Call it "The Sounds of Distant Ganymede."
     At a JPL press conference December 12, Galileo project scientists provided the latest results from the analysis of data taken from Ganymede flybys in June and September, including an audio recording based on data collected by the spacecraft's plasma wave instrument.
     The audio recording consists of hissing static and soaring whistles and helped the scientists determining that Ganymede has its own magnetosphere, the only moon in the solar system known to possess one.
     Donald Gurnett, a University of Iowa scientist that is the principal investigator on the plasma wave experiment, said the "unique pattern of frequencies detected" clearly showed that Ganymede has its own, internally-created magnetosphere. "The instant I saw the spectrogram, I could tell we passed through a magnetosphere at Ganymede," he said.
     JPL planetary scientist John Anderson combined that result with extremely precise tracking of the spacecraft to get information on the interior composition of Ganymede. According to Anderson, the moon has a metallic core 400 to 1250 km (250 to 800 miles) in radius. The core is surrounded by a rocky silicate mantle, which is in turn surrounded by an icy crust 800 km (500 mi.) thick.
     These and other results were published in a series of articles in the journal Nature.
     Galileo is now gearing up for a close flyby of Europa, scheduled for December 19. Scientists released images of the moon taken earlier in the mission, which showed the surface of the moon may be very young, only 30 to 50 million years old.
     Scientists theorized that "cryovolcanism", including spreading centers of darker matter seen in some images, may recycle the Europan crust and keep the moon's surface young.

A giant 9-meter (355-inch) telescope, the largest in the continental United States, saw "first light" December 10th at McDonald Observatory in Texas.
     The Hobby-Eberly Telescope (HET), a joint project of the University of Texas, Penn State University, Stanford University, and two German universities, took images of stars in the first observing test of the advanced telescope.
     Like the slightly larger 10-meter Keck telescopes in Hawaii, the HET consists of 91 1-m hexagonal mirror segments. The alignment of the segments are controlled by computers. However, unlike the Keck and most other telescopes, the entire telescope does not move to track objects across the sky, but rather moves a few focusing instruments suspended above the mirror to track objects.
     The large telescope, located at McDonald Observatory in the west Texas mountains, will be used primarily for spectroscopic observations, including the search for new extrasolar planets, study galaxies and black holes, and look for clues about the early history of the universe.
     The HET cost only $13.5 million dollars, or less than a fifth of the cost of each Keck telescope. "We are very pleased that we have been able to stay within the established HET budget and have progressed from groundbreaking to first light in less than three years," said Thomas Sebring, HET project manager.
     Sebring said the tests will continue into next year, with the official commissioning of the telescope in late 1997. Australia, Chile, and South Africa have expressed interest in building a southern hemisphere counterpart for the HET.

More than a year after the launch of the Infrared Space Observatory, European scientists are celebrating the wealth of data returned by the spacecraft.
     In a special issue of the journal Astronomy and Astrophysics, 91 articles based on ISO research, mostly by European authors, were published. The topics of the articles ranged from studies of the formation of planets to observations of "ultra-luminous" galaxies, which may harbor giant black holes.
     "The 91 papers published this month, covering observations from planets to galaxies, are still only a foretaste of many hundreds to be expected as observing programs and the data processing mature," said Martin Kessler, ISO project scientist.
     ISO, launched by an Ariane 4 rocket in November 1995, is about halfway through its operational lifetime. ESA officials plan to keep ISO operational through December 1997.
     Although ISO is a European projects, agreements with the United States and Japan have given astronomers from these countries limited participation in ISO observations.