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The image of comet 2I/Borisov taken by the Hubble Space Telescope on October12 shows a fan-like feature in the inner coma, which extends over a fewarcseconds from the nuclear condensation, its axis pointing a little west ofthe north. It is proposed that this protrusion is a halo of centimeter-sizedand larger dust grains or pebbles released at low velocities from the nucleusat large heliocentric distances (on the order of 10 AU or more) beforeperihelion and subjected to very low radiation pressure accelerations. Unlikepotential microscopic dust from ongoing activity, this population of largegrains should show no silicate feature near 10 microns in the infrared and itspresence in 2I/Borisov can be tested observationally. The existence of materialof a similar size range in Oort Cloud comets with perihelia near or beyond thesnow line has long been documented by the characteristic orientation of theirtails.

Note on the HST Image of Comet 2I/Borisov Taken on 2019 October 12