[meteorite-list] Strange Lights: The 2007 Aurigid Meteor Shower

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 10 Aug 2007 09:29:26 -0700 (PDT)
Message-ID: <200708101629.JAA22534_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/headlines/y2007/08aug_aurigids.htm

Strange Lights: The 2007 Aurigid Meteor Shower
NASA Science News
August 8, 2007

August 8, 2007: Will they come, or will they not? That is the question.

On Sept. 1, 2007, a flurry of bright and oddly-colored meteors
might???emphasis on might--come streaming out of the constellation Auriga,
putting on a beautiful early morning show for sky watchers in western
North America: sky map
<http://science.nasa.gov/headlines/y2007images/aurigids/skymap_north.gif>.

The source of the putative shower is Comet Kiess (C/1911 N1), a
mysterious "long-period comet" that has visited the inner solar system
only twice in the past two thousand years. In 83 BC, give or take a few
centuries, Comet Kiess swung by the sun and laid down a trail of dusty
debris that has been drifting toward Earth's orbit ever since. On Sept.
1, 2007, the dusty trail and Earth will meet.

But will a shower actually materialize? The answer lies in the unknown
contents of the debris stream.

"We have so little experience with ancient debris from long-period
comets," notes Bill Cooke of NASA's Meteoroid Environment Office (MEO)
at the Marshall Space Flight Center. "Almost anything could happen???from
a fizzle to a beautiful meteor shower."

Astronomers were first alerted seven years ago to the possibility of a
shower by Finnish astronomer Esko Lyytinen and Peter Jenniskens of the
SETI Institute in Mountain View, CA???both are accomplished meteor
forecasters who study the dynamics of cometary dust trails. Jenniskens
has since teamed with Jeremie Vaubaillon of Caltech to refine the
forecast using a debris stream model developed by Vaubaillon.

"We expect the outburst to peak at 11:36 UT (4:36 a.m. PDT) +/- 20
minutes on Sept. 1st," says Jenniskens. "The whole event should last
about 2 hours and be visible from California, Oregon, Hawaii and the
eastern Pacific Ocean."

An independent model of the debris stream calculated by Danielle Moser,
a colleague of Cooke at the MEO, predicts a peak time of 11:26 UT.
"That's in good agreement with Jenniskens and Vaubaillon," says Cooke.
"However, our model predicts a mostly empty stream and a very weak shower."

"Personally, I think the meteor rate will reach 100 per hour at best,"
notes Vaubaillon, "but some colleagues are more optimistic, so,
suspense, suspense!!!"

Earth has had at least three encounters with the debris stream in the
past century - in 1935, 1986, and 1994. Unfortunately, few people were
outdoors paying attention. The best observed encounter was in 1994 when
veteran meteor watchers Bob Lunsford and George Zay of southern
California witnessed a number of bright blue-green meteors emerging from
Auriga. The brief shower was remarkable both for its conspicuous lack of
faint meteors and for the vivid colors--characteristics that may be
repeated on Sept. 1st.

Meteors from long-period comets are of special interest for two reasons:

#1 -- Long period comets almost always take us by surprise. They linger
in the outer solar system, hiding in the dark for thousands or millions
of years, until their slow orbits turn them sunward and--in they plunge!
Because of this surprise factor, long period comets pose a unique impact
threat. Jenniskens and others are keen to study meteor showers from long
period comets because the showers could be a "tell" that a comet is out
there, and the orbit of the meteoroids can reveal where.

#2 -- Meteors from long period comets may be very primitive. Consider
the following: Most meteor showers (e.g., the Perseids and Leonids) are
caused by short period comets, which pass through the inner solar system
every few decades or, at most, centuries. Their icy surfaces are
frequently heated and vaporized by intense sunlight, and the comet dust
they produce is correspondingly fresh. Long period comets, on the other
hand, are rarely sun-blasted, and their surfaces may retain ancient
substances formed by billions of years of cosmic ray exposure in the
outer solar system. Flakes from this "pristine crust" may produce odd
colors when they hit Earth's atmosphere.

Is that why the Aurigid meteors of 1994 were blue-green? Were they bits
of pristine crust from Comet Kiess? Again, no one knows.

Jenniskens notes that another
meteor outburst, the alpha Monocerotids of 1995, also thought to hail
from an unknown long-period comet, was strange: "The alpha-Monocerotids
penetrated 5 km deeper in the atmosphere than other meteors of similar
size and speed and they had [an unusually] low content of sodium."

To get to the bottom of some of these mysteries, Jenniskens and
colleagues from the NASA Ames Research Center, Utah State University,
the USAF Academy and elsewhere will board two private jets to observe
the Aurigids from the clear air of 45,000 feet. They'll use
spectrometers, cameras and telescopes to measure the velocity,
penetration, and chemical composition of incoming meteoroids.

Bill Cooke of the MEO won't be on board, but he wishes the flyers well.
"If this shower actually happens, they data they collect may tell us new
things about an important population of meteoroids in the solar system.
Plus, it would be a good show for people on the ground."

Sept. 1, 2007: The answers await.
Received on Fri 10 Aug 2007 12:29:26 PM PDT