Evolution of Dust and Water Ice in Cometary Comae by Radiative Torques
  Comets provide unique information about the physical and chemical properties
of the environment in which the Solar system was formed. Understanding how
cometary dust and ice evolve under the effect of sunlight is essential for
constraining nuclear structure and triggering mechanism of comet activity. In
this paper, we first study rotational disruption of dust grains lifted by
outgassing from comet nuclei by radiative torques (RATs). We find that
composite grains could be rapidly disrupted into small fragments by the
Radiative Torque Disruption (RATD) mechanism. We then study rotational
desorption of ice grains by RATs and find that icy grains could be desorbed
from large heliocentric distances, beyond the sublimation radius of water at
$R_{\rm sub}(\H_{2}\O)\sim 3\AU$. We also calculate the production rate of
water vapor versus the heliocentric distance of comets due to rotational
desorption. Our results could explain the variation of dust properties and the
presence of small grains frequently observed from cometary comae. Finally, we
suggest that the activity of distant comets could be triggered by rotational
disruption of grains and desorption of water ice grains at large heliocentric
distances.
