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U P D A T E # 3 3 Part 1: Chat with
the Galileo Probe Heroes A special opportunity is coming to get interactive with the women and men behind the Galileo Probe. Key players from the management, engineering and science teams will be available this coming May 15 (Wednesday) from 4:00-9:00PM Pacific time. The discussion will take place at a special WebChat area made just for this purpose. The URL is http://quest.arc.nasa.gov/webchat/galileo.html To participate on that night, you need only to have a forms-capable Web browser. Please join us with some well thought-out questions.
Although this is a bit off topic, we thought that many folks interested in
the Galileo mission would also be interested in NASA's upcoming missions
to Mars. This summer you'll have an opportunity to virtually meet Mars
experts and prepare for a real adventure. If you think youa re interested,
please respond now to this free offer:
Passport to Knowledge/ NASA K-12 Internet Initiative
NASA Jet Propulsion Lab
presents for the FIRST TIME EVER.....
THE MARS "VIRTUAL" TEACHER TRAINING CONFERENCE
JULY 20, 1996
via the
Internet and Video Conferencing
Dear Educators,
This July marks the 20th anniversary of the Viking Landings on Mars and
1996 will see new American and Russian missions to the Red Planet.
LIVE FROM MARS, the next electronic field trip from PASSPORT TO KNOWLEDGE
(sponsored in part by NSF/NASA and public television), will connect students
across the country with NASA's Mars Pathfinder and Mars Global Surveyor
missions via four live telecasts, print hands-on curriculum materials,
and on-line resources from November 1996 through November 1997.
A three day teacher workshop to help educators prepare to implement
"Live from Mars" in their classroom is being planned for July 18th-20th
in Washington, DC, site of the Viking Celebrations. Teachers attending
the workshop will include representatives from each state, many of whom
have actively participated in PASSPORT TO KNOWLEDGE projects over the
past three years. Guest speakers include astronomer Carl Sagan, NASA
Administrator Dan Goldin, NASA JPL Mars Pathfinder and Global Surveyor
mission scientists and experts. Optimizing the integration of electronic
field trips and the Internet in the classroom are also topics of the upcoming
workshop.
PASSPORT TO KNOWLEDGE and NASA intend to abolish the constraints of
time and space (and travel budgets!), by experimenting with a Virtual
Workshop
on Saturday July 20th. Depending in part on response to this announcement
we will proceed with all, some, or none of the options below.
We would like to extend an invitation to educators everywhere who
would benefit from attending the Saturday, July 20th workshop "virtually"
through the use of on-line interaction via email, CuSeeMe, Web Chats and
web-based resources as well as video conferencing at host sites. Virtual
participants will have opportunities to interact live via participation in
electronic mail forums, on-line Question and Answer opportunities,
interactive chat sessions and via CuSeeMe and will have access to all
support curriculum materials via the World Wide Web. Through this *first
time ever* PTK/NASA sponsored virtual conference the same professional
development experience will be available to all educators, regardless of
their geographical proximity to the live workshop.
It is *critical* to our project to have host sites --- local universities,
science centers, planetariums, corporate sponsored sites, education support
agencies, K-12 institutions --- which can serve as a local *hosts* for
participation in the on-line workshop. These sites would be responsible for
providing information, a local meeting area, access to the Internet
(web/CuSeeMe), and access to NASA TV . If you represent such a site and
are interested in such sponsorship, please contact Andrea McCurdy, NASA K-12
Internet Initiative, by emailing her at
April 8, 1996 The Galileo spacecraft continues to play back tape-recorded probe science data of measurements made in Jupiter's atmosphere last Dec. 7, filling all gaps left in prior transmissions. In addition, since March 26 it has been collecting and transmitting measurements of Jupiter's magnetosphere and dust environment, similar to those made on the way to Jupiter. Telemetry indicates that Galileo is operating normally, and all the instruments are in good condition. Eight instruments are powered on, but only the magnetometer and dust detector are returning science data at this time. The spacecraft is spinning at about 3 rpm, and transmitting science and engineering data at 16 bits per second. After a thorough analysis of telemetry from the propulsion system, Galileo engineers decided to increase the spacecraft electric power margin, which will allow propellant temperatures and pressures to increase safely. Increasing the power margin permits flexibility in spacecraft operations, starting in late June with scientific observations of Ganymede, Io and Jupiter's Red Spot. The engineers have also finalized the procedures for using the tape recorder during that encounter to obtain images and other science data. They believe these procedures will carry the spacecraft through all fault scenarios. The Galileo spacecraft is 18.7 million kilometers (11.6 million miles) from Jupiter, 19.7 million kilometers (12 million miles) from Ganymede, and 775 million kilometers (482 million miles) from Earth. April 15, 1996 Galileo's playback of the tape-recorded science data obtained by the atmospheric probe in Jupiter's atmosphere Dec. 7 was successfully concluded early this morning. The probe science team has presented preliminary results at a meeting in Houston and will publish a group of papers in Science magazine next month. Orbiter spacecraft measurements of the Io plasma torus, made a few hours before the spacecraft arrived at Jupiter, remain to be played back starting in June when the spacecraft has been reprogrammed with its new software. Later this week a new test sequence for the tape recorder will condition the tape and further explore the limits of safe use of the tape. A fairly conservative procedure for data recording will be used for the Ganymede encounter in June. The better the engineers understand the tape and the way it sticks, the better use they can make of it in later encounters, project officials said. Development and testing of the new flight software is progressing reasonably well. It involves reprogramming of the main flight computers in the command and data subsystem and attitude and articulation control system and in nine science instruments. The engineers believe that the process of installing this in the Galileo spacecraft, starting in May, will take less time than planned, though a few enhancements due this week will delay the start of loading. The software will be used in playing back the orbiter's Io torus data, beginning in June. May 1, 1996 The Galileo spacecraft is operating normally in orbit around Jupiter, continuing to collect and transmit information on the magnetic field and dust environment and to prepare for the first Ganymede encounter just eight weeks away. The experimenter teams have not yet fully analyzed the magnetometer and dust data collected since late March. However, an initial look indicates, as expected, very few particles detected because the dust detector was pointed away from the planet during this part of the orbit. In the two-day tape recorder test last week, the tape stuck and was successfully unstuck many times under various conditions. The engineers are gaining confidence in operating the tape recorder. They believe that these test results support the strategy established to deal with the sticking problem, starting with the Ganymede encounter. Later this week Galileo will perform its first small orbit trim maneuver to refine the path to Ganymede. The velocity change of about 1.3 meters per second (less than 3 mph) will move the arrival about 35 minutes later and considerably closer to the satellite. Ganymede encounter at 844 kilometers (about 520 miles) altitude is planned for June 27. In about two weeks Galileo's new flight software will be transmitted to the spacecraft via the Deep Space Network. The new software, for Galileo's command and data subsystem, attitude control subsystem and most of the scientific instruments, is currently finishing up testing in the spacecraft test-bed simulator at JPL. May 3, 1996: Jupiter's volcano-pocked moon Io has been found by NASA's Galileo spacecraft to have a giant iron core that takes up half its diameter, scientists report in today's issue of Science magazine. The spacecraft also has detected a large "hole" in Jupiter's magnetic field near Io, leading to speculation about whether Io possesses its own magnetic field. If so, it would be the first planetary moon known to have one. These newly identified characteristics of Io may be related to the intense heating of the moon caused by the constant squeezing and distortion of Io in Jupiter's powerful gravitational grip, according to Galileo Project Scientist Dr. Torrence Johnson of NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA. Io is the most geologically active body in the Solar System, and though it is less than a third of Earth's size, it generates twice as much heat as the Earth. "Jupiter's massive gravity field distorts the shape of Io in the same way that tides are raised in Earth's oceans by the gravitational tugs of the Sun and Moon," Johnson said. As Io orbits Jupiter, these so-called "body tides" rise and fall due to subtle changes in Io's orbit which in turn are caused by the gravitational nudges from Europa and Ganymede, other moons of Jupiter. As a result, Io is squeezed like a rubber ball. Friction created by this action heats and melts rock within Io to produce the volcanoes and lava flows seen all over its surface, and huge geysers that spew sulfur dioxide onto Io's landscape. The large, dense core Galileo found within Io was deduced from data taken during the spacecraft's flyby within 559 miles of the moon last Dec. 7, as Galileo passed by the moon on its way to enter orbit around Jupiter. Precise measurements of the spacecraft's radio signal revealed small deviations in Galileo's trajectory caused by the effects of Io's own gravity field. >From these data, Galileo scientists have determined that Io has a two-layer structure. At the center is a metallic core, probably made of iron and iron sulfide, about 560 miles in radius, which is overlain by a mantle of partially molten rock and crust, according to JPL's Dr. John Anderson, team leader of Galileo's celestial mechanics experiment and principal author of the paper published in Science today. The core was probably formed from heating in the interior of the moon, either when it originally formed or as a result of the perpetual tidal heating driving its volcanoes. Galileo scientists also are trying to determine the cause of the hole they found in Jupiter's magnetic field when the spacecraft was closest to Io. "Instead of increasing continuously as the spacecraft neared Jupiter, the magnetic field strength took a sudden drop of about 30 percent," Johnson said. "It's an astonishing result and completely unexpected," said Dr. Margaret Kivelson of the University of California at Los Angeles, who heads Galileo's magnetic fields investigation team. Preliminary analyses of these data are currently being prepared for formal publication. "The data suggest that something around Io -- possibly a magnetic field generated by Io itself -- is creating a bubble or hole in Jupiter's own powerful magnetic field," Kivelson said. "But it's not clear to us just how Io can dig such a deep and wide magnetic hole." Possible explanations for this signature can only be sorted out using data from all the other space physics instruments onboard Galileo, Johnson said. "We're eagerly awaiting the return of data from the magnetospheric measurements taken during the Io flyby to see if we can resolve this mystery," he said. This data, recorded on board the spacecraft, will be transmitted back to Earth in June or July. If analysis of this data eventually proves that Io indeed has a magnetic field of its own, it would be the first moon shown to have one. Io would join the Earth, planet Mercury and the outer giant planets as bodies in our Solar System that generate their own magnetic fields. Other studies conducted by Galileo during its December flyby of Io have provided new evidence that Io is most likely the source of high-velocity dust streams littering millions of miles of space around Jupiter. In July 1994, Galileo's dust detector began sensing dust streams more powerful than those previously discovered by the Ulysses spacecraft. Dust detectors on Galileo sensed more and more particles during its approach to Jupiter, reaching a peak of 20,000 impacts per day during the longest and most intense interplanetary dust storm ever observed. These fast-moving particles travel at speeds from 30 to 60 miles per second away from Jupiter -- fast enough to escape the Solar System. These dust impacts continued up to the time of Galileo's Io flyby and then ceased, said Dr. Eberhard Grun of Germany's Max Planck Institute in Heidelberg, principle investigator for Galileo's dust detector experiment. "My preliminary interpretation of these observations is that they support the idea that Io is in some way the source of the Jupiter dust streams," Grun said. One theory proposed after the NASA Voyager spacecraft flybys in the late 1970s is that dust particles emitted from Io's volcanoes could become electrically charged and then swept away by Jupiter's rotating magnetic field. Recent modifications to this theory suggest that the dust is subsequently accelerated in the magnetosphere and flung outward from Jupiter at high velocity, creating dust streams. Galileo's next close encounter with a moon of Jupiter will occur June 27, when the spacecraft will pass about 530 miles above the surface of Ganymede. Larger than Mercury, Ganymede is the largest moon in the Solar System. Galileo will make repeated close flybys of Ganymede, Callisto and Europa during its two-year mission in orbit around Jupiter. To obtain a copy of the Science magazine article (Dr. John Anderson et al) reporting the new findings on Io's core, contact the AAAS Office of Communications, 202/326-6421. May 9, 1996 Galileo continues normal operations in orbit around Jupiter this week, transmitting science and engineering telemetry at 16 bits per second, while the flight team at JPL analyzes the flight path adjusted by last week's maneuver and the health and performance of the spacecraft. The orbit trim maneuver performed last Friday slightly changed the spacecraft's arrival time and geometry for the Ganymede encounter on June 27, as planned. This was the first trajectory correction using the small 10-newton thrusters since late August 1995. There is an opportunity for another trim maneuver in June if it is needed. Tomorrow's issue of Science magazine will carry reports by Galileo probe scientists who are based at NASA's Ames Research Center in Mountain View, Calif., and at other laboratories. The issue also features articles by Earth-based observers on their studies of Jupiter's atmosphere and environment, which are derived from data collected during the probe's descent into Jupiter's atmosphere on Dec. 7, 1995. Next Monday, May 13, the Galileo team will begin installation of massive new flight software in the spacecraft, transmitting the computer code in installments over a period of 10 days to two weeks. This will almost double the software used by the main spacecraft computers in the command and data subsystem. Galileo is now 15.7 million kilometers (9.8 million miles) from Jupiter, coming closer at a rate of 1.9 kilometers (1.2 miles) every second. It is currently 701 million kilometers (436 million miles) from Earth, so that each digital bit of the flight software going to the spacecraft next week will take a little less than 39 minutes to reach the spacecraft. Larry Palkovic April, 1996 The article below is from the April 1996 issue of the Galileo Messenger, the official newsletter of the Galileo mission to Jupiter. This issue covers missions activities through the exciting Jupiter orbit insertion and the successful probe mission. The entire issue is also available on the Galileo home page: http://www.jpl.nasa.gov/galileo/ After a 6-year journey replete with nail-biting trials and eye-popping triumphs in space, and after a frustrating 6-week delay back on Earth, the Galileo Probe's bounty of scientific data was finally presented, on January 22 at the Ames Research Center, to a fascinated public by a panel of Probe science investigators headed by Probe Scientist Rich Young (see photo). Their preliminary report summarized the condensed memory readout from the Orbiter's solid-state memory downlinked in December and January. In the months since that meeting, subsequent analyses have changed some of the scientists' earliest views on their data. Probe investigators are still waiting for the complete playback from the Orbiter's tape recorder, but that won't be finished until mid-April. While the picture of Jupiter that has emerged is, generally, similar to what was expected, the details are sufficiently different to merit some serious rethinking on the origin and structure of the planet and its atmosphere. The Probe was certainly well prepared for its brief but celebrated exploration of the Jovian atmosphere. Radio contact with the Orbiter was solid for almost an hour, and every instrument performed perfectly through the nominal mission. The approach and entry were not without some surprises. The space between Jupiter's rings and atmosphere was expected to be fairly quiet, but Harald Fischer's energetic particle instrument discovered a new, powerful radiation belt here---populated by high-energy helium ions and ten times stronger than Earth's Van Allen belt. Probe deceleration in the upper atmosphere as measured by Al Seiff's atmospheric structure instrument was greater than expected, indicating a much denser (100 times) and hotter (227 deg C) atmosphere 340 km above the 1-bar level. Unexpected, too, was a parachute deployment 53 seconds late and 26 km below the planned 0.1-bar level. When the heat shield dropped off and the instruments started recording, Larry Sromovsky's net flux radiometer (NFR), designed to measure the energy balance between the Sun above and the planet below, showed variations in sky brightness that indicated scattered clouds. At this 0.4- to 0.6-bar level (-150 deg C to -130 deg C and 20 km above the 1.0-bar level), these were likely ammonia clouds. Boris Ragent's nephelometer, which reads a reflected laser beam for cloud particles, saw none at this altitude, suggesting the ammonia clouds were distant, or at least scattered. Maybe 45 or 50 km further down, however, at about 2 bars (-70 deg C), it did record substantial concentrations of what were believed to be ammonium hydrosulfide clouds. While well defined, even these clouds were not nearly as thick as postulated; the NFR did not report them. Even further down, 60 to 80 km below 1 bar, at the 5- to 8-bar level where temperatures support liquid water (0 to 40 deg C), the nephelometer found no evidence for water clouds, though these should have been the thickest of all. Glenn Orton's ground-based, infrared telescopic observations showed the Probe's entry site to sit on the edge of a prominent "hot spot." This broad patch of clearer, drier atmosphere looked to be a region of thinner, even absent clouds. This certainly confirmed the nephelometer readings and suggests that, at least in its upper atmosphere, Jupiter is a very heterogeneous planet. One of the principal tasks of the investigators will be to distinguish those data that measure local phenomena from those that measure the global. Hasso Nieman's neutral mass spectrometer, which determines the composition of the atmosphere, also revealed the atmosphere to be drier than expected---much drier than predicted from Shoemaker-Levy 9 data, and even drier than predicted from Voyager data! Initial results suggested generally Sun-normal values for many other atmospheric constituents, but later work has changed that picture. Solar values would suggest little change in Jupiter's evolution from the original solar nebula, but increased concentrations of any element (besides hydrogen and helium) would suggest a history of cometary accretions. Concentrations of methane and hydrogen sulfide were greater than solar values. Ammonia values, even at this date, still puzzle researchers. Concentrations of the noble gases krypton and xenon were much greater than solar values, but isotopic ratios were near solar. Fewer organic molecules and substantially less neon than expected also characterized the Jovian atmosphere sample. Ulf von Zahn's helium abundance detector measured the concentration of helium at 0.24 by mass, close to solar abundance. Low levels of helium indicate depletion in the atmosphere of Saturn, but this is not seen at Jupiter, probably because of Jupiter's larger size (three times more massive) and higher internal temperatures. Lou Lanzerotti's lightning and radio emission detector looked for both optical flashes (from near discharges) and radio waves (from more distant ones). The expected thick cloud decks suggested lots of cloud-to-cloud bolts. In retrospect, considering the lack of water clouds, it's not surprising that no flashes were seen. On the other hand, the Probe did record the radio signatures of perhaps 50,000 strikes---up to an Earth's diameter away. These numbers translate to very powerful discharges but to only a third (or even a tenth) the occurrence rate of lightning on Earth. Fewer strikes are also consistent with fewer organic molecules (which the strikes generate). Dave Atkinson's Doppler wind experiment tracked the Doppler shift in the Probe's radio signal to measure the speed of the Jovian winds. Wind speed at the cloud tops was thought to be 360 to 540 km/h, and this was expected to drop to zero at some point---if, as on the Earth, such winds are generated by sunlight and release of latent heat by condensation of water vapor. Not unexpectedly, Jupiter is not like the Earth. Winds are faster than expected, clocking 720 km/h below the cloud-top level, and show no tendency to slow with depth. Jovian winds are apparently generated by heat coming from below. The helium abundance detector stopped recording at 14 bars, as designed, after 40 minutes of activity. At this time, signals from the nephelometer and net flux radiometer also became useless as they degraded to noise. After 48 minutes of recording, 110 km down, the instrument shelf temperature inside the Probe was much closer to the outside 15-bar temperatures of 100 deg C than the expected 50 deg C. The lightning detector and neutral mass spectrometer stopped sometime after this point. Only Al Seiff's atmospheric structure instrument was still operating when radio transmission stopped after 57.6 minutes at the 23-bar level (152 deg C, 140 km down). This instrument measured the atmospheric temperature, pressure, and densities during the entire 160 km or so (20 km above 1.0 bar to 140 km below) of descent. During the entry phase, it showed hotter temperatures and higher densities than expected in the upper atmosphere, and numbers much closer to those expected in the lower atmosphere. Also consistent with Doppler data, it showed that the Probe dropped through a very turbulent atmosphere. And consistent with the other instruments, it measured a lapse rate or change of temperature with altitude that showed a very dry atmosphere in the 6- to 15-bar range and convective transfer of heat, which powers the wind systems and keeps the deep layers well mixed. After its last transmission, the Probe, we imagine, continued to sink into the Jovian depths. Without a surface to hit, the Probe lost its Dacron parachute, its aluminum fittings, and even (by the 5000-bar level, 1700 deg C) its titanium shell to melting and evaporation. Ten hours after entering the atmosphere there would have been nothing left to see, and the Probe would have become a part of the planet that its sister Orbiter will be watching so closely. The Probe science team eagerly awaits the return of the last bits of the taped Probe data set. These data, along with additional atmospheric data from the Orbital tour, will keep the team busy for years unwrapping the secrets of this mysterious giant. If this is your first message from the updates-jup list, welcome! We are presently in a down mode where an update will be sent about once per month. We hope to reactivate the project more fully after a variety of science data begins streaming in. The likely timeframe for any such reactivation is early 1997. To catch up on back issues, please visit the following Internet URL: gopher://quest.arc.nasa.gov:70/11/interactive-projects/jupiter/journals
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