  The image of comet 2I/Borisov taken by the Hubble Space Telescope on October
12 shows a fan-like feature in the inner coma, which extends over a few
arcseconds from the nuclear condensation, its axis pointing a little west of
the north. It is proposed that this protrusion is a halo of centimeter-sized
and larger dust grains or pebbles released at low velocities from the nucleus
at large heliocentric distances (on the order of 10 AU or more) before
perihelion and subjected to very low radiation pressure accelerations. Unlike
potential microscopic dust from ongoing activity, this population of large
grains should show no silicate feature near 10 microns in the infrared and its
presence in 2I/Borisov can be tested observationally. The existence of material
of a similar size range in Oort Cloud comets with perihelia near or beyond the
snow line has long been documented by the characteristic orientation of their
tails.
