Small comets: Naked‐eye visibility

Abstract

Abstract. We investigate an obvious consequence of the small-comet hypothesis. We find that the 30-ton cloud of water-ice particles formed by a small comet would survive long enough to be an unmistakably bright object. The visual magnitude of such clouds would be between that of a bright star and the full Moon. A whole-Earth small-comet flux of 20/rain implies the sudden appearance of at least two bright patches of light every five minutes. The two-hour periods after sunset and before sunrise ought to produce the most spectacular sightings --intermittent punctuations of bright rapidlymoving points of light. Because such events are not reported, we conclude that this class of object does not exist in detectable numbers.

A search for small comets with the Naval Space Command radar

“…We have conducted a search for small comets with the NAVSPASUR radar. The use of a radar to detect small comets avoids the controversy surrounding instrumental effects for the far ultraviolet detections [Parks et al 1997[Parks et al , 1998] and complements searches in the visible region of the spectrum [Rizk and Dessler, 1997;Harris and Scotti, 1998]. In order to verify that the radar can detect small comets, we carried out first-principle calculations of the radar scattering cross section for an idealized small-comet model consisting of a spherical, pure water snow core of density 0.02 g cm-3 (a lower limit assuming a total mass of 2 x 107 g and a diameter slightly larger than 10 m) and a thin carbon mantle, as proposed by Frank et al [1986b] and Frank and Sigwarth [1993].…”

“…The principal features of the hypothesized small comets as given by Sigwarth [1993, 1997a] are a globally the POLAR satellite, launched in February 1996. Following these reports, new criticism of the small-comet hypothesis has appeared, principally in two areas: concern about potential instrumental and algorithmic artifacts [Parks et al, 1997[Parks et al, , 1998Mozer et al, 1998;McFadden et al, 1998] and unacceptable geophysical consequences [Grier and McEwen, 1997;Swindle and Kring, 1997;Rizk and Dessler, 1997] (also see the special session "Very Small Comets" [Eos Trans. AGU, 79(17), Spring Meet.…”