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NASA PREPARES FOR "LAST CHANCE" METEOR SHOWER
The
early morning hours of November 19 may be your last chance to see the spectacular
Leonid meteor shower in its full glory, according to astronomers. "Even
with the full moon, this year's Leonids will probably be better than any ot
her
for the next hundred years," said Dr. Don Yeomans, an astronomer at NASA's
Jet Propulsion Laboratory, Pasadena, Calif. "If you're ever going to see
them, this might be the year to try."
The
shower is predicted to have two peaks, each a couple of hours long, during which
the most meteors can be seen. The shower's second peak, most prominent in North
American skies, is expected at around 5:30 a.m. EST, and promises the rare spectacle
of a few meteors every minute or even more. "Observers in good locations
away from city lights might see a few hundred per hour. You'll only get to see
the bright ones because the moonlight will wash out the ones that aren't as bright,"
said Yeomans. Last year, observers did not have to contend with the Moon and saw
meteors at a pace of several hundred per hour. An earlier peak is expected over
Europe and Africa the night of November 18, and observers in North America might
see a few grazers -- meteors skimming the top of the atmosphere -- from this first
peak starting around 11:30 p.m. EST Nov. 18. The
Leonids are grains of dust from comet Tempel-Tuttle colliding into the Earth's
atmosphere. Most Leonid particles are tiny and will vaporize very high in the
atmosphere due to their extreme speed (about 44 miles per second, or almost 71
km/sec), so they present no threat to people on the ground or even in airplanes.
As it progresses in its 33-year orbit, the comet releases dust particles every
time it comes near the Sun. Earth intersects the comet's debris trail every year
in mid-November, but the intensity of each year's Leonid meteor shower depends
on whether Earth ploughs through a particularly concentrated stream of dust within
the broader debris trail. The
dust that Tempel-Tuttle shed in 1866 forms the stream predicted to give Americans
a good show this year. Last year, people in Asia saw the plentiful collisions
with that stream. A dust stream from 1767 provided last year's peak hour of viewing
in North America and will provide this year's peak hour of viewing in Europe.
After 2002, Earth won't hit either of those streams again for decades to come,
and is not predicted to encounter a dense Leonid stream until 2098 or 2131. The
golden rule to watching the Leonids -- or any meteor shower -- is to be comfortable.
Be sure to wrap up warmly -- a sleeping bag placed atop a lawn chair facing east
is a good way to enjoy the show. Put your chair in a clear, dark place with a
view of as much of the sky as possible. Don't stare at any one place -- keep your
eyes moving across the sky. Most Leonids will appear as fleeting streaks of light,
but watch for the bigger ones that produce fireballs and trails -- some trails
will remain visible for several minutes or more. The Leonids get their name from
the constellation where they appear to originate; the meteors will be radiating
from the Sickle pattern in the constellation of Leo the Lion that will be rising
out of the east-northeast sky. Don't look directly at the constellation, but at
the area above and around it. And, though you don't need them to see the Leonids,
a pair of binoculars could come in handy. Researchers
think meteors might have showered the Earth with the molecules necessary for life's
origin. A two-aircraft campaign, led by astronomer Dr. Peter Jenniskens of the
SETI Institute and NASA's Ames Research Center, Moffett Field, Calif., will investigate
this possibility. "This mission is the grand finale in NASA's ongoing astrobiology
and planetary astronomy programs to study the Leonid meteor storms," Jenniskens
said. "We are looking for clues about the diversity of comets and their impact
on the chemistry of life's origin on Earth." "We
are eager to get another chance to find clues to two puzzling questions: 'What
material from space rains down on Earth?' and 'What happens to the (meteor's)
organic matter when it interacts with the atmosphere?'" said Dr. Michael
Meyer, senior scientist for astrobiology at NASA Headquarters in Washington, D.C.,
a primary sponsor of the airborne observing mission. On
Nov. 15, a team of 42 astrobiologists from seven countries will depart from southern
California's Edwards Air Force Base on a mission to Spain to observe this year's
two Leonid storm peaks. The DC-8 Airborne Laboratory, operated by NASA's Dryden
Flight Research Center, Edwards, Calif., will carry high-speed cameras, a radio
receiver to listen to upper atmosphere molecules, and a team of meteor observers,
who will keep track of the meteor activity for satellite operators concerned about
impact hazards. A
second modified NKC135-E aircraft, operated by the 418th Flight Test Squadron
at Edwards Air Force Base, will travel parallel to the NASA aircraft to provide
stereoscopic observations and spectroscopic measurements of mid-infrared and optical
meteor emissions. The
host for this year's international campaign is the Spanish Centro de Astrobiologia
(CSIC/INTA) at Torrejon de Ardoz, near Madrid, Spain, which is associated with
NASA's Astrobiology Institute (NAI), an international research consortium with
central offices located at NASA Ames. The
researchers will observe the first storm peak on Nov. 18 at 11 p.m. EST, just
after departing from Torrejon Air Force Base in Spain. They will observe the second
storm at 5:30 a.m. EST on Nov. 19 over the Great Lakes, en route to Offutt Air
Force Base in Nebraska. "This
final deployment of the Leonid Multi-instrument Airborne Campaign program promises
an important and unique database for the development of instruments targeted at
in situ sampling of cometary materials and for the future definition of comet
missions," said Dr. John Hillman, lead scientist for planetary astronomy
at NASA Headquarters. "It is hoped that these scientific data will provide
new insights for the comparative studies of comets." Although
the meteors are harmless to people, there is a slight chance that a satellite
could be damaged if it was hit by a Leonid meteoroid. The meteoroids are too small
to simply blow up a satellite. However, the Leonids are moving so fast, they vaporize
on impact, forming a cloud of electrified gas called plasma. Since plasma can
carry an electric current, there is a risk that a Leonid-generated plasma cloud
could cause a short circuit in a satellite, damaging sensitive electronic components. NASA's
Goddard Space Flight Center, Greenbelt, Md., is responsible for controlling a
large number of satellites for NASA and other organizations and is taking precautions
to mitigate the risk posed by the Leonids. These include pointing instrument apertures
away from the direction of the Leonid stream, closing the doors on instruments
where possible, turning down high voltages on systems to decrease the risk of
a short circuit, and positioning satellites to minimize the cross-section exposed
to the Leonids. Goddard
controls or manages 24 satellites in the earth and space sciences. It also manages
NASA's Tracking and Data Relay Satellite System constellation, which is controlled
from White Sands, N.M. Minimizing
the threat meteoroids pose to satellites is the second major area of NASA's Leonid
research. From five key points on the globe and from the International Space Station,
NASA researchers will use special cameras to scan the skies and report activity
around the clock during the Leonid shower. Led by Dr. Rob Suggs of the Engineering
Directorate at NASA's Marshall Space Flight Center in Huntsville, Ala., the research
is part of a long-term goal to protect spacecraft from potentially damaging meteoroids.
Using
"night-vision" image intensifier video systems and sky-watchers outfitted
with Palm computer software developed to record visual counts, NASA engineers
and astronomers will record their observations for later analysis. Another tool
at Marshall's disposal is "forward-scatter radar" -- an early warning
system built by Suggs, Dr. Jeff Anderson, also of Marshall's Engineering Directorate,
and Dr. Bill Cooke, an astronomer at Marshall. "Our
system is pretty simple," said Suggs. "We use an antenna and a computer-controlled
shortwave receiver to listen for 67 MHz signals from distant TV stations."
The transmitters are over the horizon and normally out of range. When a meteor
streaks overhead, the system records a brief ping -- the echo of a TV signal bouncing
off the meteor's trail. Like the image-intensified cameras, this system is capable
of detecting meteors too dim to see with the unaided eye. The
research data from the Leonids shower will be analyzed to help NASA engineers
refine their forecasts for spacecraft; by better determining where, when, and
how the meteors will strike, NASA can improve protective measures to prevent or
minimize damage to spacecraft. Back
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