  One of the first stages of planet formation is the growth of small
planetesimals and their accumulation into large planetesimals and planetary
embryos. This early stage occurs much before the dispersal of most of the gas
from the protoplanetary disk. Due to their different aerodynamic properties,
planetesimals of different sizes/shapes experience different drag forces from
the gas at these stage. Such differential forces produce a wind-shearing effect
between close by, different size planetesimals. For any two planetesimals, a
wind-shearing radius can be considered, at which the differential acceleration
due to the wind becomes greater than the mutual gravitational pull between the
planetesimals. We find that the wind-shearing radius could be much smaller than
the gravitational shearing radius by the Sun (the Hill radius), i.e. during the
gas-phase of the disk wind-shearing could play a more important role than tidal
perturbations by the Sun. Here we study the wind-shearing radii for
planetesimal pairs of different sizes and compare it with gravitational
shearing (drag force vs. gravitational tidal forces). We then discuss the role
of wind-shearing for the stability and survival of binary planetesimals, and
provide stability criteria for binary planetesimals embedded in a gaseous disk.
