Comment on “Detection of small comets with a ground‐based telescope” by L. A. Frank and J. B. Sigwarth

Frank and Sigwarth (2001,JGRSP,106,A3,3665; FS) report on an optical searchfor small comets in which they report detection of nine faint trails. FS claimthat these trails are produced by low-mass, low-albedo ob-jects whose inferrednumber 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 previousunsuccessful optical search for small comets reported by Mutel and Fix (2000,JGRSP,105,24907; MF). The results of these two independent analyses of the sameimage dataset are not formally in disagreement, since all detections reportedby FS are fainter than the minimum detectable magnitude limit (16.5) determinedby MF. However, since the conclusions are quite different, we haveindependently re-analyzed the original search images for evidence of the faintdetections reported by FS. In particular, we have carefully examined whetherthe three putative trails whose positions are available satisfy severalnecessary criteria for a candidate grouping of excess-count pixels to be causedby a celestial object. While we have not evaluated the formal statisticalsignificance of faint detections, all three claimed detections fail one or moreindependent criteria required for a valid detection. In addition, both thelevel and shape of the claimed integral detection rate versus magnitude are instrong disagreement with the inte-gral number density of the small cometshypothesis. We conclude that unless the remaining claimed detections can proveotherwise, the lack of detections after "careful examination" of the 1,500search images described in FS provides the most compelling evidence yetpublished against the small comet hypothesis.Comment: 8 pages, 4 figures, accepted by JGR Space Physic