Comment on "Detection of small comets with a ground-based telescope" by Frank and Sigwarth

Frank and Sigwarth (2001,JGRSP,106,A3,3665; FS) report on an optical search for small comets in which they report detection of nine faint trails. FS claim that these trails are produced by low-mass, low-albedo ob-jects whose inferred number density is consistent with that predicted by the small comet hypothesis. The images used for the search were the same as those obtained in a previous unsuccessful optical search for small comets reported by Mutel and Fix (2000, JGRSP,105,24907; MF). The results of these two independent analyses of the same image dataset are not formally in disagreement, since all detections reported by FS are fainter than the minimum detectable magnitude limit (16.5) determined by MF. However, since the conclusions are quite different, we have independently re-analyzed the original search images for evidence of the faint detections reported by FS. In particular, we have carefully examined whether the three putative trails whose positions are available satisfy several necessary criteria for a candidate grouping of excess-count pixels to be caused by a celestial object. While we have not evaluated the formal statistical significance of faint detections, all three claimed detections fail one or more independent criteria required for a valid detection. In addition, both the level and shape of the claimed integral detection rate versus magnitude are in strong disagreement with the inte-gral number density of the small comets hypothesis. We conclude that unless the remaining claimed detections can prove otherwise, the lack of detections after "careful examination" of the 1,500 search images described in FS provides the most compelling evidence yet published against the small comet hypothesis.