Jet Propulsion Laboratory UNIVERSE Pasadena, California - Vol. 26, No. 26 - December 27, 1996 __________________________________________________________________ Galileo team hears 'voice' of Ganymede By MARY BETH MURRILL Jupiter's big moon Ganymede is not only the size of a planet-it sounds like one too, as heard in audio recordings made from data returned by NASA's Galileo spacecraft released Dec. 12. Characterized by a soaring whistle and hissing static, Ganymede's song reveals that the solar system's largest moon is also the only one known to possess a planet-like, self-generated magnetic cocoon called a magnetosphere, which shields the moon from the magnetic influence of its giant parent body, Jupiter. Published in the scientific journal Nature earlier this month, these new Galileo findings and other measurements from several Galileo sensors were presented Dec. 13 in a news briefing held at JPL. Taken together, scientists say the new Ganymede findings are painting a portrait of a body that from the inside out closely resembles a planet like Earth rather than other moons in the solar system. "The data we get back is in the form of a spectrogram, and reading it is kind of like looking at a musical score," said Dr. Donald Gurnett, University of Iowa physicist and principal investigator on Galileo's plasma wave instrument. It was his experiment that first detected the telltale signals of a magnetosphere during the spacecraft's close flybys of that moon on June 27 and Sept. 6. Gurnett said the unique pattern of frequencies his instrument detected is characteristic of a magnetosphere and closely matches his previous studies of the magnetospheres of Earth, Saturn and Jupiter. "The instant I saw the spectrogram, I could tell we had passed through a magnetosphere at Ganymede," Gurnett said. Describing the electromagnetic wave activity that his experiment detected at Ganymede, Gurnett said the approach to the large moon was relatively quiet, "until all of a sudden, there's a big burst of noise that signals the entry into Ganymede's magnetosphere. Then, for about 50 minutes, we detected the kinds of noises that are typical of a passage through a magnetosphere. As we exited the magnetosphere, there was another big burst of noise." Gurnett checked with Dr. Margaret Kivelson of UCLA, principal investigator for the magnetometer experiment on the spacecraft. Kivelson quickly confirmed the detection of a large increase in magnetic field strength near Ganymede. Related data from the two close flybys have confirmed that Ganymede has a magnetic field of its own. Using extremely precise data from tracking the spacecraft, investigators on Galileo's celestial mechanics team also have been able to confirm that Ganymede's interior is differentiated, probably having a three-layer structure. "These data show clearly that Ganymede has differentiated into a core and mantle which is, in turn, enclosed by an ice shell," said JPL planetary scientist Dr. John Anderson, team leader on the Galileo radio science experiment. "Combined with the discovery of an intrinsic magnetic field, our gravity results indicate that Ganymede has a metallic core about 400 to 1,300 kilometers (250 to 800 miles) in," Anderson said. "This is surrounded by a rocky silicate mantle which is, in turn, enclosed by an ice shell about 800 kilometers (500 miles) thick. Depending on whether the core is pure iron or an alloy of iron and iron sulfide, it could account for as little as 1.4 percent or as much as one-third of the total mass of Ganymede." This differentiated structure is the most likely cause of Ganymede's newly discovered magnetic field which, in turn, gives rise to the magnetosphere, reported UCLA geophysicist Dr. Gerald Schubert, an interdisciplinary investigator on Galileo's science team. Scientists suspect Ganymede's magnetic field is generated the same way as Earth's, through the dynamo action of the fluid mantle rotating above a metallic core. The only other solid bodies in the solar system known to have magnetic fields are Mercury, Earth and possibly Jupiter's volcanic moon Io. "At Ganymede, the magnetic field is strong enough to carve out a magnetosphere with clearly defined boundaries within Jupiter's magnetosphere, making it the only 'magnetosphere within a magnetosphere' known in the solar system," Kivelson said. The strong magnetic characteristics of Ganymede, in combination with its residence within Jupiter's powerful magnetosphere, makes the Jovian environment even more intriguing, said Galileo Project Scientist Dr. Torrence Johnson. "The physics taking place within Jupiter's magnetosphere are of great interest to scientists attempting to understand the complex interplay of magnetic forces and matter throughout the universe," he said. Data from the plasma wave instrument can be heard and seen on the Galileo home page at http://www.jpl.nasa.gov/galileo. Newly received Galileo images of Jupiter's moon Callisto and one of Europa also were released at the briefing. Scientists were surprised by the lack of small craters visible in the images. Some small craters appear to have been softened or modified by downslope movement of debris, revealing ice-rich surfaces. Galileo's next moon encounter occurred Dec. 18-19, when the spacecraft made its first close approach to Europa, the moon thought to harbor a liquid ocean beneath its icy surface. Results from that flyby will be radioed to Earth starting in the last half of December and continuing through early February 1997. The Europa image received from the spacecraft in early December shows the cracked surface of this moon in greater detail than it has been seen before. The new image shows an area 238 by 225 kilometers (150 by 140 miles) that has been highly disrupted by fractures and ridges. Arizona State University planetary scientist Kelly Bender of Galileo's imaging team said that symmetric ridges in the dark bands suggest that Europa's surface crust was separated and filled with darker material, somewhat analogous to spreading centers in the ocean basins of Earth. Although some impact craters are visible, their general absence indicates a youthful surface, she said. The youngest ridges, such as the two features that cross the center of the picture, have central fractures, aligned knobs and irregular dark patches. These and other features could indicate cryovolcanism, or processes related to the eruption of ice and gases. ### __________________________________________________________________ Northridge quake hasn't stopped; hills have risen By MARY HARDIN JPL earthquake researchers measuring the movement of the Earth's surface with the Global Positioning System (GPS) have concluded that the Northridge earthquake has continued in a "quiet" way and the Granada Hills have risen about 16 centimeters (about 6 inches) since that first jolt in January 1994. Scientists from JPL presented their findings in mid-December at the annual fall meeting of the American Geophysical Union in San Francisco. "The Northridge quake occurred on a thrust fault that did not break all the way to the surface. However, the sedimentary layers of rock, in the top five kilometers located just below the surface near the epicenter, have continued to move in a fluid-like manner-sort of like honey flowing off a spoon-since the earthquake," said Dr. Gregory Lyzenga, a JPL geophysicist and professor at Harvey Mudd College in Claremont. "The amount of motion that happened because of this 'stealth' earthquake is equivalent to the displacement that would accompany a magnitude 6.0 earthquake." Lyzenga and his JPL colleague Dr. Andrea Donnellan studied data from about a dozen GPS receivers that continuously measure the constant, yet nearly physically imperceptible, movements of earthquake faults throughout Southern California. These temporary GPS sites were part of a preliminary earthquake study that helped lead to a large effort called the Southern California Integrated GPS Network (SCIGN). The network uses an array of permanent GPS receivers placed throughout the region. GPS uses data transmitted from a constellation of 24 Earth-orbiting satellites that are jointly operated by the departments of Defense and Transportation. The satellites are arranged so that several of them are "visible" from any point on the surface of the Earth at any time. Scientists at JPL can determine the position of a user with a GPS receiver to better than 1 centimeter (0.4 inches) per day by correlating signals from the satellites and knowing the satellite orbital locations very accurately. "It is not clear yet if this continued post-Northridge "after-slip" represents a loss of stress along a fault or if it is a transfer of stress to other areas," Lyzenga said. "Our GPS processing techniques are now better refined, making it easier to resolve vertical as well as horizontal movements of the Earth's surface." What is clear is that the force of the after-slip has added about 16 centimeters (about 6 inches) to the Granada Hills since the earthquake. "While similar post-seismic movements have been seen after earthquakes in other regions, this observation is significant because it highlights the difficulty of fully accounting for all of the strain that can potentially lead to earthquakes," Lyzenga added. "If we hope to make realistic assessments of earthquake potential in different parts of the Los Angeles basin, we need to understand the processes and amounts of quiet movement, as well as the more obvious shifts that occur immediately during seismic events." In a related observation, researchers studying GPS measurements from a single site located in the foothills behind JPL have seen the rate of motion at that site change significantly since the Northridge quake. "This extra motion cannot be easily explained by means of additional slip on the fault which ruptured during the Northridge earthquake, suggesting the possibility of slip on a second fault closer to JPL," said Dr. Michael Heflin, a JPL geophysicist. "The extra motion may represent a significant release of strain energy which is occurring without earthquakes. If such events turn out to be common, the overall earthquake hazard may need to be reevaluated." The ongoing measurements of the new and growing SCIGN array will help clarify the "earthquake budget," or the amount of strain accumulation that has built up in Southern California. If the observations show that significant strain energy is released quietly, then less total energy is left to be released and we may experience fewer damaging earthquakes, Heflin added. ### __________________________________________________________________ Sagan played key roles in JPL missions, friends recall Dr. Carl Sagan and his long history of contributions to space missions conducted by JPL were remembered by his scientific colleagues following his death Dec. 20. Sagan had key roles in shaping the course of exploration of the planets with robotic spacecraft since the 1960s to the present. At the time of his death, he was an interdisciplinary scientist on JPL's Galileo mission to Jupiter. JPL Director Dr. Edward Stone, who also served as project scientist on the Voyager mission, commented: "The world's science community, and the field of planetary exploration in particular, have lost one of its most gifted minds and eloquent voices in the passing of Dr. Carl Sagan. As a team member on various planetary missions, Carl repeatedly demonstrated a special capability to understand the significance of a finding and place it in context. His contributions to the Voyager program, over some 20 years, were significant in making it the very successful exploration of the outer planets that it was. I personally shall miss his wise counsel. "The entire JPL staff joins me in mourning his loss and extending our deepest sympathies to the Sagan family. " Dr. Torrence Johnson, Galileo Project Scientist, who also worked with Sagan as a fellow member of the science team on the Voyager missions to Jupiter, Saturn, Uranus and Neptune, recalled: "Carl was one of the greatest intellects behind the genesis of space exploration generally and specifically the Galileo mission. He was part of the original group that got together to promote the mission to NASA and he served as an interdisciplinary scientists on the mission team from the beginning. He was a great human being who shared with everyone his excitement about the exploration of the universe." Galileo Project Manager Bill O'Neil expressed the team's grief at Sagan's passing: "The Galileo mission team is heartbroken with the loss of Carl Sagan. Carl was one of our most esteemed interdisciplinary scientists on the Galileo Project Science Group. But more than that, Carl was a wonderful colleague and dear friend to us all. Carl is very well known for his tremendous success in engaging the public in space exploration. Not so well known is that Carl was extremely effective in helping save Galileo from the budget ax many times in the early years of the project. We are greatly indebted to Carl for his support and inspiration through the years." Dr. Carolyn Porco of the University of Arizona heads the imaging team for JPL's Cassini mission to Saturn. She attributes much of her success in science to early mentoring she received from Sagan: "Of all the people I have met in the course of my scientific career, no one was more gracious, understanding, respectful and encouraging towards me than Carl. From my very first professional presentation at the age of 21, to my current position as the Cassini imaging team leader, Carl was there, always, with a kind, gentle word of support. I believe that he cared for people, genuinely, in that special way that distinguishes great humanitarian leaders. And I believe that underlying his life's work was a bedrock faith in the fragile dignity and goodness of all humankind. "His passing is a heartbreaking loss-for his family, for the community of scientists that he walked among, and for the world. We who remain on Earth have lost our guardian angel. He is part of the cosmos now." ### __________________________________________________________________ Donnellan, Stofan honored by White House By MARY HARDIN Two JPL scientists are among six NASA recipients of a new presidential award that recognizes outstanding young scientists who are beginning their independent research careers. Dr. Andrea Donnellan and Dr. Ellen Stofan received the Presidential Early Career Award for Scientists and Engineers at a Dec. 16 ceremony in Washington, D.C. The award is the highest honor bestowed by the U.S. government on young professionals whose talents and potential are so great that they are expected to be leaders in the frontiers of science and engineering in the 21st century. The recipients received funding to support their research over the next five years. They will also serve as advisors to the president on emerging and developing trends and discoveries in their fields. Donnellan was recognized for her work using the Global Positioning System (GPS) satellite technology to study earthquakes and the corresponding movements of the Earth's crust. She is currently a team member on the Southern California Integrated GPS Network (SCIGN), an array of 250 GPS receivers that will continuously measure the constant, but nearly physically imperceptible movements of earthquake faults throughout Southern California. The network will help scientists forecast future earthquake hazards in the greater Los Angeles area. Donnellan is also a visiting associate at the Seismological Laboratory at Caltech. She has conducted field studies in California in the region of the Northridge earthquake, the Ventura basin and on the San Andreas fault. She has also carried out field work in Antarctica on the West Antarctic Ice Streams, on the Altiplano of Bolivia and on Variegated Glacier in Alaska. A resident of Altadena, the 32-year-old Donnellan was raised in Arlington Heights, Ill. She received her doctorate in geophysics in 1991 and her master's degree in 1988 from Caltech. She graduated from Ohio State University in 1988 with a bachelor of science degree in geology and mathematics. Stofan is a planetary geologist who received the award for her geologic mapping studies of Venus, using data from JPL's Magellan spacecraft. Stofan was the deputy project scientist for the Magellan mission. She assisted in the interpretation of Magellan radar data, helped to plan the science analysis and provided science input to the Magellan mission operations teams. Stofan has been on sabbatical in London for the past 15 months. She will return to JPL after the first of the year to continue her work as program scientist of the New Millennium project. Prior to taking that position, Stofan was the experiment scientist for the Spaceborne Imaging Radar C/X-band Imaging Radar (SIR-C/X-SAR) project. An Ohio native, Stofan, 35, received her master of science and doctorate degrees from Brown University, Providence, R.I. She graduated from William & Mary College, Williamsburg, Va. in 1983 with a degree in geology and art history. Stofan and her husband Tim Dunn, and their children, Ryan, Emily and Sarah, live in Pasadena. In addition to the NASA recipients, other awardees were from the departments of Agriculture, Commerce, Defense, Energy, Health and Human Services and Veteran Affairs, as well as the Environmental Protection Agency and the National Science Foundation. ### __________________________________________________________________ Space Coast childhood led engineer to JPL career By JUDITH McGAVIN, Advisory Council for Women As fate would have it, Linda Robeck's career in space science may have been determined when she was just a child É or perhaps even sooner. Robeck, who works in Section 352, had a chance to reminisce about those early days recently, when she worked at Kennedy Space Center to help prepare Mars Pathfinder for its launch earlier this month. She found herself back in her old stomping grounds. From her birthplace of nearby Vero Beach, Fla., her family used to watch NASA launches on television, then run out into the yard to watch the rockets clear the trees. Then, when she was still a baby, Robeck's family moved to the Boston area, in a house at the end of the runway at Hanscom Air Force Base. An inspiring moment came when she was about 6, she recalled. Her father took her out into the yard one evening and pointed out a star that moved slowly across the sky against the dark field of stars. It was an Apollo spacecraft, and her dad told her there were men in that star. Her mind just lit up, and a permanent fascination with space and science ensued. Now a nine-year JPL veteran, Robeck worked on a mechanical engineering team at KSC that was in charge of assembling Pathfinder's lander. She worked with cognizant engineers and teams responsible for the spacecraft's rover, camera, wind sensors and other instruments, ensuring that everything came together and worked according to schedule. She joined the Pathfinder project in mid-1995 as a member of the assembly test and launch operations (ATLO) team, and prior to that served as JPL's metric conversion task manager, helping to heighten awareness to NASA's mandate to its centers to implement metrics. As far back as she can recall, Robeck was always interested in the way things work, rather than how they look. "I do remember, as a small child, peering into the toaster to see how white bread became brown toast," she said. "I was also very interested in finding out why the heaters used to 'bang' in the winters." Later, she spent hours in her family's dirt driveway performing little erosion experiments, and was especially interested in watching to see how plants grew. Robeck also conducted scientific experiments in "fluid dynamics." Her family had a pump to keep water out of the basement. The water flowed from a tube at the top of the driveway. "I spent many hours experimenting with different sizes and shapes of dams, using a variety of building materials, such as dry dirt, wet dirt, grass clippings, sticks, rocks and various combinations." Her family encouraged this method of entertainment for quite some time. But it was more than entertainment. Fortunately, on the serious side, Robeck's parents both influenced an atmosphere of learning and exploration for her and her two older sisters and brother. She and her sisters, however, had to overcome what she termed her father's "old world ideas" about women in the workplace. She says her dad was a firm believer that women could do whatever they wanted to-as long as they cooked, cleaned and took care of the kids, so her primary tasks while growing up included cleaning and preparing meals. But she also had chances to help out in the garage, bleeding brake lines or resetting the clutch. Yard work and snow shoveling were also part of her household assignments. Her father even encouraged her to learn how to change tires before she applied for her driver's license. "He expected us to be well-educated, but was surprised when I went into engineering," Robeck said. Each of her siblings has now earned master's degrees in science or engineering, which pleased her dad to no end. "He loved it to pieces, the fact that all of his children became professionals," she noted. "He especially loved to brag about me and his other daughters." Robeck's mother, Gisela, was no less inspirational. After 20 years of homemaking, her mom went back to school, earning a bachelor's degree in computer science from Northeastern University in Boston, followed by a master's degree in finance from Boston College. She then worked her way up to the equivalent of a division manager for a major life insurance company before retiring in 1992. But that is just part of her mother's story. Gisela survived World War II by escaping across the Russian border from East Germany into West Germany one night and ended up supporting herself and a younger brother and sister until she emigrated to the United States in 1952. Following her parents' divorce when she was 11, Robeck lived with her mother. She said she kept up her interest in science by learning to do preventative maintenance on household appliances. Although Robeck was always enamored of the space program, she said she had never thought about it as a career until a poignant moment in her high school physics class, when she used a calculator to figure out the orbit of Jupiter. "'Wow!,'" she thought. "A pimply-faced kid with a pencil and a few equations can figure out the motions of the planets!" Shortly thereafter, she applied to MIT to study physics, eventually earning a bachelor's degree in aeronautics and astronomy, followed by a master's in science from Stanford. Following the Space Shuttle Challenger disaster in early 1986, Robeck found that NASA wasn't doing much hiring, but a friend informed her of an opening at JPL the following year. She then joined the Galileo project in mid-1987, working on the integration of the attitude control system. Robeck said the most interesting work she's done at JPL was the ATLO work for Mars Pathfinder. "It was the hardest thing I've ever had to do," she said. "We had to start from nothing and build an autonomous spacecraft that will land on another planet. We had to learn everything about how each instrument and mechanism worked, how to put it together and how to take care of it. We were the final caretakers of that hardware; hundreds of people were counting on us to bring the whole thing to a final, integrated, complete spacecraft. "We worked extremely long hours, nights and weekends, fixing problems no one had seen until the last minute, making things fit, and all the while handling all of the constraints that keep us from causing a biological contamination of Mars. It was really hard work, but very, very rewarding." However, her most memorable moment was when the Pathfinder ATLO crew threw a surprise birthday party for her last January. She had no idea anything was in the works. "That was so nice, I wanted to cry," she recalled. Now that Pathfinder is safely on its way to Mars, Robeck works with the Critical Dynamics in Microgravity (DYNAMX) Preproject, a space science experiment scheduled for a space shuttle flight in 2001. The experiment will investigate the changing properties of helium at extremely cold temperatures. Her work involves cryovalve calibrations needed for flight designs. Robeck hopes to one day become a systems engineer at JPL. Even though systems engineers were formally named only last year, Robeck noted that in her experience, there has always been an informal network of mentors or guides on Lab. "There have been so many changes in the 10 years I've worked here," she said. "When I look back, there's always been a couple of people in each division that others could talk to for advice." In her free time, Robeck is a voracious reader. Spurred by hearing the short story "Arena" (later adapted as a story for the original "Star Trek") at summer camp at age 9, she tumbled headlong into a love affair with science fiction, which continues to this day. Because Pathfinder took up so much of her time this year, Robeck fell short of her goal of reading 100 books a year, reading "only" 30 so far. Her tastes include current popular fiction, non-fiction, and the classics. She also likes to unwind by growing flowers and vegetables in her garden. The most rewarding milestone in Robeck's life was buying a home. "It is hard enough for anyone to buy a home these days, but especially for a woman living alone, with no help from anyone." She currently shares her home with her cat, but that will soon change, as she is engaged to be married to Don Fuhrman, a 10-year JPL veteran. Fuhrman is the system architect for JPL's Product Data Management Services (PDMS), which is a suite of configuration management services, data management services, data distribution services, and technical/engineering information storage and retrieval for the Lab. ### __________________________________________________________________ News briefs Dr. Henry Garrett, lead technologist for the Office of Engineering and Mission Assurance, has co-authored a college-level textbook based partly on his JPL work of specifying and defining environmental requirements for Lab missions. The book, called "SpacecraftÐ Environment Interactions," was co-authored by MIT professor Daniel Hastings and is used in one of his courses there. Garrett said the book is in widespread use at universities throughout the country with spacecraft design courses. Garrett added that the book is available for loan at the JPL Library and for sale at the Caltech bookstore, staff/faculty section. For more information, call him at ext. 4-2644. ### The JPL Genealogy Club has announced that its regular membership meetings have been changed to the first Tuesday of the month. The next meeting will be held on Jan. 7 at noon in Bldg 301-169. For more information, see the Genealogy Club home page at http://www.jplerc.org/ genealog/. Genealogy Club president Jay Holladay recommends a new PBS series about family history beginning in January. The show will air on KCET, Channel 28 beginning on Sunday, Jan. 5, at 6:30 p.m. The show's 10 30-minute segments will air on consecutive Sunday evenings at the same time. Episodes will cover such topics as: getting started, gathering family stories, census and military records, African American research and high-tech help. Additional information about the series is available at http://www.kbyu. byu.edu/ ancestors/. ### __________________________________________________________________ X-33 manager discusses program Gene Austin, manager of NASA's X-33 program, presented an overview of the program's demonstration vehicle to a von K‡rm‡n Auditorium audience Dec. 13. The demonstration vehicle, according to JPL Defense Space Technology Manager Ken Russ, is a steppingstone to NASA's Reusable Launch Vehicle, intended to lead to cheaper and more frequent space flights. Russ said that Austin's briefing was a follow-up to Vice President Al Gore's announcement at JPL in July that Lockheed Martin's Skunk Works facility in Palmdale had won the competitive bid to build the X-33 test vehicle. "The X-33 demonstration vehicle is scheduled to first fly early in 1999, when it will complete 15 flights," Russ said. "The economic feasibility and performance reliability of the RLV space plane is to be established by the X-33 program." Russ also will manage two support tasks that JPL will contribute to the RLV. One, called vehicle health management, "will ensure incorporation of proper status sensors on the RLV that will make it as safe as present-day airplanes that fly over land," he said. The other task, Russ added, is an avionics flight experiment that "will demonstrate the capability to manage large and diverse quantities of data, which will allow operational costs to be greatly reduced." A videotape of Austin's speech is available for loan from the Audiovisual Services Office. ### __________________________________________________________________ Universe Editor, Mark Whalen Photos, JPL Photo Lab Universe is published every other Friday by the Public Affairs Office of the Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109.