  We revisit the computation of a "snow line" in a passive protoplanetary disk
during the stage of planetesimal formation. We examine how shadowing and
illumination in the vicinity of a planet affects where in the disk ice can
form, making use of our method for calculating radiative transfer on disk
perturbations with some improvements on the model. We adopt a model for the
unperturbed disk structure that is more consistent with observations and use
opacities for reprocessed dust instead of interstellar medium dust. We use the
improved disk model to calculate the temperature variation for a range of
planet masses and distances and find that planets at the gap-opening threshold
can induce temperature variations of up to +/-30%. Temperature variations this
significant may have ramifications for planetary accretion rates and migration
rates. We discuss in particular the effect of temperature variations near the
sublimation point of water, since the formation of ice can enhance the
accretion rate of disk material onto a planet. Shadowing effects can cool the
disk enough that ice will form closer to the star than previously expected,
effectively moving the snow line inward.
