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ShareNov. 11, 1998 — The anticipated celestial bombardment called the Leonid meteor storm on the afternoon of November 17th (EST) won't deter NASA's Hubble Space Telescope from its key mission of gazing far across the universe -- as long as the view is in the opposite direction of the incoming meteor swarm.
Using the brilliant glow of a distant quasar located near the southern boundary of the constellation Aquarius, Hubble will probe galaxy formation and the distribution of matter in space. The Hubble data will become immediately available to the astronomical community.
The meteor storm is an expected downpour of thousands of meteors zooming by Earth. They pose a small but potential threat to Hubble and other satellites, say experts. The meteors appear to come from the direction of the zodiacal constellation Leo the Lion, and hence the storm is called the Leonids.
For a 10-hour period at the peak of the storm, estimated to be at approximately 2:43 p.m. Eastern Standard Time on the 17th, the telescope will be oriented with its aft bulkhead facing into the direction of the meteoroid stream. Hubble's solar panels will lay flat, or parallel to the meteoroid flow.
Though most Leonid meteoroids are smaller than a grain of sand, they zoom across space at a menacing 155,000 miles per hours. A speck-sized meteoroid can pack the wallop of a .22 caliber bullet as it pierces the spacecraft hull.
Still, even at the peak of meteor activity the density of particles in any given region of space is extremely low. So, project scientists predict that Hubble has less than a 1-in-10,000 chance of being hit by a particle large enough to pierce it's aluminum skin.
Smaller meteoroids vaporizing on impact create a plume of plasma that can short-circuit spacecraft electronics. However, a short circuit on Hubble is unlikely because its electronics are housed inside aluminum boxes that also serve as a meteoroid shield.
The Space Telescope won't be idle during the shower. STScI director Steven Beckwith is making his discretionary observing time available so astronomers can still observe the heavens while the orbiting observatory is aimed away from the meteoroid barrage.
Hubble will be aimed at a quasar, the bright core of an active galaxy, approximately 10 billion light-years away. Hubble won't be studying the quasar itself but the surrounding galaxies, protogalaxies and primordial hydrogen clouds between us and the quasar. The quasar is so brilliant, it is like a searchlight shining through fog.
Strung along billions of light-years, like beads on a string, the gas clouds will be detectable in the way they subtract certain colors or frequencies of the quasar's light. The observation will help determine whether the clouds are cold primeval hydrogen or are sites of ongoing star formation which have been enriched with heavier elements.
Hubble's Space Telescope Imaging Spectrograph will take a long-exposure picture to identify galaxies along the sight, and divide the light into a rainbow of colors (a spectral image) to determine galaxy distances. This is accomplished by measuring how the light has been stretched or redshifted by the universe's expansion.
Follow-up spectroscopic observations with large ground-based telescopes and high-resolution spectrographs will measure the quasar light directly and identify the distance of the intervening gas clouds.
The redshifts of the gas clouds from the ground-based data will then be matched with the redshifts of the galaxies along the line of sight seen in the HST data. These combined observations will allow astronomers to see if galaxies are associated with these invisible clouds.
LEONID STORM HISTORY
The Leonid meteor storm occurs as Earth passes through a region of concentrated, fresh debris within the stream that follows Comet P/55 Tempel-Tuttle.
The comet made its last closest passage to the sun in late February of this year. Warmed by the sun, the icy comet nucleus spewed a great deal of dust into space as its ices melted. These dust particles appear as meteors when they enter Earth's atmosphere and burn up from friction.
The stunning estimates of as many as 10,000 meteors during the 1-hour storm are based on prior meteor storms that have occurred when the comet has returned to Earth during the past 2 centuries.
Because the comet has a 33-year period, the last shower was on November 17, 1966. A brief, 20 minute burst in meteor activity -- as seen from the central and western United States lit up the skies with 40 meteors per second!
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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 Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).
This release and an illustration is available on the Internet at http://oposite.stsci.edu/pubinfo/1998/40 and via links in http://oposite.stsci.edu/pubinfo/latest.html.
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