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New Optical Search:
Different Telescope,
Same Small Comets
Part 1
A second ground-based telescope has acquired images of the small comets.
Between October 1998 and May 1999 astronomers at the University of Iowa used the
Iowa Robotic Observatory (IRO), located in the Sonoran desert near Sonoita, Arizona,
to search for the small comets in the vicinity of Earth on moonless nights. A thorough
analysis of the images produced by this search was conducted by two physicists at
the University of Iowa, Louis A. Frank and John B. Sigwarth. A paper which details
their findings, "Detections of Small Comets with a Ground-Based Telescope,"
has been published in the March 1, 2001 issue of the Journal of Geophysical Research-Space
Physics.
The new search yields further confirmation of the presence of small comets in the
vicinity of Earth. The IRO obtained some 6,000 images during the search period, but
due to malfunctions, unfavorable atmospheric conditions, and other circumstances,
only 1,500 images were usable for study. After a careful analysis, Frank and Sigwarth
were able to identify nine small comets in these images. The nine events identified
as "small comets" are quite distinct from noise.
The search method, which was designed by Frank and Sigwarth, helped to rule out spurious
events. In order to separate the detection of small comets from random events due
to fluctuation in the pixel responses in the images, a shutter was used during the
exposure of each image. This shutter broke up the small comet trail in two or three
depending on whether two or three exposures were taken during the single image. Subsequent
analysis shows that in the two trail mode no events were seen with three trails,
and in the three trail mode no events were seen with two trails. Further assurance
that the trails were not due to noise was provided by the high signal to noise ratios
in the small comet trails.
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