NASA Prepares for “Last Chance” Meteor Shower

The early morning hours of Nov. 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 other 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,” he said. NASA is taking
advantage of
the event for several research efforts around the world.

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
Nov.
19, 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 Nov.
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 within 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 for 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 Leo the Lion, which 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. “We are
looking for
clues about the diversity of comets and their impact on the chemistry
of
life’s origin on Earth,” Jenniskens said.

“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.

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.

“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,” he said.

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.

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.

For more information, including predicted peak times for major cities
and
NASA media contacts, refer to:

http://www.gsfc.nasa.gov/topstory/2002/1114leonid.html