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(meteorobs) Leonid Meteor Storm Won't Deter Hubble From Space Observations


FOR RELEASE:  9:00 a.m. (EST) November 10, 1998

CONTACT:  Ray Villard
          Space Telescope Science Institute, Baltimore, MD
          (Phone:  410-338-4514)
          (e-mail: villard@stscidot edu)

PRESS RELEASE NO.:  STScI-PR98-40


LEONID METEOR STORM WON'T DETER HUBBLE FROM SPACE OBSERVATIONS

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!

                      *****

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.stscidot edu/pubinfo/1998/40 and via links in
http://oposite.stscidot edu/pubinfo/latest.html.

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