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American Geophysical Union
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September 8, 1998 Contact: Harvey Leifert
AGU RELEASE NO. 98-31 (202) 939-3212
For Immediate Release email@example.com
"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