A Rare Meteor Shower

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

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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.

Right: Jim Young photographed this Leonid fireball in 1966. [more]

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.

Above: Incoming meteoroids from Comet Bradfield will fall on Earth's southern hemisphere. These three frames depict Earth as seen from the meteoroid stream one hour before (left), during (middle) and one hour after (right) the expected outburst. Image credit: Peter Jenniskens of NASA Ames.

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.

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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 -64^o S latitude. Tucana will be just 14^o 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.

Below: Space station science officer Don Pettit looks down on Earth through the Destiny Lab window.

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@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.

"Meteor Outbursts from Long-Period Comet Dust Trails" by E. Lyytinen and P. Jenniskens will appear in the Oct. 2003 issue of Icarus.

The debris trail of Comet Bradfield (C/1976 D1) passes just inside of Earth's orbit at a distance of -0.00008 AU. A meteor outburst of about 1 hour duration is expected with a radiant at RA=+13, DEC=-64 near the star beta Tucanae. The velocity of the incoming meteoroids will be 42 km/s.

Right: Meteors from Comet Bradfield would emerge from the constellation Tucana, shown here peeking above the southern horizon of South Africa on March 1, 2003. The shower's radiant is denoted by the red dot.

International Astronomical Union circulars mentioning Comet Bradfield (C/1976 D1): IAUC 2921, IAUC 2933, IAUC 2942

Peter Jenniskens urges amateur meteor astronomers to keep a 24-hour watch for outbursts by listening to the meteor echoes reflected from faraway radio and TV stations. [more]