MARSBUGS: The Electronic Astrobiology Newsletter Volume 6, Number 18, 19 July 1999. Editors: Dr. David J. Thomas, Biology and Chemistry Division, Lyon College, Batesville, AR 72503-2317, USA. Marsbugs@aol.com or dthomas@lyon.edu Dr. Julian A. Hiscox, School of Animal and Microbial Sciences, University of Reading, Reading, RG6 6AJ, United Kingdom. J.A.Hiscox@reading.ac.uk Marsbugs is published on a weekly to quarterly basis as warranted by the number of articles and announcements. Copyright of this compilation exists with the editors, except for specific articles, in which instance copyright exists with the author/authors. While we cannot copyright our mailing list, our readers would appreciate it if others would not send unsolicited e-mail using the Marsbugs mailing list. The editors do not condone "spamming" of our subscribers. Persons who have information that may be of interest to subscribers of Marsbugs should send that information to the editors. E-mail subscriptions are free, and may be obtained by contacting either of the editors. Article contributions are welcome, and should be submitted to either of the two editors. Contributions should include a short biographical statement about the author(s) along with the author(s)' correspondence address. Subscribers are advised to make appropriate inquiries before joining societies, ordering goods etc. Back issues and Adobe Acrobat PDF files suitable for printing may be obtained via anonymous FTP at ftp.uidaho.edu/pub/mmbb/marsbugs or at the official Marsbugs web page at http://members.aol.com/marsbugs/marsbugs.html. The purpose of this newsletter is to provide a channel of information for scientists, educators and other persons interested in exobiology and related fields. This newsletter is not intended to replace peer-reviewed journals, but to supplement them. We, the editors, envision Marsbugs as a medium in which people can informally present ideas for investigation, questions about exobiology, and announcements of upcoming events. Astrobiology is still a relatively young field, and new ideas may come out of the most unexpected places. Subjects may include, but are not limited to: exobiology and astrobiology (life on other planets), the search for extraterrestrial intelligence (SETI), ecopoeisis and terraformation, Earth from space, planetary biology, primordial evolution, space physiology, biological life support systems, and human habitation of space and other planets. ---------------------------------------------------------------- CONTENTS 1) "DEEP IMPACT" IN CHESAPEAKE BAY USGS release 2) SPACE COLLISION HELPED CREATE CHESAPEAKE BAY, LEAVES DRINKING WATER SALTY By Robert Roy Britt 3) ANOTHER ASTEROID THREAT DEFUSED By Alan Boyle 4) SAHARA'S ABRUPT DESERTIFICATION STARTED BY CHANGES IN EARTH'S ORBIT, ACCELERATED BY ATMOSPHERIC AND VEGETATION FEEDBACKS American Geophysical Union release 99-20 5) EVERY ASTRONAUT SHOULD HAVE ONE By Catherine Zandonella 6) BIS LIFE ON MARS PROCEEDINGS By Julian Hiscox 7) CASSINI MISSION STATUS REPORT JPL release 8) GALILEO--COUNTDOWN TO CALLISTO By Ron Baalke 9) TAKING THE SCENIC ROUTE TO IO Marshall Space Flight Center release 10) THIS WEEK ON GALILEO JPL releases 11) TODAY ON GALILEO JPL releases ---------------------------------------------------------------- "DEEP IMPACT" IN CHESAPEAKE BAY USGS release 6 July 1999 No, not another meteor disaster movie, but something left a big impression in the Chesapeake Bay. "About 35 million years ago a huge rock or chunk of ice slammed into the Atlantic Ocean and blasted a 56-mile-wide hole in the shallow ocean floor near what is now the mouth of the Chesapeake Bay," David Powars, hydrologist with the U.S. Geological Survey (USGS) said. "The force of the impact ejected huge amounts of debris into the atmosphere and spawned a train of gigantic tsunamis that probably reached as far as the Blue Ridge Mountains. This impact left behind a crater that is now buried under 400 to 1,200 feet of sand, silt, and clay." Scientists with the USGS and the Virginia Department of Environmental Quality have recently discovered the Chesapeake Bay impact crater. The USGS, in cooperation with the Hampton Roads Planning District Commission, has just released the first of a series of planned reports describing the effects of the impact crater on the geology and hydrogeology in the region. "Ongoing analysis of this impact crater will yield a wealth of information," Powars said. "It's the largest crater discovered so far in the United States, and it's one of only a few oceanic impact craters that have been documented worldwide. The Chesapeake Bay impact crater is shallower and more accessible than the much larger and older one off the coast of Mexico that most scientists believe led to the extinction of the dinosaurs." The discovery of the Chesapeake Bay impact crater helps explain a number of unusual features that have been noted in the region, including salty ground water, earthquakes around the crater's perimeter, and an unusual rate of sea-level rise. "The object from outer space that hit the Earth millions of years ago appears to be responsible for the salty ground water that we find at depth over a large area in the bay region," Powars explained. Virginia's "inland saltwater wedge" is a well-known but previously unexplained phenomenon. The impact of the comet or meteorite deformed and broke up the "layer cake" stack of aquifers and confining units. The outer rim of the crater seems to coincide with the boundary separating salty ground water inside the outer rim from fresher, lower salinity water outside the outer rim. The report documents the location and nature of the outer rim. This information can be used to determine where fresh ground water is likely to be found. The report presents a reinterpretation of the lower York-James Peninsula geologic framework and is the first step in understanding the ground-water flow system. "In other words," said Powars, "first you have to describe the container and the material holding the water before you can begin to describe how the water flows. The next step will be revising existing computer ground-water flow models." The computer models are used to guide the management of Virginia's ground-water resources, such as the permitting of large ground- water withdrawals. Copies of U.S. Geological Survey Professional Paper 1612 "The Effects of the Chesapeake Bay Impact Crater on the Geological Framework and Correlation of Hydrogeologic Units of the Lower York-James Peninsula, Virginia" by David S. Powars and T. Scott Bruce, are available for viewing at university, state, and government depository libraries and at the USGS Virginia District office, 1730 East Parham Road, Richmond, VA 23228 (804) 261-2600. Copies may be purchased from the USGS, Branch of Information Services, Box 25286, Federal Center, Denver, CO 80225. More information about water-resource programs in Virginia may be found at http://va.water.usgs.gov/. As the nation's largest water, earth and biological science and civilian mapping agency, the USGS works in cooperation with more than 2000 organizations across the country to provide reliable, impartial, scientific information to resource managers, planners, and other customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, to contribute to the conservation and the sound economic and physical development of the nation's natural resources, and to enhance the quality of life by monitoring water, biological, energy, and mineral resources. ---------------------------------------------------------------- SPACE COLLISION HELPED CREATE CHESAPEAKE BAY, LEAVES DRINKING WATER SALTY By Robert Roy Britt 7 July 1999 A huge object from space slammed into Earth 35 million years ago, carving the largest crater ever found in the United States, researchers said today. The 56-mile-wide crater was gutted from what is now the mouth of Chesapeake Bay in a cataclysmic collision that kicked a cloud of debris high into the atmosphere and spawned devastating tsunami waves up to 2,000 feet high. The full story may be obtained at http://explorezone.com/archives/99_07/07_chesapeake_impact.htm ---------------------------------------------------------------- ANOTHER ASTEROID THREAT DEFUSED By Alan Boyle, MSNBC 13 July 1999 Yet another asteroid threat has been knocked down at last, thanks to a re-examination of 44-year-old images made by the Palomar Observatory. Astronomers had said there was more than a 1-in-a-million chance that Asteroid 1999 AN10 could collide with Earth in the middle of the next century. But a review of the Palomar images provided enough information about the asteroid's path to eliminate even that chance... at least through 2076. The full story may be obtained at http://www.msnbc.com/news/272798.asp ---------------------------------------------------------------- SAHARA'S ABRUPT DESERTIFICATION STARTED BY CHANGES IN EARTH'S ORBIT, ACCELERATED BY ATMOSPHERIC AND VEGETATION FEEDBACKS American Geophysical Union release 99-20 7 July 1999 One of the most striking climate changes of the past 11,000 years caused the abrupt desertification of the Saharan and Arabia regions midway through that period. The resulting loss of the Sahara to agricultural pursuits may be an important reason that civilizations were founded along the valleys of the Nile, the Tigris, and the Euphrates. German scientists, employing a new climate system model, have concluded that this desertification was initiated by subtle changes in the Earth's orbit and strongly amplified by resulting atmospheric and vegetation feedback in the subtropics. The timing of this transition was, they report, mainly governed by a global interplay among atmosphere, ocean, sea ice, and vegetation. Their research is published in the July 15 issue of Geophysical Research Letters. The researchers, headed by Martin Claussen of the Potsdam- Institut fuer Klimafolgenforschung (Potsdam Institute for Climate Impact Research) employed a model of intermediate complexity to analyze climate feedback during the past several thousand years of the current, or Holocene, era. Called CLIMBER-2 (for CLIMate and BiosphERe, version 2.1), the model led to the conclusion that the desertification of North Africa began abruptly 5,440 years ago (+/- 30 years). Before that time, annual grasses and low shrubs, as evidenced by fossilized pollen covered the Sahara. The transition to today's arid climate was not gradual, but occurred in two specific episodes. The first, which was less severe, occurred between 6,700 and 5,500 years ago. The second, which was brutal, lasted from 4,000 to 3,600 years ago. Summer temperatures increased sharply and precipitation decreased, according to carbon-14 dating. This event devastated ancient civilizations and their socio-economic systems. Changes in the Earth’s orbit and the tilt of Earth’s axis initiated the change from the mid-Holocene climate to that of today. Some 9,000 years ago, Earth's tilt was 24.14 degrees, as compared with the current 23.45 degrees, and perihelion, the point in the Earth's orbit that is closest to the Sun, occurred at the end of July, as compared with early January now. At that time, the Northern Hemisphere received more summer sunlight, which amplified the African and Indian summer monsoon. The changes in Earth's orbit occurred gradually, however, whereas the evolution of North Africa's climate and vegetation were abrupt. Claussen and his colleagues believe that various feedback mechanisms within Earth's climate system amplified and modified the effects touched off by the orbital changes. By modeling the impact of climate, oceans, and vegetation both separately and in various combinations, the researchers concluded that oceans played only a minor role in the Sahara's desertification. The CLIMBER-2 models showed that feedback within the climate and vegetation systems were the major cause of Saharan desertification, building rapidly upon the effects of the initial orbital changes. The model suggests that land use practices of humans who lived in and cultivated the Sahara, were not significant causes of the desertification. Further investigation is necessary, the researchers say, to determine more precisely the specific effects of latitude and oceanic feedback, as compared with biospheric feedback, on the timing of the event. Notes for science writers and science public information officers 1. You may receive a copy of this paper, Martin Claussen, Claudia Kubatzki, Victor Brovkin, Andrey Ganapolski, Philipp Hoelzmann, Hans-Joachim Pachur, "Simulation of an abrupt change in Saharan vegetation in the mid-Holocene," by sending an email to Harvey Leifert (hleifert@agu.org). If you did not receive this press release directly from AGU, please include your name, name of your publication or organization, and your phone and fax numbers. 2. For further information on the science in this paper, you may contact Professor Dr. Martin Claussen, (claussen@pik- potsdam.de), phone +49 (0) 331 288 2522, or one of the co- authors, whose postal and email addresses will be found at the end of the paper. 3. This press release and the paper to which it refers are not under embargo. ---------------------------------------------------------------- EVERY ASTRONAUT SHOULD HAVE ONE By Catherine Zandonella From the New Scientist 14 July 1999 Remember the floating sparring partner that darted about helping Luke Skywalker refine his lightsabre skills in Star Wars? Well, NASA is busy creating similar robots for its astronauts. Called personal satellite assistants, or PSAs, the tennis-ball-sized robotic helpers will float around spacecraft monitoring oxygen levels, taking snapshots and even fixing minor problems. A roving PSA will be able to go where people can't. For example, astronauts could send it to investigate alarms. "When a fire broke out on the Mir space station," says the PSA project leader Yuri Gawdiak, "it would have been nice to have a PSA to send in to the area to see what was going on." Suspended in microgravity, a PSA will need only tiny fans to move about. It will use range-finding sensors to detect objects--such as astronauts--that get in its way. The battery- powered device will be armed with sensors to detect changes in gas levels, temperature and atmospheric pressure. Designed to work without human supervision, the PSA will communicate with the spacecraft's computers via a wireless network, shifting tougher tasks to the ship's computers to save power. It should also respond to human voice commands or be controlled using a hand-held remote control device, or even by crews on the ground. Besides its monitoring duties, the PSA will serve as a communication port, equipped with microphones and video conferencing capabilities. It will act as a stand-in for scientists who send experiments up into space. Through the PSA, Earthbound researchers could watch procedures being carried out and communicate in real time with the astronauts. "The PSA will allow scientists to interact naturally with the crew," says Gawdiak. "It's an exciting project that has great potential to enable the human exploration of space," said Ken Ford, head of the information technology unit at NASA's Ames Research Center in California. He introduced the PSA concept last week at a Silicon Valley conference on data fusion--which examined the integration of data from multiple sources into single, more manageable streams. The array of sensors used by the PSA will need just such a system to allow the device to make sense of the space it inhabits. NASA scientists say it will be at least two years before the PSA is ready for use on the space shuttle or the International Space Station. "One of the major challenges of a device like this," says aerospace expert Jonathan How of Stanford University, "is how to keep the thing from running into people or doors." Another challenge is keeping its size down. "Small sensors tend to drift, that is, they lose their accuracy over time," he says. The NASA team is now working on collision control software for the device, says Gawdiak. As for its size, Gawdiak says the team is working with the Jet Propulsion Laboratory in California to keep the unit's volume down--while keeping its productivity up. ---------------------------------------------------------------- BIS LIFE ON MARS PROCEEDINGS By Julian Hiscox 14 July 1999 Last year the British Interplanetary Society hosted the first UK symposium to deal with the search for life on Mars. The symposium was also part sponsored by the Planetary Society. The symposium focused on three aspects of Mars exploration; what extinct or extant life might be found on Mars, how this can be detected, and some of the technologies being developed that will reduce mission costs. A conference proceedings volume was published, containing papers not only by the symposium speakers but also by external authors who are experts in their respective fields. Readers of Marsbugs might be interested in these proceedings so content and contact details are shown below. The Search for Life on Mars Editor: Julian A. Hiscox. Published by the British Interplanetary Society (bis.bis@virgin.net). (112 pages illustrated throughout). Contents Life on Mars--A historical perspective. Richard L. S. Taylor, Probability Research Group, UK. The origin and evolution of life on Earth and its possible relevance to Mars. Julian A. Hiscox, University of Reading, UK. On the inevitable emergence of life on Mars. Michael J. Russell and Allan J. Hall, Scottish Universities Research and Reactor Centre and University of Glasgow, UK. Life in extreme thermal environments: Implications for exobiology. Don A. Cowan, University College London, UK. Antarctica as a model for ancient Mars. David D. Wynn-Williams, British Antarctic Survey, UK. Implementing a strategy to explore for ancient Martian life. Jack Farmer, Arizona State University, USA. Artesian basins on Mars: Implications for settlement, life search and terraforming. Martyn J. Fogg, Probability Research Group, UK. Atmospheric change and life on Mars. B. Lee Lindner, University of Charleston, USA. The search for life in Allan Hills 84001. Monica M. Grady, Ian. P. Wright and Colin T. Pillinger, Natural History Museum and the Open University, UK. Applications of Raman spectroscopy to exobiological prospecting. Howell G. M. Edwards and Emma M. Newton, University of Bradford, UK. Experimental investigation into present-day climate of Mars: The PMIRR experiment on the Mars Climate Orbiter. Fred W. Taylor, S. B. Calcutt and T. Vellacot, University of Oxford, UK. Low cost missions using ion propulsion. David G. Fearn, Defence Evaluation and Research Agency, UK. Is it life or is it Memorex? Why humans are essential for scientific research on Mars. Penny J. Boston, Complex Systems Research and University of New Mexico. ---------------------------------------------------------------- CASSINI MISSION STATUS REPORT JPL release 24 June 1999 The Cassini spacecraft, marking the 617th day of its voyage to Saturn, today successfully completed its second flyby of the planet Venus, once again on time and on target. As planned, Cassini came within 600 kilometers (about 370 miles) of the planet at 1:30 PM Pacific time, with Venus' gravity giving the spacecraft a boost in speed to help it reach Saturn more than 1 billion kilometers away. The spacecraft, launched on its voyage October 15, 1997, remains in excellent condition as it travels its nearly seven-year trajectory to Saturn. Most of Cassini's scientific instruments were set to make observations during the Venus flyby. Scientific data from the flyby will be transmitted to Earth over coming days. Four flybys of planets--two of Venus and one each of Earth and Jupiter--give Cassini the speed it needs to reach Saturn. Cassini first flew past Venus on April 26, 1998 at a distance of 284 kilometers (about 176 miles). Today's Venus flyby will be followed by a 1,166-kilometer (724-mile) flyby of Earth on August 18 (August 17 Pacific time at 8:28 PM PDT), then it's on to Jupiter for a December 30, 2000 flyby. The giant planet's gravity will bend Cassini's flight path to put it on course for arrival into orbit around Saturn on July 1, 2004. Cassini's mission is to study the ringed planet, its magnetic and radiation environment, moons and rings for four years. Cassini will also deliver the European Space Agency's Huygens probe to parachute to the surface of Saturn's moon Titan. Titan is of special interest partly because of its many Earthlike characteristics, including a mostly nitrogen atmosphere and the presence of organic molecules in the atmosphere and on its surface. Lakes or seas of ethane and methane may exist on its surface. The Cassini mission is a joint effort of NASA, the European Space Agency and the Italian Space Agency. The mission is managed and the Cassini spacecraft built and operated by NASA's Jet Propulsion Laboratory, Pasadena, CA. JPL is a division of the California Institute of Technology. More information about the Cassini mission is available at http://www.jpl.nasa.gov/cassini. ---------------------------------------------------------------- GALILEO--COUNTDOWN TO CALLISTO By Ron Baalke 28 June 1999 It is now 1 day, 12 hours to the Galileo spacecraft's next encounter with Jupiter moon Callisto. A special Countdown to Callisto home page is now available on the Galileo Home Page at http://www.jpl.nasa.gov/galileo/countdown/. Launched in October 1989, Galileo entered orbit around Jupiter in December 1995, and completed its primary two-year orbital tour around the solar system's largest planet. Galileo has since embarked on a two-year extended mission, called Galileo Europa Mission (GEM). During GEM, Galileo had made 8 close flybys of Europa, and will encounter Callisto four times, followed by two close encounters with Io, provided the spacecraft is still alive. The main purpose of the four Callisto flybys during GEM is to reduce the Galileo's perijove, or the closest distance to Jupiter, in order to encounter Io. The tenth encounter for GEM is scheduled for Callisto on June 30, 1999 UT. Referred to as Callisto 21, since this will occur on the 21st orbit since Galileo entered orbit around Jupiter, this encounter will be Galileo's second close flyby of Callisto during GEM. With a diameter of 4,800 km, Callisto is the third largest satellite in the solar system, and has the most cratered surface ever observed. Previous encounters by the Galileo spacecraft has found surprising evidence that Callisto may have a liquid ocean underneath its icy crust. On the upcoming encounter, the spacecraft will pass by Callisto at a distance of about 1047 km, which is over 118 times closer than Voyager's closest approach. During this encounter, observations of Io and Jupiter will also be taken. Highlights of the Countdown to Callisto home page ? A virtual flyby of Callisto with computer-generated approach images of Jupiter and Callisto displayed at the top of the home page. These images are all updated every 5 minutes in sync with the actual flyby by the spacecraft. ? Simulated animation of the Callisto 21 flyby. ? Daily Galileo status reports reporting on the Callisto 21 encounter. ? Fact sheets and Europa, Callisto and Io. ? A detailed timeline of events and sequences that the spacecraft will perform for the Callisto 21 encounter. ? Voyager 1 & 2 images of Callisto, Ganymede, Europa and Io. ? Hubble Space Telescope images of the Galilean satellites. ? Pioneer 10 & 11 images of Callisto, Ganymede, Europa and Io. ---------------------------------------------------------------- TAKING THE SCENIC ROUTE TO IO Marshall Space Flight Center release [http://science.nasa.gov/newhome/headlines/ast30jun99_1.htm] 30 June 1999 Galileo zoomed by Callisto this morning in the second of four encounters designed to bring the spacecraft closer to Jupiter's volcanic moon Io. This morning at 07:47 UT NASA's Galileo spacecraft zoomed past Jupiter's moon Callisto at a distance of only 1047 km. JPL reports that the encounter was a success and that the spacecraft is operating normally. The main purpose of today's flyby was to modify Galileo's orbit and bring the craft closer to Io, the innermost of Jupiter's large satellites. Io is one of the most exotic places in the solar system. It is literally bursting with volcanoes that spew sulfurous plumes over 300 km high. One called Prometheus may have been active for at least 18 years! In October or November, after a series of four orbit-changing encounters with Callisto (today's was the second), Galileo is scheduled to make two daring close approaches to Io, possibly flying through a volcanic plume. Although the most dramatic flybys of Io won't take place until later in 1999, scientists will get a closer look at the volcanic moon later this week when the spacecraft passes it at a distance of just 127,000 km. Galileo was within just 900 km of Io in December 1995 but the spacecraft wasn't taking pictures at that time, so this week's encounter may provide some of the best ever pictures of Io's volcanoes. "We'll also have the first real passage since 1995 through the outer edge of the Io torus during this orbit," says JPL's Dr. Torrence Johnson, the chief scientist for the Galileo mission. The Io torus is a gigantic ring of ionized gas circling Jupiter formed by sulfurous material ejected from Io's volcanoes. With a diameter the size of Io's orbit it spans 844 thousand km and has an important impact on Jupiter's magnetic environment. As Io moves along its orbit and through this magnetized plasma torus, a huge electrical current flows between Io and Jupiter. Carrying about 2 trillion watts of power, it's the biggest DC electrical circuit in the solar system. "Galileo will spend nearly a day inside the edge of the torus in an overall region of space between Io and Europa," noted Johnson. "We've been there once before in 1995. We know generally what the Io torus is and what it's made of. Now we're going to look at its detailed structure, to investigate what sort of physics is going on." Although at this point in the Galileo mission Callisto is primarily a turning point on the road to Io, it is also of considerable interest to scientists. With a diameter of 4,800 km, Callisto is nearly the same size as the planet Mercury. Its icy surface is the most heavily cratered place in the Solar System, but there are no volcanoes or even any large mountains. It is thought that little has happened to alter the surface for billions of years, other than occasional impacts with asteroids, comets, and other interplanetary debris. "One of the biggest mysteries about Callisto involves its craters," says Torrence Johnson. "As on other cratered bodies, the craters on Callisto come in all sizes. There are a few really large craters, like Valhalla, and then as you look at smaller and smaller impact features there are more and more of them. On Callisto, craters smaller than about 1 km seem to have been partially obliterated, or 'disaggregated' by some unknown process. On planets like Mars or Earth where there's been weathering or erosion, the obliteration of small craters is expected. But Callisto doesn't have a substantial atmosphere or any obvious sources of erosion, so what's happening to these craters? It's a real puzzle." "The disaggregation in small craters on Callisto is a theme for all four flybys leading up to the Io encounters," he continued. "All of the science instruments will be online during the flyby. The Solid State Imaging Camera will take high-resolution pictures that we can use to study cratering statistics. We'll also be using the Near-infrared Mapping Spectrometer (NIMS) and the UV spectrometer to get a handle on the chemical composition of the surface. We really want to examine places on Callisto that we haven't looked at before to see if the process that wipes out the small craters might be related to big impact features or to variations in the composition of the terrain." The UV spectrometer will also peer at Callisto's limb during the flyby in hopes of gleaning more information about the satellite's tenuous carbon dioxide atmosphere. Galileo's Dust Detector will be active, too, making measurements of dust particles around Callisto that might be ejecta from ongoing impact events. Another interesting story lies beneath Callisto's surface. Galileo magnetometer data released in 1998 indicate that Callisto, like another of Jupiter's moons Europa, may harbor an underground ocean. Callisto has a magnetic field that fluctuates in time with Jupiter's rotation. So far, the best explanation for Callisto's peculiar magnetism is an underground layer of melted ice. If the liquid is salty like Earth's oceans, it can carry sufficient electrical currents (induced by Jupiter's powerful rotating magnetic field) to produce a fluctuating magnetic field around Callisto. Scientists are intrigued by the prospects of an ocean on Callisto because liquid water is a prerequisite for life as we know it on Earth. "The basic ingredients for life--what we call 'pre-biotic chemistry'--are abundant in many solar system objects, such as comets, asteroids and icy moons," explained Dr. Torrence Johnson in 1998. "Biologists believe liquid water and energy are needed to actually support life, so it's exciting to find another place where we might have liquid water. However, energy is another matter, and Callisto may not have enough. Callisto's ocean is only being heated by radioactive elements, whereas Europa has tidal energy as well. That makes Europa a better prospect for life." There are many questions about Callisto, and scientists hope that the latest series of Galileo flybys will provide some answers. The next two flybys of Callisto are scheduled for August 14 and September 16, 1999, when the spacecraft's orbit will be further altered to bring it closer to Jupiter and Io. Science@NASA will continue to cover Galileo's exploits as the spacecraft heads for its dramatic encounters with Ioian volcanoes on October 11 and November 26, 1999. ---------------------------------------------------------------- THIS WEEK ON GALILEO JPL releases 21-27 June 1999 This is the last week for playback of data acquired during Galileo's May encounter with Jupiter and its moon Callisto. Next week new data will be written to the onboard tape recorder as Galileo again flies by Jupiter and Callisto. The spacecraft spends some time this week preparing for next week's encounter, thus interrupting data return. On Wednesday, playback is paused to perform a gyroscope performance test. On Friday, it is interrupted to perform a small adjustment to the spacecraft's flight path. This week's playback is a continuation of the second pass through the recorded data. This second pass allows the replay of data lost in transmission to Earth, reprocessing of data using different parameters, or return of additional new data. The data returned this week are from observations made by the Solid-State Imaging camera and Near-Infrared Mapping Spectrometer. The Solid-State Imaging camera returns observations of three different types of terrain on Callisto. The first contains images of a dark flow. The second is a set of images that will allow scientists to gather statistics on the size distribution of impact craters, which will allow them to more accurately estimate the age of the surface of Callisto. And the third is an image of Bran Crater, a young, single-ring impact crater. The formation of Bran excavated rock from deep beneath the surface and thus provides a window into the structure and composition of Callisto's crust. The Near-Infrared Mapping Spectrometer also returns observations of Callisto this week. They all contain measurements that will allow scientists to determine the chemical composition of different regions of Callisto's surface. Three observations are regional in scale, one is global, and one captures data from Bran crater and its surroundings. 3 July - 11 July 1999 The tenth encounter of the Galileo Europa Mission comes to an end on Saturday, July 3, at 4:00 am PDT (see note 1). Shortly after, Galileo begins processing images and science data stored on the spacecraft's onboard tape recorder during the previous few days and returning them to Earth. This playback of data is interrupted four times during the week. On Saturday, July 3, the spacecraft performs a standard gyroscope performance test. On Thursday, July 8, playback is paused to perform a small flight path correction, and a small turn to keep its antenna pointed toward Earth. On Sunday, July 11, playback is interrupted to allow the spacecraft to perform standard maintenance on its propulsion systems. The Solid-State Imaging camera performs several observations this morning, prior to the end of the encounter command sequence. In the first pair of observations, the camera captures Io just prior to exiting Jupiter's shadow (Io is eclipsed from the Sun by Jupiter). The observation is designed to gather data on a cloud of sodium with neutral electrical charge that has been found to exist in the vicinity of Io's orbit. These data will help scientists identify the source(s) of the cloud and advance the understanding of how sodium and other neutral elements are removed from Io. The last two observations of the encounter complete the camera's campaign to monitor Io's plume activity. The data will be used to prepare for two close flybys of Io later this year, and will also allow scientists to compare Io's volcanic activity to measurements of the Io torus made by the Fields and Particles instruments. Six observations are scheduled to be returned before the end of the week. Two are returned by the Solid-State Imaging camera, one by the Near-Infrared Mapping Spectrometer, one by the Ultraviolet Spectrometer, and two by the Photopolarimeter Radiometer. The camera's observations are high-resolution images of dark material found near a ringed structure on Callisto's surface. The images are designed to study variations in the appearance of the surface in hopes of better understanding the processes that lead to resurfacing of the surface and apparent lack of small craters. The Near-Infrared Mapping Spectrometer's observation is designed to obtain high resolution spectral and spatial data describing Callisto's surface. The data will allow scientists to identify the various materials found on the surface. The Ultraviolet Spectrometer returns an observation of Callisto's surface, which will provide additional information on surface properties. Finally, the Photopolarimeter Radiometer observations capture data describing the surface temperatures on Callisto's surface. The data will characterize relatively large regions of the surface whose temperatures are slightly higher than their surroundings They will also provide insight into how well different regions of the surface retain heat. At the end of the week, the Fields and Particles instruments begin the return of a two-hour recording made as the spacecraft flew through the Io torus. The recording contains measurements of plasma, magnetic and electric fields. The torus is a region of intense plasma and radiation activity that is constantly replenished by the volcanic activity on Io. It is a vital part of the Jovian magnetosphere. Note 1. All times listed correspond to the Pacific Time zone (currently daylight time) and spacecraft event time. Radio signals indicating that an event has occurred on the spacecraft reach the Earth 33 to 50 minutes later, depending on the time of year. Currently, Pacific Daylight Time (PDT) is 7 hours behind Greenwich Meridian Time (GMT), and it takes radio signals 44 minutes to travel between the spacecraft and Earth. For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page at http://www.jpl.nasa.gov/galileo ---------------------------------------------------------------- TODAY ON GALILEO JPL releases 29 June 1999 The tenth encounter of the Galileo Europa Mission starts today. During this encounter, Galileo performs the second in a series of four close flybys of Jupiter's moon Callisto. This series of Callisto flybys is part of the Perijove Reduction Campaign, designed to incrementally change the spacecraft's orbit to allow for a close flyby of Jupiter's volcanic moon Io later this Fall. The Perijove Reduction Campaign also provides extensive science opportunities, which include monitoring of volcanic activity on Io, exploration of the Io plasma torus, observations of Callisto, and observations of Jupiter's atmosphere and magnetosphere. During the Perijove Reduction Campaign, the spacecraft's Perijove distance, or closest distance to Jupiter for a given orbit, will be changed from one slightly higher than the orbit of Europa (9 Jupiter radii, 643,000 kilometers, or 400,000 miles) to a distance that allows Galileo to fly within the orbit of Io (5.5 Jupiter radii, 393,000 kilometers, or 244,000 miles). After the current flyby, the first two Callisto flybys will have reduced the spacecraft's Perijove distance from 9.4 Jupiter radii (672,000 kilometers, or 418,000 miles) to 7.3 Jupiter radii (522,000 kilometers, 324,000 miles). With the reduction in the Perijove distance comes an increase in the amount of radiation to which the spacecraft is exposed. Flight team members will be closely monitoring spacecraft performance during the upcoming months to diagnose and mitigate any radiation effects the spacecraft might exhibit. This week's encounter spans the next 4-1/4 days, ending early morning on Saturday, July 3. During this time, the spacecraft will be approximately 778 million kilometers (483 million miles) from Earth. It will take radio signals just under 44 minutes to travel between the spacecraft and Earth. The encounter's closest approach to Callisto occurs on Wednesday, June 30, at about 00:47 am PDT (see note 1), at a distance of 1047 kilometers (651 miles) above Callisto's surface. The start of the encounter marks the resumption of the magnetosphere survey performed by the Fields and Particles Instruments. During the survey, the instruments take measurements of plasma, dust, and electric and magnetic fields. These measurements, repeated from encounter to encounter, allow scientists to study long term variations of the inner portions of Jupiter's magnetosphere. The survey is scheduled to continue through Saturday. The radio science team begins carefully tracking the changes in the frequency of Galileo's radio signal just prior to 3:00 PM PDT. The changes are caused by Callisto's gravitational pull on the spacecraft, and the resulting Doppler shift in Galileo's radio signals. The team will track these changes for 20 hours, centered on the point of closest approach to Callisto, and will use the measurements to refine models of Callisto's gravity field and internal structure. Prior to starting any recorded observations, the spacecraft performs standard maintenance on its onboard tape recorder. There is only one recorded observation scheduled today. In it, the Near-Infrared Mapping Spectrometer obtains data of Callisto's surface at high spectral and spatial resolution. Spectral data contains information describing the light emitted from the different materials on Callisto's surface. Each material emits a unique spectrum that allows scientists to identify the given material. In conjunction, spatial data will allow scientists to determine how these materials are distributed on Callisto's surface. The information obtained in this observation is designed to further the ongoing compositional studies that were started during Galileo's primary mission. 30 June 1999 Day two of Galileo's tenth encounter of the Galileo Europa Mission features a close flyby of Jupiter's moon Callisto and science observations of Callisto performed by the spacecraft's four remote sensing instruments. The close flyby of Callisto occurs this morning at 00:47 PDT (see note 1) at an altitude of 1047 kilometers (651 miles) above Callisto's surface. This is the second in a series of four flybys that will slowly lower Galileo's orbit enough to allow the spacecraft to fly by Io in October and November of this year. A few minutes prior to the flyby, the Solid-State Imaging camera makes two observations containing high-resolution images of dark material found near a ringed feature. The observations are designed to allow scientists to study variations in the appearance of Callisto's surface in hopes of understanding the processes that modify the surface and the apparent deficit in the number of small craters. Within minutes of the flyby, the Photopolarimeter Radiometer takes a high-resolution look at a region near Callisto's equator. The observation is designed to measure the surface brightness temperatures, which will provide information about the density and composition of surface materials. The Near-Infrared Mapping Spectrometer performs the next three observations, two of which are performed in collaboration with the Ultraviolet Spectrometer. As with yesterday's single observation, these are designed to obtain high resolution spectral and spatial measurements of different regions of Callisto's surface. The spectral data will allow scientists to identify different materials on the surface, while the spatial data will help them determine where these materials lie. During one of these recordings, the Dust Detector instrument will ride along with the Spectrometer's recording, collecting data on dust particles that are concentrated near Callisto and the other Galilean satellites. These particles may be generated as small fragments of ejecta when meteorites strike Callisto's surface, remaining in orbit about Callisto for some time. The day's observing is wrapped up by three observations performed by the Ultraviolet Spectrometer. In two of them the spectrometer obtains measurements of Callisto's tenuous atmosphere. The observations are designed to allow scientists to study the potential long-term variability of the atmosphere. In the third observation, the Ultraviolet Spectrometer obtains measurements of Callisto's surface with the objective of providing more information on what materials are found on the surface. 1 July 1999 Today, the spacecraft flies through closest approach to Ganymede, Europa, Jupiter, and Io. The remote sensing instruments take advantage of today's distant flybys to make observations of Io and Jupiter. The fields and particles instruments perform a high time resolution recording of the Io torus. The torus is a region of intense plasma and radiation activity, in which there are strong magnetic and electric fields. It is constantly replenished by the volcanic activity on Io and is a vital part of the Jovian magnetosphere. Closest approach to Ganymede is first on the flyby schedule. It occurs at 5:58 PM PDT (see note 1) at a distance of 157,000 kilometers (97,600 miles). It is followed by closest approach to Europa at 9:58 PM PDT at a distance of 118,000 kilometers (73,500 miles). Closest approach to Jupiter is next on the schedule, occurring at 10:05 PM PDT at a distance of 7.3 Jupiter radii (522,000 kilometers, 324,000 miles) from Jupiter's center. Finally, closest approach to Io occurs at 10:12 PM PDT at a distance of 124,000 kilometers (77,300 miles). In the first three observations of the day, the Ultraviolet Spectrometer and the Photopolarimeter Radiometer take a look at Io, while the Near-Infrared Mapping Spectrometer looks at Jupiter. The Ultraviolet Spectrometer observation captures Io while the volcanic moon is in eclipse, shadowed from the Sun by Jupiter. The observation is designed to look at Io's atmosphere in hopes of detecting Io's auroral glow, unperturbed by sunlight. The Photopolarimeter Radiometer observation is performed later in the day and is designed to characterize regions that are low in temperature, but contain a lot of energy. The observation will also obtain temperature maps of the surface, which will provide insight into how well different regions of the surface retain heat. This is the first of three observations of this type performed by the Photopolarimeter Radiometer during this encounter. Like the previous observations of Callisto, the Near-Infrared Mapping Spectrometer observation of Jupiter is designed to obtain spectral data that will allow scientists to study different materials in Jupiter's atmosphere and advance ongoing studies. These studies address questions of Jupiter's atmospheric structure, such as cloud heights, and can obtain information on particle sizes and cloud densities, as well as information on the temperatures and composition of atmospheric constituents. Late in the afternoon, the Fields and Particles instruments perform the second in a series of recordings designed to measure the plasma, and electric and magnetic fields of the Io torus. These recordings are to be repeated during each of the four Callisto encounters of the Perijove Reduction Campaign. As Galileo's perijove distance is reduced from orbit to orbit, the Fields and Particles instruments will examine the Io torus at different distances from Jupiter. The Solid-State Imaging camera takes the stage next with a pair of observations of Io. The first series of images forms a regional map at a resolution of 1 to 1.5 kilometers (0.6-0.9 miles) per picture element. The second series of images captures a global view of Io at a resolution of 2.6 kilometers (1.6 miles) per picture element. The images taken today will provide the lowest resolution views of Io obtained by Galileo prior to the close encounters of Io that occur later this year. Toward the end of the day, the Photopolarimeter Radiometer performs the second in the series of three observations of Io's surface temperatures. The Near-Infrared Mapping Spectrometer performs the final observation of the day. It is designed to obtain high resolution spectral and spatial data of Io's surface. This will be the highest resolution map of Io made to date, including Galileo's primary mission, by the Near-Infrared Mapping Spectrometer. The spectral data will allow scientists to identify different materials on Io's surface, while the spatial data will help them determine where these materials lie. 2 July 1999 Encounter activities begin to wind down today as the spacecraft moves away from the heart of the Jupiter system and prepares for cruise operations and playback of pictures and other science information stored on the spacecraft's onboard tape recorder. Today's science observing focuses on the volcanic moon Io. There is also a single observation of Jupiter on the schedule. In the first of today's observations, the Near-Infrared Mapping Spectrometer continues to collect data showing Io's surface at high spectral resolution, and the best spatial resolution of the Galileo Europa Mission, about 60 kilometers (37 miles) per picture element. The spectral information will allow scientists to identify different materials on Io's surface, while the spatial information will help them determine where these materials lie. The Solid-State Imaging begins its Io observations by obtaining a series of images that will yield stereo images when combined with images expected to be taken later this year. These two image sets will be combined to produce stereo views at a resolution of 1.4 kilometers (0.87 miles) per picture element. The camera's next set of observations is part of a campaign to monitor Io's plume activity in preparation for two close flybys of Io later this year. These observations will also allow scientists to compare Io's volcanic activity with magnetosphere measurements made by the Fields and Particles instruments. The camera's plume monitoring observations are interrupted by two other observations, one of Io and one of Jupiter. The Io observation is performed by the Photopolarimeter Radiometer and is the third in a series designed to obtain data on Io's surface temperatures. The observation will be used to characterize relatively large regions of the surface whose temperatures are slightly higher than their surroundings. In addition, it will provide insight into how well different regions of the surface retain heat. The Jupiter observation is performed by the Near-Infrared Mapping Spectrometer and is designed to obtain spectral data of Jupiter's atmosphere. The data will allow scientists to advance ongoing studies of atmospheric structure, particle size distribution, cloud density, and temperature and composition of atmospheric constituents. Note 1. All times listed correspond to the Pacific Time zone (currently daylight time) and spacecraft event time. Radio signals indicating that an event has occurred on the spacecraft reach the Earth 33 to 50 minutes later, depending on the time of year. Currently, Pacific Daylight Time (PDT) is 7 hours behind Greenwich Meridian Time (GMT), and it takes radio signals 44 minutes to travel between the spacecraft and Earth. For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page at http://www.jpl.nasa.gov/galileo. ---------------------------------------------------------------- End Marsbugs Vol. 6, No. 18