Don Savage Headquarters, Washington, DC October 12, 1995 (Phone: 202/358-1547) Jim Sahli Goddard Space Flight Center, Greenbelt, MD (Phone: 301/286-0697) Ray Villard Space Telescope Science Institute, Baltimore, MD (Phone: 410/338-4514) NOTE TO EDITORS: 95-198 ( N95-65) NEW HUBBLE FINDINGS AND IMAGES PRESENTED AT MEETING A discovery of ozone on Jupiter's satellite Ganymede, a possible new active volcano on Jupiter's moon Io and an aurora on Saturn are among the new findings and images presented by NASA's Hubble Space Telescope scientists this week at the American Astronomical Society's 27th Annual Meeting of the Division of Planetary Sciences in Kona, Hawaii. The following is a summary of the Hubble findings and images. Images illustrating the findings are available (where noted) to news media representatives by calling the Headquarters Imaging Branch at 202/358-1900. The images also are available on the Internet as noted. "JUPITER FAMILY PHOTO" Hubble has produced a "family portrait" of the four largest moons of Jupiter, first observed by the Italian scientist alileo Galilei nearly four centuries ago. Located approximately one-half billion miles away, the moons are so small that, in visible light, they appear as fuzzy disks in the largest ground-based telescopes. Hubble can resolve surface details seen previously only by the Voyager spacecraft in the late 1970s and early 1980s. Over the past year Hubble has charted new volcanic activity on Io's active surface, found a faint oxygen atmosphere on the moon Europa, and identified ozone on the surface of Ganymede. Hubble ultraviolet observations of Callisto show the presence of fresh ice on the surface that may indicate impacts from micrometeorites and charged particles from Jupiter's magnetosphere. Hubble observations will play a complementary role when the Galileo spacecraft arrives at Jupiter in December of this year. PHOTO NUMBER: color: 95-HC-610 B&W: 95-H-621 Image files in GIF and JPEG format may be accessed on Internet via anonymous ftp from ftp.stsci.edu in /pubinfo. The same images are available via World Wide Web from URL: http://www.stsci.edu/pubinfo/Latest.html or http://www.stsci.edu/pubinfo/Pictures.html GIF JPEG Galilean Satellites gif/GalSat.gif jpeg/GalSat.jpg NEW FEATURE ON IO A pair of images of Jupiter's volcanic moon Io shows the surprising emergence of a 200-mile diameter, large yellowish-white feature near the center of the moon's disk. This is a more dramatic change in 16 months than any seen over the previous 15 years, researchers said. They suggest the spot may be a new class of transient feature on the moon. A comparison photo taken in March 1994 -- before the spot emerged -- shows that Io's surface underwent only subtle changes since it was last seen "close-up" by the Voyager 2 probe in 1979. PHOTO NUMBER: color: 95-HC-609 B&W: 95-H-620 Image files in GIF and JPEG format may be accessed on Internet via anonymous ftp from ftp.stsci.edu in /pubinfo. The same image are available via World Wide Web from URL: http://www.stsci.edu/pubinfo/Latest.html or http://www.stsci.edu/pubinfo/Pictures.html. GIF JPEG Surface Changes on Io gif/Io9495.gif jpeg/Io9495.jpg DISK AROUND STAR BETA PICTORIS THINNER THAN THOUGHT An image of a portion of a vast dust disk around the star Beta Pictoris shows that the disk is thinner than previously thought. Estimates based on the Hubble image place the disk's thickness at no more than one billion miles (600 million kilometers), or about one fourth the previous estimates from ground-based observations. The disk is tilted nearly edge-on to Earth. Because the dust has had enough time to settle into a flat plane, the disk may be older than some previous estimates. A thin disk also increases the probability that comet-sized or larger bodies have formed through accretion in the disk. Both conditions are believed to be characteristic of a hypothesized circumstellar disk around our own Sun, which was a necessary precursor to the planet- building phase of our Solar System, according to current theory. PHOTO NUMBER: B&W: 95-H-623 (no color) Image files in GIF and JPEG format may be accessed on Internet via anonymous ftp from ftp.stsci.edu in /pubinfo. The same images are available via World Wide Web from URL: http://www.stsci.edu/pubinfo/Latest.html or http://www.stsci.edu/pubinfo/Pictures.html. GIF JPEG Beta Pic Disk gif/BetaPicS.gif jpeg/BetaPicS.jpg HUBBLE PROVIDES THE FIRST IMAGES OF SATURN'S AURORA Hubble also has provided the first image ever taken of bright aurorae at Saturn's northern and southern poles, as seen in far ultraviolet light by the Wide Field and Planetary Camera 2. Hubble resolved a luminous, circular band centered on the north pole, where an enormous auroral curtain rises as far as 1,200 miles (2,000 kilometers) above the cloud tops. This curtain changed rapidly in brightness and extent over the two hour period of the Hubble observations, although the brightest emissions remained at a position fixed in sun angle, near "dawn" in the north auroral band. The image was taken on October 9, 1994, when Saturn was at a distance of 831 million miles (1.3 billion kilometers) from Earth. The aurora is produced as trapped charged particles precipitating from the magnetosphere collide with atmospheric gases -- molecular and atomic hydrogen in Saturn's case. PHOTO NUMBER: color: 95-HC-608 B&W: 95-H-619 Image files in GIF and JPEG format may be accessed on Internet via anonymous ftp from ftp.stsci.edu in /pubinfo. The same images are available via World Wide Web from URL: http://www.stsci.edu/pubinfo/Latest.html or http://www.stsci.edu/pubinfo/Pictures.html. GIF JPEG Saturn Aurora gif/SatAur.gif jpeg/SatAur.jpg HUBBLE MAPS THE ASTEROID VESTA Two maps derived from images of the asteroid 4 Vesta were taken between November 28 and December 1, 1994, with Hubble's Wide Field Planetary Camera-2, showing surface details as small as 35 miles across. Vesta is 320 miles in diameter, and the map covers a surface area of 200,000 miles. The surface brightness map shows that, The surface markings may represent ancient igneous activity such as lava flows and, in addition, regions where major impacts have stripped away the crust revealing mantle material below. The surface composition map, (a false-color composite map), shows that all of Vesta's surface is igneous, indicating that either the entire surface was once melted, or lava flowing from its interior once completely covered its surface. The map shows that Vesta has two distinct hemispheres containing two different types of solidified lava called basalts. PHOTO NUMBER: color: 95-HC-611 B&W: 95-H-622 Image files in GIF and JPEG format may be accessed on Internet via anonymous ftp from ftp.stsci.edu in /pubinfo. The same images are available via World Wide Web from URL: http://www.stsci.edu/pubinfo/Latest.html or http://www.stsci.edu/pubinfo/Pictures.html. GIF JPEG Vesta Map gif/VestaMap.gif jpeg/VestaMap.jpg HUBBLE FINDS OZONE ON JUPITER'S MOON GANYMEDE Ozone, which protects Earth's life from harmful radiation is being manufactured one-half billion miles away, on Jupiter's largest satellite, Ganymede. Hubble found ozone's spectral "fingerprint" during observations of Ganymede made by Keith Noll and colleagues at the Space Telescope Science Institute, Baltimore, MD. The amount of ozone detected on Ganymede is small by "Earthly" standards. The total is only a tiny fraction (between 1-10 percent) of the amount of ozone destroyed each winter in Antarctica's "ozone hole" (a location on Earth where ozone levels seasonally drop to extremely low levels.) Unlike ozone production in Earth's atmosphere, Ganymede's ozone is produced by charged particles trapped in Jupiter's powerful magnetic field (much like the Earth's Van Allen radiation belts). Jupiter's 9-hour, 59-minute rotation sweeps these particles along at tremendous speed, where they overtake the slower moving Ganymede and "rain" down onto the surface. The charged particles penetrate the ice surface where they disrupt water molecules, but the exact steps leading to ozone production are not yet fully understood, according to Noll. Though no atmosphere has yet been detected on Ganymede, "the evidence for all this oxygen chemistry going on in the surface ice is a strong hint that Ganymede also will turn out to have a tenuous oxygen atmosphere," said Noll. Earlier this year, Hubble detected a thin oxygen atmosphere on the Jovian moon Europa. Ganeymede, Jupiter's largest moon (3,280 miles or 5,262 km in diameter; 1.5 times the size of the Earth's Moon), is thought to be composed of rock and ice beneath which lies a water/ice mantle and rocky core. (No The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA). - end - NASA press releases and other information are available automatically by sending an Internet electronic mail message to domo@hq.nasa.gov. In the body of the message (not the subject line) users should type the words "subscribe press- release" (no quotes). The system will reply with a confirmation via E-mail of each subscription. 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