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NASA Science News for February 28, 2003

A Rare Meteor Shower
====================

Earth is approaching a cometary debris stream that might trigger an
unusual Antarctic meteor shower this weekend. 

February 28, 2003: "We all felt like we needed to put on 'hard hats'!
The sky was absolutely full of meteors," recalls astronomer Jim Young
of JPL's Table Mountain Observatory. Earth had just plunged into a
debris stream trailing comet Tempel-Tuttle; the resulting meteor
storm, the 1966 Leonids, was literally dazzling. 

This weekend it could happen again.

On March 1, 2003, around 2154 universal time (UT), our planet will
encounter a stream of dusty comet debris "only 12,000 km from Earth.
That's as close as the Leonid debris stream was in 1966," says Bill
Cooke of the NASA Marshall Space Flight Center's Space Environments
Team. 

The source of the dust this time is Comet Bradfield (C/1976 D1)--a dim 
comet discovered in 1976 by Bill Bradfield of Australia. It swings 
through the inner solar system approximately every 1000 years. 

"We've never observed a meteor outburst from Comet Bradfield before,"
says Cooke. That's no surprise: The comet's orbit is tilted so the
shower is visible only from the far-reaches of our planet's southern
hemisphere. The best viewing spots are near the coast of Antarctica 
... "and onboard the International Space Station," adds Cooke.

Researchers are interested in this remote shower because of its
source: a long-period comet. 

Most meteor showers, like the Leonids, are caused by short-period
comets that circle the Sun every few years or decades. These frequent
visitors are easy to find and are routinely tracked by astronomers.
Long period comets, on the other hand, spend most of their time in the 
dark recesses of space beyond Pluto; the vast majority remain
undiscovered. With little warning one could swoop in from the outer
solar system and pass uncomfortably close to our planet. 

Peter Jenniskens of the NASA Ames Research Center and the SETI
Institute thinks meteor showers might provide a distant early warning
system for such objects. He and colleague Esko Lyytinen recently
examined the orbits of dust from all known long-period comets and
identified five potential new showers during the next 50 years--
including this weekend's. Although Comet Bradfield doesn't pose a
threat to Earth, says Jenniskens, it might show us what a "long-period 
meteor shower" looks like.

Jenniskens is traveling to Cape Town, South Africa. "I'll try to
observe this outburst with the help of members of the Astronomical
Society of South Africa, led by Tim Cooper," he says. Even at the
southern tip of Africa, though, meteors will be difficult to see. The
shower's radiant is in the constellation Tucana, the Toucan, which
passes overhead at -64o S latitude. Tucana will be just 14o above the
horizon of Cape Town during the expected peak, its low altitude
greatly reducing the number of visible meteors. "I'll be happy to see
any at all," says Jenniskens. 

Astronauts have a better view. "The International Space Station will
be over the southern hemisphere in an excellent position to view any
meteors from this event," says Cooke. Looking out the station's
windows, members of the crew might be able to spot meteoroids
disintegrating in the atmosphere below. "Even if it turns into a
full-fledged meteor storm, which I doubt, there's no danger to the
heavily-armored station," he says. The crew can relax and enjoy the
show. ( Recommended reading: Science{at}NASA's "Space Station Meteor
Shower.") 

This isn't the first dust trail from a long-period comet Jenniskens
has studied. In 1995, members of the Dutch Meteor Society assisted him 
in triangulating meteors from a spectacular burst of alpha-
Monocerotids over Spain that year. They demonstrated that the dust was 
in a long period orbit (much longer than 150 years). "That shower
proved long-period comets have dust trails," he says. "And it showed
peculiar aspects such as sodium-poor meteoroids with unusually high
density." 

Are those the telltale signs of a long-period comet? This weekend's
outburst could provide valuable data. Or not. It may be that no one
has ever seen meteors from Comet Bradfield because there are none to
see. Yet Jenniskens doesn't need a dazzling storm like the 1966
Leonids to learn what he wants to know. Even a few shooting stars on
March 1st would be a big event. 

Editor's note: After Antarctica and the ISS, the next best places to
observe this shower are South Africa and the southwestern coast of
Australia. Because the shower is expected to be brief, it is important 
to watch at the right time: between 2054 and 2254 UT on March 1, 2003.

Credits & Contacts
Author: Dr. Tony Phillips
Responsible NASA official: Ron Koczor 
Production Editor: Dr. Tony Phillips 
Curator: Bryan Walls 
Media Relations: Steve Roy

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