  The formation of chondrules is one of the oldest unsolved mysteries in
meteoritics and planet formation. Recently an old idea has been revived: the
idea that chondrules form as a result of collisions between planetesimals in
which the ejected molten material forms small droplets which solidify to become
chondrules. Pre-melting of the planetesimals by radioactive decay of 26Al would
help producing sprays of melt even at relatively low impact velocity. In this
paper we study the radiative cooling of a ballistically expanding spherical
cloud of chondrule droplets ejected from the impact site. We present results
from a numerical radiative transfer models as well as analytic approximate
solutions. We find that the temperature after the start of the expansion of the
cloud remains constant for a time t_cool and then drops with time t
approximately as T ~ T_0[(3/5)t/t_cool+ 2/5]^(-5/3) for t>t_cool. The time at
which this temperature drop starts t_cool depends via an analytical formula on
the mass of the cloud, the expansion velocity and the size of the chondrule.
During the early isothermal expansion phase the density is still so high that
we expect the vapor of volatile elements to saturate so that no large volatile
losses are expected.
