  About 4-5% of chondrules are compound: two separate chondrules stuck
together. This is commonly believed to be the result of the two component
chondrules having collided shortly after forming, while still molten. This
allows high velocity impacts to result in sticking. However, at T ~ 1100K, the
temperature below which chondrules collide as solids (and hence usually
bounce), coalescence times for droplets of appropriate composition are measured
in tens of seconds. Even at 1025K, at which temperature theory predicts that
the chondrules must have collided extremely slowly to have stuck together, the
coalescence time scale is still less than an hour. These coalescence time
scales are too short for the collision of molten chondrules to explain the
observed frequency of compound chondrules. We suggest instead a scenario where
chondrules stuck together in slow collisions while fully solid; and the
resulting chondrule pair was subsequently briefly heated to a temperature in
the range of 900-1025K. In that temperature window the coalescence time is
finite but long, covering a span of hours to a decade. This is particularly
interesting because those temperatures are precisely the critical window for
thermally ionized MRI activity, so compound chondrules provide a possible probe
into that vital regime.
