[meteorite-list] Quadrantid meteors

From: Rothery Melvin <ann.melvin_at_meteoritecentral.com>
Date: Thu Apr 22 10:18:05 2004
Message-ID: <3FF1EBFE.5EFFE2E2_at_sympatico.ca>

December 30, 2003

Core of a Comet Lights Up January's Night Sky

By KENNETH CHANG

     efore the sun rises on Sunday, the Quadrantid meteors will make
their yearly appearance,
     about one a minute streaking across the dark sky. A California
astronomer says he has
finally figured out where all those streaks of light came from.

The light shows occur when Earth crosses debris trails left by comets.

The Perseids of August come from Comet Swift-Tuttle, while a 1998 flyby
of Comet
Tempel-Tuttle generated the impressive Leonid meteors of recent
Novembers.

But the parentage of the Quadrantids (pronounced KWA-drun-tids) has been
a mystery.

Then Dr. Peter Jenniskens, an astronomer at the SETI Institute in
Mountain View, Calif., noticed
that the orbit of 2003 EH1 =97 a small asteroid discovered in March =97
"falls snug in the shower."
He claims that this is the source of the Quadrantids and that it has not
been seen until now
because it has gone dark.

The asteroid, he said, is actually the burnt-out core of a comet. Its
diameter is a little less than two
miles, Dr. Jenniskens estimated, "which is a typical size for a comet
nucleus." He has submitted
his findings to The Astronomical Journal.

The Quadrantids, discovered in the mid-1800's, are named after an
obsolete constellation,
Quadrans Muralis, the location in the sky that the meteors appear to
shoot out of. (The
International Astronomical Union phased out Quadrans Muralis in 1922.)

While they are about as intense as the Perseids, the Quadrantids are not
as well known, probably
because few are willing to stand outside at night in January to look for
them. (People in North
America should have a good view this time, though, weather permitting.
The best time will be
Sunday morning, after the moon sets and before the sun rises, or roughly
between 5 a.m. and 7
a.m., regardless of time zone. Go someplace dark =97 not Manhattan =97 wh=
ere
up to 60 meteors
an hour should be visible.)

Until now, the most likely candidate for the source of the Quadrantids
has been Comet
Machholz, discovered in 1986. But Machholz is in a different orbit, and
while Jupiter's gravity
could have separated it from the Quadrantids, no one has convincingly
shown that they are
connected.

So astronomers continued to search.

Historical records possibly mark when the comet was last seen almost
whole. Between Dec. 31,
1490, and Feb. 12, 1491, astronomers in China, Japan and Korea noted a
bright comet passing
overhead. There are no recorded sightings of that comet before or since.

A Japanese astronomer, Dr. Ichiro Hasegawa, showed some years back that
the comet's orbit
resembled that of the Quadrantids. Dr. Jenniskens guesses that the
15th-century Asian
astronomers may have been watching the disintegration of 2003 EH1. That
would explain why
the comet was so bright then but not seen at other times. "We don't know
if that object had
anything to do with the Quadrantid showers," he said, but added,
"There's a good chance."

Modern observations of the meteor shower also point to a recent breakup.
The outer part of the
Quadrantids' orbit comes close to Jupiter's and a few close encounters
with Jupiter would
disperse their orbits. But photographs taken by Dutch amateur
astronomers in 1995 indicate the
Quadrantids are still narrowly confined, suggesting that they have not
passed Jupiter many times
yet. Indeed, Dr. Jenniskens' calculations conclude that the Quadrantids
have been circling the
solar system for only the past 500 years or so.

Dr. Jenniskens also estimates that the Quadrantids total more than 10
trillion pounds of rock and
dust. "That almost certainly identifies this as a breakup of a comet,"
he said. "You have a lot of
mass, and you have a very young age."

If Dr. Jenniskens is correct, the Quadrantid meteors could offer
astronomers a unique look at the
inside of a comet. The specific colors given off by the Quadrantids as
they burn up may tell what
molecules they contain. That would be of interest to scientists studying
the origin of life on Earth
because many of the molecular building blocks for life are believed to
have formed in outer space
and then were carried to Earth by comets.

That was also the impetus for NASA's Stardust mission, which, by
coincidence, will fly by Comet
Wild 2 on Friday to collect specks of comet dust and bring them back to
Earth for study in 2006.


   Copyright 2003 The New York Times Company
Received on Tue 30 Dec 2003 04:19:59 PM PST