1I/`Oumuamua As Debris of Dwarf Interstellar Comet That Disintegrated Before Perihelion

Abstract

Intrinsically faint comets in nearly-parabolic orbits with perihelion distances much smaller than 1 AU exhibit strong propensity for suddenly disintegrating at a time not long before perihelion, as shown by Bortle (1991). Evidence from available observations of such comets suggests that the disintegration event usually begins with an outburst and that the debris is typically a massive cloud of dust grains that survives over a limited period of time. Recent CCD observations revealed, however, that also surviving could be a sizable fragment, resembling a devolatilized aggregate of loosely-bound dust grains that may have exotic shape, peculiar rotational properties, and extremely high porosity, all acquired in the course of the disintegration event. Given that the brightness of 1I/`Oumuamua's parent could not possibly equal or exceed the Bortle survival limit, there are reasons to believe that it suffered the same fate as do the frail comets. The post-perihelion observations then do not refer to the object that was entering the inner Solar System in early 2017, as is tacitly assumed, but to its debris. Comparison with C/2017 S3 and C/2010 X1 suggests that, as a monstrous fluffy dust aggregate released in the recent explosive event, `Oumuamua should be of strongly irregular shape, tumbling, not outgassing, and subjected to effects of solar radiation pressure, consistent with observation. The unknown timing of the disintegration event may compromise studies of the parent's home stellar system. Limited search for possible images of the object to constrain the time of the (probably minor) outburst is recommended.