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(meteorobs) Fwd: Excerpts from "CCNet DIGEST 11/09/98"


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From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST 11/09/98
Date: Fri, 11 Sep 1998 12:30:08 -0400 (EDT)


CCNet DIGEST, 11 September 1998
-------------------------------


(1) MORE TROUBLE FOR FRANK'S MINI-COMETS THEORY
    Andrew Yee <ayee@nova.astro.utorontodot ca> 
...
(3) DPS ABSTRACTS
    Paolo Farinella <paolof@keplero.dm.unipidot it> 
...
(6) SPECTACULAR ENCOUNTER IN SPACE EXPECTED IN NOVEMBER
    DESERET NEWS
    http://wwwdot desnews.com:80/tdy/y10quabf.htm>
...
(8) SYNCHRONIC BAND FORMATION IN COMETARY DUST TAILS
    K. Nishioka, OLYMPUS OPT CO LTD
...

===============
(1) MORE TROUBLE FOR FRANK'S MINI-COMETS THEORY

>From Andrew Yee <ayee@nova.astro.utorontodot ca> 

Public Information Office
American Geophysical Union
2000 Florida Avenue, N.W.
Washington, D.C. 20009
Tel (202) 462-6900 / FAX 202-328-0566
 
September 8, 1998                                 Contact: Harvey Leifert
AGU RELEASE NO. 98-31                                      (202) 939-3212
For Immediate Release                             hleifert@kosmos.agu.org
 
"Snowball comets" are just camera noise, Berkeley researchers say 
after analyzing dark pixels in Iowa data
 
WASHINGTON, D.C. -- Researchers at the University of California at 
Berkeley have concluded that "atmospheric holes" in satellite 
imagery are caused by instrument noise in the spacecraft's own 
cameras, not by the presence of comets the size of a house 
bombarding the Earth's atmosphere every few seconds. The existence 
of such comets, sometimes referred to as snowballs in space, has 
been hotly debated since it was first proposed by Prof. Louis A.
Frank in 1986.
 
New, higher resolution images from the VIS and UVI cameras aboard 
the Polar spacecraft show similar clusters of dark pixels, which 
Frank and Dr. John B. Sigwarth, both of the University of Iowa, have 
recently taken as independent verification of the presence of small 
comets. Various critics of the comet theory have previously 
suggested that the simple explanation for the dark pixels is noise.
 
In papers scheduled for publication October 1 in the journal, 
Geophysical Research Letters, Prof. Forrest S. Mozer and Dr. James 
P. McFadden of Berkeley's Space Sciences Laboratory state that their 
study "differs from all others that have objected to the small-comet 
hypothesis in that it considers events produced by the major 
proponents of this hypothesis [Frank and Sigwarth] from data 
provided by their own Polar instrument."
 
Both papers analyze raw data for one day provided by Frank and 
Sigwarth and additional data in the form of 700,000 pixel clusters, 
covering 120 days, posted on the web and known as the Iowa catalog. 
McFadden, et al., investigate the characteristics of the dark pixels 
in relation to expected noise from the individual components of the 
two cameras. Using computer simulations, they show that the dark 
pixels seen in the satellite data from both cameras are entirely 
consistent with instrumental noise.
 
Mozer, et al., investigate the distribution of the dark pixels by 
altitude. They show that there is no appreciable height dependence. 
The researchers also note that the same pattern of dark pixels is 
seen in images of the nighttime sky as in sunlit images, which would 
not be the case if they were caused by external objects such as 
small comets. They conclude that Frank and Sigwarth's own data 
processing introduces those "meaningless" dark pixel clusters. 
Outside the radiation belt, say the authors, more than 80 percent of 
the dark pixel clusters "result from the process that Frank and 
Sigwarth employ to remove bright pixels caused by energetic 
particles."
 
GRL Space Physics and Aeronomy Editor Robert Winglee notes that 
Prof. Frank has been made aware of the contents of the Mozer and 
McFadden papers and has been invited to submit a response.
 
###
 
Note: Copies of the two GRL papers cited in this release are 
available to media representatives upon request.
 
Mozer, et. al., "Small-comet 'atmospheric holes' are instrument 
noise" 
 
McFadden, et. al., "An instrumental source for the dark pixel 
clusters in the Polar VIS and UVI experiments"
 
The papers are not under embargo. They include contact information 
for the authors.

================
(3) DPS ABSTRACTS

>From Paolo Farinella <paolof@keplero.dm.unipidot it> 
 
Benny,
 
many CCNet members may be interested in reading the abstracts of 
this year's DPS conference, which are now posted at
 
http://www.ssec.wiscdot edu/dps98/
 
Cheers,

Paolo


===============
(6) SPECTACULAR ENCOUNTER IN SPACE EXPECTED IN NOVEMBER
  
>From DESERET NEWS
http://wwwdot desnews.com:80/tdy/y10quabf.htm>
  
Editor's note: This article is a Web Edition extra that does not
appear in the printed Deseret News.
  
By Tim Radford 
The Guardian
  
Nov. 17 will be one of the more spectacular periodic encounters with 
a dust cloud from a comet.
 
Tiny fragments of stardust - the size of a grain of sand or rice - 
will hit the Earth's atmosphere at 41 miles a second, and burn up in 
a blaze of glory in the early morning sky, at the rate of at least 
one a second when Earth runs head-on into the Leonids.
 
Rocket launches will be suspended, the Hubble space telescope will 
look away and satellites' solar panels will be moved out of the line 
of fire. Meteor storms and showers are predictable - as with the
Perseids last month. But every 33 years, a group called the Leonids
provide a series of spectacular autumn encounters.
 
If this year is a disappointment, then pin your hopes on Nov. 18, 
1999, says Mark Littmann, professor of astronomy at the University 
of Tennessee at Knoxville.
 
"Back in 1966, they were estimated at as high as 40 meteors a 
second. This time around, a meteor a second would be very 
impressive. People who saw it in 1833 said it was like the heavens 
were on fire. It is like nothing else that can be seen in the night 
time sky."
 
People in the Far East will probably get the best show when the 
constellation Leo rises over the horizon after midnight. "Don't 
watch for just a minute or two, because it can come in spurts," he 
said.
 
The encounter is with a ribbon of dust shed by Comet Tempel-Tuttle. 
Meteors that burn up in the atmosphere and meteorites that hit the 
ground are a fact of life. Shooting stars appear every night. The 
guess is that Earth collects an average of 500 tons of stones, dust, 
water and gases from space every day.
 
"Over the 4 billion years the Earth has been in existence," Littmann 
says, "we have added 16 million million million tons, but even so we 
have added less than 1 percent to the Earth's mass."
 
But the Leonids are the fastest arrivals of all, because the Earth 
runs into them almost head on. Humans are in no danger. But the 
radio region of the upper sky will fizz, crackle and pop, and 
instruments orbiting above the atmosphere will be at extra risk. 
NASA engineers and satellite operators have been meeting to work out 
just how big that risk will be.
 
"Even though we are dealing with something the size of a grain of 
sand or smaller, traveling at 150,000 mph, it's like a bullet," 
Littmann said.


==================
(8) SYNCHRONIC BAND FORMATION IN COMETARY DUST TAILS

K. Nishioka: Finite lifetime fragment model 2 for synchronic band 
formation in dust tails of comets. ICARUS, 1998, Vol.134, No.1, 
pp.24-34

OLYMPUS OPT CO LTD, SHIBUYA KU, 1-43-2 HATAGAYA, TOKYO 151, JAPAN

Some big comets showed type II tails with many narrow striae called 
'synchronic bands,' the formation mechanism of which is still 
unknown. a dynamic model for the formation mechanism of synchronic 
bands, which is based on the following process, is proposed. The 
complex particles of the aggregates of the unit particles are 
ejected from the nucleus of the comet and disintegrate repeatedly 
into individual unit particles at various disintegration speeds. 
Then, these unit particles break up and their fragments are observed 
as synchronic bands. These fragments continue to disintegrate or 
sublimate into smaller pieces and finally they become too small to 
be seen at a certain normalized lifetime. The structures calculated 
with this theory fit well the observed shape and orientation of the 
synchronic bands of Comet West and Comet Seki-Lines. This dynamic 
model suggests that the radii of the complex particles and the radii 
of the unit particles are of less than visible wavelength. (C) 1998 
Academic Press


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