HUBBLE SPACE TELESCOPE: A NEW VIEW OF THE UNIVERSE COPY FOR SCIENCE NEWSLETTER - "THE OBSERVER" This premier issue of the HST Observer presents a selection of early scientific findings gleaned from the two cameras aboard NASA'S Hubble Space Telescope. Early observations demonstrate that Space Telescope is unsurpassed in its capabilities despite the spherical aberration at the heart of the telescope's 2.4- meter primary mirror (see page 5). There is no ground-based optical telescope which has better resolution, or can view the universe in the ultraviolet region of the spectrum. The early observations presented in this issue provide spectacular views of two of the Solar System's most celebrated objects, Pluto and Saturn. HST observations of the Orion Nebula, Supernova 1987, and a nearby nova remnant provide intriguing new glimpses of star birth and death. Hubble Space Telescope is already expanding scientific frontiers and rapidly opening a new golden age for astronomy. A STORM ON SATURN The spectacular cover image of the planet Saturn was taken with Space Telescope's Wide Field and Planetary Camera on August 29, 1990 when the planet was at a distance of 1.39 billion kilometers (860 million miles) from Earth. Once image reconstruction techniques are applied to compensate for aberration, new details snap into focus which have never before been photographed from Earth. The Encke division, a dark gap near the outer edge of the broad ring system is clearly visible, as well as atmospheric features at northern polar hood, which is presently tilted toward Earth. Within weeks of this historic first picture amateur astronomer Stuart Wilber detected a white spot on Saturn. Mission planners at Space Telescope Science Institute rescheduled HST observing time to view this rare storm which erupts every 30 years. When HST looked again at Saturn in early November, Coriolis forces and wind shear had smeared the spot into a broad white belt. The massive storm appeared only as a white blob in earth-bound telescopes but HST images revealed a rapidly changing scalloped structure, resembling the cloud bands of Jupiter. The immense storm, which grew larger than Jupiter's Red Spot, probably begins when moist material from deep within Saturn's atmosphere bubbles up to the cloud tops to form ammonia ice crystals. Like injecting a milky dye into a stream of water, these bright white cirrus cloud-like features allow astronomers a rare opportunity to trace the dynamics of Saturn's otherwise bland atmosphere. [page 3] A HALO FOR A DEAD STAR Though the great supernova of 1987 has all but faded away astronomers continue to intensively study the explosive aftermath. It's like listening for the bang from a firework, long after seeing the burst of light. Observations made with ESA's Faint Object Camera (FOC) show clearly for the first time the rapidly expanding cloud of debris form the explosion, which has mushroomed to a diameter of .1 light-year. An added bonus is a detailed look at a ghostly "footprint" left behind by the supernova's progenitor star. This eerie relic appears as a luminescent ring surrounding the site of the blast. The ring could not have been produced by the supernova explosion because it is more than one light-year across. The expanding clouds of debris from the supernova haven't had nearly enough time to fill a volume of space as large as the ring. This means the ring must have existed before the star exploded, but how did it get there? The ring is probably part of an invisible shell of gas that was ejected by the parent star. Old massive stars swell up to become red supergiants that shed much of their outer layers into space, like an imaginary balloon that never stops inflating. The supernova's progenitor star later evolved back to a hot blue supergiant giant and lost gas even more vigorously. This rapidly expanding bubble of material eventually plowed into the older shell, compressing part of it into a peculiar narrow ring. The ring is visible today because it was heated by the blast of energy it received from the supernova flash. This "halo" of the dead star will be destroyed in less that 100 years when it is engulfed by the rapidly expanding debris from the supernova. During its relatively short existence, the glowing ring has given us an important new clue about the final years of a giant star's life. THE DOUBLE PLANET REVEALED Space Telescope's Faint Object Camera has clearly resolved the disk of Pluto and its moon Charon. When the picture was taken Charon was at it maximum separation from Pluto (an angle of only headlights at a distance of 500 km). The two icy worlds are 20,000 kilometers apart, a distance merely 1.5 times Earth's diameter. Thirty times farther from the Sun than Earth, Pluto is an elusive planet. Discovered merely 60 years ago, Pluto is the only planet that has not been visited by a space probe. Pluto's moon Charon wasn't discovered until 1978. It took nearly 50 years to detect the moon because, when photographed by ground-based telescopes, the pair appears blurred into a single egg-shaped object. HST observations will allow for precise measurements of the masses and densities of Pluto and Charon, and their respective orbits about each other. Since Charon is one-half the diameter and approximately one-eighth the mass of Pluto, the two worlds are often referred to as the double planet. They complete one rotation about each other once every six days. HST may provide new clues to the origin of this double planet. Neither a terrestrial nor Jovian-type planet, it may be the last survivor of a population of large icy bodies that inhabited the young Solar System. [page 5] INSIDE THE GREAT ORION STAR FACTORY The majestic Orion Nebula is a favorite target of astronomers, professional and amateur alike. The most spectacular nearby star forming region in the galaxy (1500 light-years away), it provides a ringside seat for studying the details of stellar birth. A Wide Field and Planetary Camera engineering test image of a one light-year square section of the Orion nebula reveals a network of arcs, filaments and other intricate structures. This new level of detail reveals about 30 knots of gas which fluoresce under the flood of ultraviolet radiation from the nearby Trapezium star cluster, at the very center of the nebula. Hot stellar winds from the young stars eat into cooler denser gas along the edge of the nebula to produce a "shower curtain" structure. The image also reveals one apparent by-product of star formation: "jets" of hot gas which escape away from stars condensing out of the nebula. One of the more prominent jets extends for about one-tenth of a light-year. [page 6] REPORT ON HUBBLE SPACE TELESCOPE'S MIRROR FLAW: A CASE OF ABERRANT BEHAVIOR Any basic telescope-making book for amateur astronomers describes spherical process, where an improperly curved mirror does not bring light to a single focus. HST's mirror was ground a little too shallow, its edge being .002 millimeters too low. The mirror was polished to a perfectly smooth, but wrong shape, because the optical template used for grinding and then verifying the figure of the mirror was incorrectly assembled. This critical piece of testing and calibration equipment is called the reflective null corrector. The device essentially projects the desired shape of the mirror onto the actual mirror in the process of its fabrication. Then by reflecting light off that mirror back up through the reflective null corrector, engineers can obtain an interference pattern which tells how close the mirror is to the desired figure. The aberration essentially throws away 85% of a star's light into a broad halo (not unlike looking at a car's headlights through a hazy windshield). Nevertheless, the remaining starlight is still concentrated into a tiny core image that is much sharper than a comparable ground based view. This means that HST has not lost resolution, the ability to separate two objects, but rather sensitivity, the ability to see very faint objects. HST can still yield three to ten times better resolution, but it cannot meet the original goal of detecting objects 50 to 100 times fainter than can be accomplished with ground-based telescopes. Fortunately many of the exciting objects in the universe have sufficient contrast and brightness so that their images are not ruined by the spherical aberration. However some of HST's ambitious science program is significantly compromised until the science instruments are outfitted with corrective optics to compensate for the mirror's shortcomings. NASA is planning to fix the Space Telescope by 1993 when the Space Shuttle returns for routine maintainence. IN SEARCH OF A LOST NOVA Space Telescope conducted a needle-in-the-haystack search for a star which briefly erupted 60 years ago. The star is now lost amid 100,000 other stars in what is known as a globular star cluster M14, which is 70,000 light years away. The detective hunt has not yet uncovered the star but it has provided an unprecedented view of the crowded inner region of the globular star cluster. Space Telescope resolves hundreds of separate stars in a tiny region of the cluster where only dozens are distinguishable in ground-based images. The star called attention to itself 1/2 century ago when it grew 10,000 times brighter than normal. Such a stellar outburst is called a nova, when a star briefly flares up but doesn't destroy itself. Once the nova dimmed back to normal brightness it vanished among the cluster's myriad other stars, which are concentrated in a patch of the sky smaller than the apparent size of the full Moon. The most widely accepted theory today is that all novae are in fact two stars locked in a close orbit by their mutual gravitational attraction. One member of the pair is a normal star while the companion is a dense white dwarf star. The dwarf pulls hydrogen gas off the outer layers of the companion star. Periodically, the accumulated hydrogen detonates through nuclear fusion, like an immense hydrogen bomb. The nova in M14 was accidentally photographed in 1938 with the 72-inch telescope at the David Dunlap Observatory near Toronto, Canada. However it wasn't until 25 years later that this nova was actually discovered when an astronomer studying the photographic plate found the telltale nova as a bright pinpoint of light. This was only the second time in astronomical history where a nova was seen within the globular cluster's dense concentration of stars. HST reveals six separate stars in the nova's suspected location, where previous ground-based images show only one blob of light. However none of these candidates have an unusual excess in ultraviolet light, which would be one characteristic of the nova's binary system. So the search will continue by using the HST's Faint Object Spectrograph to observe each star in the region to look for the typical " spectral signature" of a nova. One single binary system can potentially dominate the motions of all the stars within a globular cluster because it has far more kinetic energy locked up than all the single stars combined. That's because the close stellar pair whirl about each other at a million-kilometers per hour. This creates a powerful "storage battery" of kinetic energy. A bypassing star drifting at only few kilometers per second, can rob some of the binary system's energy and get a boost in speed, like a pinball bouncing off of a bumper. [page 8] A STELLAR VOLCANO The double-star system R Aquarii is one of the closest stars known to undergo periodic nova-like outbursts. The ESA Faint Object Camera provided the first close-up look at the "reactor core" of this binary system. The image reveals a 400 billion kilometer-long rapidly moving geyser of plasma. The luminescent streams are twisted by the force of the nova explosion and channeled upwards and outwards by strong magnetic fields. This stellar blowtorch erupts from two very bright knots which probably harbor the double star system which produces the fireworks (the knots show up as dark spots in the picture due to saturation effects produced by the detector when it observes very bright objects). One member of the R Aquarii system is a cool red giant star. The red giant may periodically spill some of its mass onto its companion star which is a white dwarf. When the companion becomes overloaded with infalling gas it explodes, blasting material back into space along two jets. IN THE NEXT ISSUE: - HST's First Spectroscopic Observations - A New Global View of Mars - The Search for Galactic Black Holes The HST Observer is published quarterly by the Educational and Public Affairs Office of the Space Telescope Science Institute. ----------------------------------------------------------------- [masthead] Science Editor Ray Villard Production Manager Cheryl Gundy Astronomy Illustrator Dana Berry Design John Godfrey