50 kilometers (30 miles) south university's technical team to examine The NED News: of Buenos Aires. Observations began on the balloon carefully to determine the Since 1983, drilling and seismic October 12, 1990. With funding from the exact cause of the failure. rnissions have confirmed two National Research Council of Argentina, A manufacturing defect was discovered bolide impacts in the western north ' observations of the southern sky (at de­ in the upper seam of the balloon, and the Atlantic Ocean. The story of the clinations between -10 and -90 degrees) balloon manufacturer agreed to provide evolving picture of the Chesapeake and Toms Canyon craters. have been conducted on 80 nearby stars another balloon to be tested in early The Bioastronomy News: that may have solar systems. 1997. The Planetary Society and NASAl A tribute to Carl Sagan and his Southern-sky observations began Ames cosponsored the test. For a play­ impact on bioastronomy. again with the repaired old system on by-play of the test, check the Society's For more information on these December 26, 1996, with installation of Web site: http://planetary.org/tps/. publications, please contact the new system planned for the end of - Louis D. Friedman, Society headquarters; see page 2. 1997. "The incredible efforts of our US Executive Director 19 Questions and AnslNers

When we finally do get to the point of rocks before they had a reasonable I doubt that any funding agency, where we have explored the Moon in probability of turning up a meteorite. such as NASA or the National Science detail, what is the likelihood that we Nevertheless, one such meteorite frag­ Foundation, would back such a high­ will find Earth rocks there just as we ment was found by Hap McSween of risk project. You will probably not find Mars rocks on Earth? the University of Tennessee while he hear about Earth rocks found on the -Gary Gilbert, was examining a lunar soil sample Moon very soon, unless someone Corona, Arizona brought back by the Apollo astronauts. comes up with a clever technique of The millimeter-sized fragment of car­ picking them out of the vast sea of Finding an Earth rock on the Moon is bonaceous chondrite was found on the broken rocks that litter the Moon's possible but very unlikely, even for an rim of a small crater and is probably a entire surface. expert looking for such a rock. Mars remnant of the meteorite that made the -H. J. MELOSH, and Moon rocks are very rare on Earth. crater. However, given the care with University ofArizona There are about 4000 known meteorites, which the Apollo samples were exam­ of which only a dozen are believed to ined, the "one in a million" estimate Why does the heliopause also define have come from Mars or the Moon. is probably not far out of line. the outermost extent of the Sun's Most people, including geologists and Another problem with finding mete­ magnetic field? The solar wind meteoriticists, walk the Earth their orites on the Moon is the lack of an doesn't have anything to do with entire lives without finding a single atmosphere. Meteorites "hard land" on creating the magnetic field, does it? meteorite. Most of the meteoriticists the Moon's surface and so are mostly - James W. Jones, who "discover" new meteorites depend melted and vaporized (with the excep­ Colonial Heights, Virginia on someone from the general public tion of a few small fragments like the to bring in a strange rock they have one mentioned above). Earth's atmo­ No spacecraft has observed the helio­ encountered. About one in 500 such sphere decelerates incoming meteoroids pause region yet. However, current rocks turns out to be a real meteorite. with diameters up to a few tens of theory suggests that the outflowing Meteorites are collected in the high­ meters and drops the slowed stones solar wind and the magnetic field est abundances in places where a solid relatively gently to the surface, where embedded in it should run into and stone is very unusual. Early in this they can be collected more or less pile up against the interstellar plasma century Harvey Nininger collected intact. On the Moon only a small (plus its embedded magnetic field). many meteorites from farmers in the fraction of the back surface of a "hard The heliopause is the boundary that plains states of Kansas and Nebraska, landed" meteorite spalls (breaks or separates these two plasmas (ionized where any stone in the soil was an chips) off during the impact and is gases whose free electrons carry elec­ anomaly. In more recent years, expedi­ thrown out of the crater, along with trical currents coupled to the magnetic tions to Antarctica have turned up a much larger volume of ejecta from field). As new solar-wind plasma con­ meteorites in "blue ice regions," where the Moon's surface. tinually arrives at the heliopause, it the ice flow is forced to the surface Perhaps the best strategy for finding turns and flows parallel to the motion and the wind then erodes away that Earth rocks on the Moon would be to of the interstellar plasma (relative to ice--exposing any rocks embedded look at the ejecta deposits of small the solar system). In this respect our within. (See the January/February craters, searching for fragments of the solar system should resemble a gigantic 1997 issue of Th e Planetary Report). impacting meteoroid. If the occurrence comet, complete with a tail hundreds Again, a stone of any sort is rare on of Earth rocks on the Moon is similar of astronomical units long. the ice and so has a high probability to that of Mars rocks on Earth, you The reason that the Sun's magnetic of being a meteorite. would have to examine about 300 field extends measurably all the way to Unfortunately, the Moon probably craters (and find identifiable fragments the heliopause is that it is dragged out does not have any such stone-free of each projectile!) before there was a there by the solar wind. (Describing regions, so meteorite hunters there reasonable chance of fmding one made the solar wind as "dragging" the Sun's 20 would have to examine literally millions by an Earth rock. magnetic field is only a conceptual crutch, but quantitative physics back in the early 1970s, when the Factinos produces the same result.) By . Project Cyclops study concluded dragging the Sun's magnetic field that Earth's radio "leakage" (that's lines out to the heliopause, the solar what they called it, honest!) would Two new members of our solar system-a wind causes the solar field strength be detectable out to 50 light years near-Earth asteroid and a distant comet making there to be greater than it would (exactly your number) by an alien its only appearance-have been detected by be otherwise. This increased mag­ civilization if it used an antenna scientists from the Jet Propulsion Laboratory. netic field energy at the heliopause 5 kilometers (about 3 miles) in The discoveries, reported on January 10, 1997 comes at the expense of a small diameter. Such an antenna is ex­ by Eleanor Helin and her team, were made fraction of the solar wind's energy travagantly beyond the resources with the Near-Earth Asteroid Tracking (NEAT) of motion. of the Planetary Society, or just system at Mount Haleakala on Maui, Hawaii. With luck and longevity, Voy­ about any other entity on Earth "This asteroid is a member of a rare class agers 1 and 2 should encounter right now. On the other hand, if of asteroids, called Atens, which stay within the heliopause within a decade or we were to transmit, with contem­ Earth's orbit most of their lifetimes," said so and radio back their observa­ porary technology, an intentional Helin of the new body, dubbed 1997 ACll. tions ofthis most rarefied of high­ beacon signal, optimized for the The asteroid is a faint object that measures vacuum phenomena. At that point job of establishing communica­ about 183 meters in diameter. the spacecraft will leave behind the tion, Earth could be seen, with The team also discovered a new comet, last vestiges ofthe solar system. relative ease, by a similar civili­ designated Comet 1997 AI. "This comet has Both will continue to report on the zation out to thousands oflight traveled a long distance, originating in the interstellar plasma and magnetic years. Oort Cloud, far beyond Pluto's orbit," Helin field until onboard power runs out I think your question has anoth­ said. "It has a parabolic orbit, which means about the year 2020. er layer- something like "why - FLOYD HERBERT and should we be looking for signals it will travel through our solar system once ALEX DESSLER, unlike those we are now transmit­ and probably never be seen again. Parabolic University ofArizona ting?" A good and provocative comets do not present their calling cards question. Given that we are pretty before arriving in the inner solar system. Ifthere is now another civilization much guaranteed to be the least They appear without warning." on a planet 50 light years away, advanced civilization trying to -from the Harvard Smithsonian Center for with equipment similar to the communicate (go back a hundred Astrophysics Billion-channel Extraterrestrial years and we've got no radio tele­ Assay (project BETA), would it scopes, computers, or electronics), Galileo captured an image (below) of Jupiter's be able to detect the radio trans­ it's only reasonable to assume that ring system on November 9, 1996. This view missions broadcast from Earth the more advanced civilization shows the west ansa ("loop" or "handle") of in 1946? (i.e., Them) will use effective and Jupiter's main ring with details as small across -Sam Walker, proven beacon signals to bring as 24 kilometers (15 miles). Internal structure Harrogate, Yorkshire, England new members into the galactic is clearly visible here-something Voyager Internet. So the question should images merely hinted at. Variations in the ring's In a word, no. Project BETA (like perhaps be, "Can BETA detect a brightness are caused by the perturbations of just about every other search) isn't beacon of the sort an advanced small satellites. looking for domestic broadcasting civilization, or galactic consortium, Adrastea and Metis (two small satellites not activities of alien civilizations­ might well be sending?" We don't visible in this image) orbit through the outer as nice as that would be-simply know for sure, but we certainly portion of the ring; scientists will determine because it would require resources hope so. their locations relative to these features after far beyond anything we could -PAUL HOROWITZ, further analysis. muster. This was recognized way Harvard University -from JPLINASA

This GaJileo picture 0' Jupiter's ring system reveals details much finer than were possible in Voyager's ring imagllS.

Image: JPLlNASA

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Perli Pelzig was born in Poland in 191 7 but has lived rnost of his life in Germany, Israel, and the United States. In .addition to painting, he has produced works in various media from scu lpture to stain ed glass for universities, synagogues, ch urches, and other public buildings.

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