  We assess whether chondrules, once-molten mm-sized spheres filling the oldest
meteorites, could have formed from super-km/s collisions between planetesimals
in the solar nebula. High-velocity collisions release hot and dense clouds of
silicate vapor which entrain and heat chondrule precursors. Thermal histories
of CB chondrules are reproduced for colliding bodies $\sim$10--100 km in
radius. The slower cooling rates of non-CB, porphyritic chondrules point to
colliders with radii $\gtrsim$ 500 km. How chondrules, collisionally dispersed
into the nebula, agglomerated into meteorite parent bodies remains a mystery.
The same orbital eccentricities and inclinations that enable energetic
collisions prevent planetesimals from re-accreting chondrules efficiently and
without damage; thus the sedimentary laminations of the CB/CH chondrite
Isheyevo are hard to explain by direct fallback of collisional ejecta. At the
same time, planetesimal surfaces may be littered with the shattered remains of
chondrules. The micron-sized igneous particles recovered from comet 81P/Wild-2
may have originated from in-situ collisions and subsequent accretion in the
proto-Kuiper belt, obviating the need to transport igneous solids across the
nebula. Asteroid sample returns from Hayabusa2 and OSIRIS-REx may similarly
contain chondrule fragments.
