The anticipated celestial bombardment called the Leonid meteor stormon the afternoon of November 17th (EST) won't deter NASA's Hubble SpaceTelescope from its key mission of gazing far across the universe -- aslong as the view is in the opposite direction of the incoming meteorswarm.
Using the brilliant glow of a distant quasar located near the southernboundary of the constellation Aquarius, Hubble will probe galaxyformation and the distribution of matter in space. The Hubble datawill become immediately available to the astronomical community.
The meteor storm is an expected downpour of thousands of meteorszooming by Earth. They pose a small but potential threat to Hubble andother satellites, say experts. The meteors appear to come from thedirection of the zodiacal constellation Leo the Lion, and hence thestorm is called the Leonids.
For a 10-hour period at the peak of the storm, estimated to be atapproximately 2:43 p.m. Eastern Standard Time on the 17th, thetelescope will be oriented with its aft bulkhead facing into thedirection 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, theyzoom across space at a menacing 155,000 miles per hours. A speck-sizedmeteoroid can pack the wallop of a .22 caliber bullet as it piercesthe spacecraft hull.
Still, even at the peak of meteor activity the density of particles inany given region of space is extremely low. So, project scientistspredict that Hubble has less than a 1-in-10,000 chance of being hit bya particle large enough to pierce it's aluminum skin.
Smaller meteoroids vaporizing on impact create a plume of plasma thatcan short-circuit spacecraft electronics. However, a short circuit onHubble is unlikely because its electronics are housed inside aluminumboxes that also serve as a meteoroid shield.
The Space Telescope won't be idle during the shower. STScI directorSteven Beckwith is making his discretionary observing time available soastronomers can still observe the heavens while the orbitingobservatory 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 studyingthe quasar itself but the surrounding galaxies, protogalaxies andprimordial hydrogen clouds between us and the quasar. The quasar is sobrilliant, it is like a searchlight shining through fog.
Strung along billions of light-years, like beads on a string, the gasclouds will be detectable in the way they subtract certain colors orfrequencies of the quasar's light. The observation will help determinewhether the clouds are cold primeval hydrogen or are sites of ongoingstar formation which have been enriched with heavier elements.
Hubble's Space Telescope Imaging Spectrograph will take along-exposure picture to identify galaxies along the sight, and dividethe light into a rainbow of colors (a spectral image) to determinegalaxy distances. This is accomplished by measuring how the light hasbeen stretched or redshifted by the universe's expansion.
Follow-up spectroscopic observations with large ground-basedtelescopes and high-resolution spectrographs will measure the quasarlight directly and identify the distance of the intervening gasclouds.
The redshifts of the gas clouds from the ground-based data will thenbe matched with the redshifts of the galaxies along the line of sightseen in the HST data. These combined observations will allowastronomers to see if galaxies are associated with these invisibleclouds.
LEONID STORM HISTORY
The Leonid meteor storm occurs as Earth passes through a region ofconcentrated, fresh debris within the stream that follows Comet P/55Tempel-Tuttle.
The comet made its last closest passage to the sun in late February ofthis year. Warmed by the sun, the icy comet nucleus spewed a greatdeal of dust into space as its ices melted. These dust particles appearas 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-hourstorm are based on prior meteor storms that have occurred when the comethas returned to Earth during the past 2 centuries.
Because the comet has a 33-year period, the last shower was onNovember 17, 1966. A brief, 20 minute burst in meteor activity -- asseen from the central and western United States lit up the skies with40 meteors per second!
The Space Telescope Science Institute is operated by the Association ofUniversities for Research in Astronomy, Inc. (AURA) for NASA, undercontract with the Goddard Space Flight Center, Greenbelt, MD. The SpaceTelescope is a project of international cooperation between NASA and theEuropean Space Agency (ESA).
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