[meteorite-list] A Rare Meteor Shower

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:18:31 2004
Message-ID: <200302281756.JAA06419_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/headlines/y2003/28feb_tucanids.htm

A Rare Meteor Shower
NASA Science News
February 28, 2003

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.
Received on Fri 28 Feb 2003 12:56:57 PM PST