'Snowball Comets' Are Just Camera Noise, Berkeley Researchers Say After Analyzing Dark Pixels In Iowa Data

September 08, 1998

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.

American Geophysical Union

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