Are Meteor Showers Misunderstood?

http://www.seti.org/site/apps/nl/con...179&ct=1016671

FOR IMMEDIATE RELEASE
June 14, 2005

Contact information:
Karen Randall, Director of Special Projects, SETI Institute
Phone: 650-960-4537

Are Meteor Showers Misunderstood?

NASA's Deep Impact mission is about to smash into comet 9P/Tempel 1 to
excavate a crater and probe the comet's internal structure. It's
possible, however, that the comet will break into fragments, creating a
cloud of meteoroids. That, say astronomers, may not be unnatural.

"If comet 9P/Tempel 1 breaks during NASA's Deep Impact mission on July
4, a meteoroid stream will be created in much the same manner as the
mechanism that causes most of our meteor showers," according to SETI
Institute astronomer Dr. Peter Jenniskens in a paper accepted for
publication in the Astronomical Journal .

Jenniskens has discovered a fragment of lost comet D/1819 W1
(Blanpain),
last seen in 1819. It has survived for 36 orbits, and was detected on
November 22, 2003 by the Catalina Sky Survey as a minor planet called
2003 WY25. It passed Earth at a distance of only 0.025 AU (3.7 million
kilometers) on December 11, 2003. After its orbit was better
determined,
Jenniskens traced the object back to that of Blanpain in 1819. 2003
WY25
is a tiny object, only 400 meters in diameter, assuming that, like
similar objects, it reflects about 4% of the sunlight that hits it.

Jenniskens and co-author Esko Lyytinen, an amateur astronomer from
Finland, calculated how the debris of a breakup in 1819 would have
spread under the influence of planetary perturbations. They
discovered
that a breakup during (or just before) the return of 1819 can explain a
spectacular shower of meteors that radiated from the constellation of
Phoenix in 1956. In that year, the planet Jupiter had steered the trail
of debris into Earth's path.

"The 19th century idea that meteor showers originate from the breakup
of
comets went into remission after astronomer Fred Whipple, in 1951,
developed a quantitative description of meteoroid acceleration by the
drag of water vapor," says Jenniskens. "Ever since, meteor showers were
thought to be caused by the gradual ejection of meteoroids when the
comet's ices evaporated on approach to the Sun."

Instead, it now appears that many meteoroid streams are caused by
wholesale disintegration of comets, which are loose assemblages of
cometesimals and are known to frequently break apart. There are several
possible causes of such fragmentations, one of which is collisions with
large meteoroids such as simulated in the Deep Impact mission.

Last year, Jenniskens identified minor planet 2003 EH1 in the orbit of
the strong Quadrantid shower of January, and argued that the object was
the residue of a broken comet giving rise to the Quadrantid shower. A
comet seen in A. D. 1490 - 1491 (C/1490 Y1) was perhaps the
manifestation of that breakup.

The detection of 2003 WY25 provides a second example of the formation
of
a meteoroid stream by the disintegration of a comet. Other well known
meteor showers that likely originated from the breakup of a comet,
according to Jenniskens, include the December Geminids (with remnant
3200 Phaethon), as well as the June Daytime Arietids and July
delta-Aquariids that are associated with the Marsden-group of
sun-skirting comet fragments. It is now also likely that the
spectacular
meteor storms of Andromedids in 1872 and 1885 were due to the
progressive fragmentation of comet 3D/Biela in 1846 and 1852.

Dr. Jenniskens is chair of the Pro-Amat working group of Commission 22
(meteoroids and interplanetary matter) of the International
Astronomical
Union.

Reference:

P. JENNISKENS, E. LYYTINEN, 2005. METEOR SHOWERS FROM THE DEBRIS OF
BROKEN COMETS:
D/1819 W1 (BLANPAIN), 2003 WY25 , AND THE PHOENICIDS. Astronomical
Journal (in press).

Read the paper
http://www.seti.org/atf/cf/{B0D4BC0E-D59B-4CD0-9E79-113953A58644}/WY25d.pdf

CV: http://leonid.arc.nasa.gov/pjenniskens.html