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(meteorobs) ESA Science News: "Wish Upon A Shooting Star -- The Geminids Meteor Shower Peaks Tonight"
------- Forwarded Message
From: Ron Baalke <baalke@zagami.jpl.nasadot gov>
Subject: Wish Upon A Shooting Star -- The Geminids Meteor Shower Peaks Tonight
Date: Thu, 13 Dec 2001 09:35:46 -0800 (PST)
ESA Science News
http://sci.esa.int
13 Dec 2001
Wish upon a shooting star -- the Geminids meteor shower peaks tonight
Meteor watchers in Europe may be compensated for missing last month's
splendid Leonid meteor storm when the annual Geminids shower peaks in
the early hours of Friday morning. Up to 100 shooting stars per hour
may be visible if observing conditions are good.
The Geminids meteor shower is an annual event triggered by the passage
of Earth through the outskirts of a dusty debris cloud thrown off by a
rocky asteroid called 3200 Phaethon.
Although nowadays regarded as one of the best meteor showers of the
year, this was not always the case. Prior to the 1860's there were no
recorded sightings of Geminids. Their appearance seems to have been
fairly sudden -- the first shower was recorded in 1862, surprising sky
watchers who saw 15 or so unexpected shooting stars each hour. Those
early showers were unimpressive, but since then the Geminids have
grown in intensity.
"Generally speaking, this shower is not as intense as the 2001 Leonids
shower," says ESA scientist Detlef Koschny, "but compared to what was
visible here in Europe in November, this will be more spectacular. The
night is also going to be dark: no Moon will disturb the observations."
Most meteor showers are an effect of debris that boils off a comet's
nucleus when it passes close to the Sun. This debris then begins to
orbit, along with the parent comet, forming a stream of meteoroids
that become shooting stars when they hit Earth's atmosphere.
"The case of the Geminids, however, is a bit peculiar," says Detlef
Koschny. "This is one of the very few cases known where the meteor
trail results from debris left by an asteroid instead of a comet. The
rocky asteroid, called 3200 Phaethon, was discovered in the 1980's.
This unusual parent body means that, even if the difference is not
visible to the naked eye, scientists will be able to distinguish the
particles generating the shooting stars: they will not be fluffy, but
rather stony."
Scientists have a few ideas to explain the odd phenomenon of an
asteroid forming a debris tail. One explanation could be that there
was an impact with a smaller body which produced the dust. Another
explanation is that asteroids and comets are perhaps just two
extremes of the same phenomenon: when it has more ice, we call it a
comet; when there are more silicates (material containing silicon
and oxygen), we call it an asteroid. Perhaps Phaethon's ice has
vapourized and the Geminids are the leftovers of a former comet.
Whatever the explanation, ESA's Rosetta mission, due to be launched
in 2003, will shed more light on this hypothesis with its remote
observations of Comet Wirtanen and its in-situ investigation of
Wirtanen's nucleus.
In the meantime, for those brave enough to challenge the rigours of
a winter night, the shooting star show begins tonight, after sunset.
The best chance of seeing meteors is in the morning hours before
dawn.
Enjoy!
USEFUL LINKS FOR THIS STORY
* More about comets and asteroids
http://sci.esa.int/structure/directory/index.cfm?aid=5&cid=84
* More about the Leonids
http://sci2.esa.int/leonids/leonids2001/
* More about Rosetta
http://sci.esa.int/rosetta/
* Tips for observing the Geminids
http://www.spaceweather.com/meteors/geminids/observingtips.html
IMAGE CAPTION:
[http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=12&oid=29152&
ooid=29163]
Wish upon a shooting star tonight. In this photograph a Leonid meteor
streaks through the sky across a star field containing the planet
Jupiter, and the constellations Orion and Gemini. Image courtesy of
Ferris Hall [http://www.ferrishall.com/stars/].
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