[meteorite-list] Return of the Leonids

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 4 Dec 2008 14:38:49 -0800 (PST)
Message-ID: <200812042238.OAA07452_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/headlines/y2008/04dec_leonids2009.htm

Return of the Leonids
NASA Science News
12.04.2008

Dec. 4, 2008: Astronomers from Caltech and NASA say a strong shower of
Leonid meteors is coming in 2009. Their prediction follows an outburst
on Nov. 17, 2008, that broke several years of "Leonid quiet" and heralds
even more intense activity next November.

"On Nov. 17, 2009, we expect the Leonids to produce upwards of 500
meteors per hour," says Bill Cooke of the NASA Marshall Space Flight
Center. "That's a very strong display."

Forecasters define a meteor storm as 1000 or more meteors per hour. That
would make the 2009 Leonids "a half-storm," says Jeremie Vaubaillon of
Caltech, who successfully predicted a related outburst just a few weeks ago.

On Nov. 17, 2008, Earth passed through a stream of debris from comet
55P/Tempel-Tuttle. The gritty, dusty debris stream was laid down by the
Leonids' parent comet more than five hundred years ago in 1466. Almost
no one expected the old stream to produce a very strong shower, but it
did. Observers in Asia and Europe counted as many as 100 meteors per hour.

Vaubaillon predicted the crossing with one-hour precision. "I have a
computer program that calculates the orbits of Leonid debris streams,"
he explains. "It does a good job anticipating encounters even with very
old streams like this one."

The Nov. 17, 2008 outburst proved that the 1466 stream is rich in
meteor-producing debris, setting the stage for an even better display in
2009.

On Nov. 17, 2009, Earth will pass through the 1466 stream again, but
this time closer to the center. Based on the number of meteors observed
in 2008, Vaubaillon can estimate the strength of the coming display:
five hundred or more Leonids per hour during a few-hour peak centered on
21:43 UT.

"Our own independent model of the debris stream agrees," says Cooke. "We
predict a sub-storm level outburst on Nov. 17, 2009, peaking sometime
between 21:34 and 21:44 UT."

The timing favors observers in Asia, although Cooke won't rule out a
nice show over North America when darkness falls hours after the peak.
"I hope so," he says. "It's a long way to Mongolia."

Many readers will remember the great Leonid showers of 1998-2002. The
best years (1999 and 2001) produced storms of up to 3000 Leonids per
hour. The 2009 display won't be so intense. Instead, if predictions are
correct, next year's shower could resemble the 1998 Leonids, a
"half-storm"-level event caused by a stream dating from 1333. That old
stream turned out to be rich in nugget-sized debris that produced an
abundance of fireballs. Many observers consider the 1998 Leonids to be
the best they've ever seen.

Could 2009 be the same? Vaubaillon expects a similar number of meteors
but fewer fireballs. If the models are correct, the 1466 stream in
Earth???s path contains plenty of dust but not so many nuggets, thus
reducing the fireball count. On the bright side, the Moon will be new
next Nov. 17th so nothing will stand in the way of the shower reaching
its full potential.

Mark your calendar and stay tuned for updates from Science at NASA.
Received on Thu 04 Dec 2008 05:38:49 PM PST