  Primitive meteorites are dominated by millimeter-size silicate spherules
called chondrules. The nature of the high-temperature events that produced them
in the early solar system remains enigmatic. Beside their thermal history, one
important clue is provided by their size which shows remarkably little
variation (less than a factor of 6 for the mean chondrule radius of most
chondrites) despite the extensive range of ages and heliocentric distances
sampled. It is however unclear whether chondrule size is due to the chondrule
melting process itself, or has been simply inherited from the precursor
material, or yet results from some sorting process. I examine these different
possibilities in terms of their analytical size predictions. Unless the
chondrule-forming "window" was very narrow, radial sorting can be excluded as
size-determining processes because of the large variations it would predict.
Molten planetesimal collision or impact melting models, which derive chondrules
from the fragmentation of larger melt bodies, would likewise predict too much
size variability by themselves; more generally any size modification during
chondrule formation is limited in extent by evidence from compound chondrules
and the considerable compositional variability of chondrules. Turbulent
concentration would predict a low size variability but lack of evidence of any
accretion bias in carbonaceous chondrites may be difficult to reconcile with
any form of local sorting upon agglomeration. Growth by sticking (especially if
bouncing-limited) of aggregates as chondrule precursors would yield limited
variations of their final radius in space and time, and would be consistent
with the relatively similar size of other chondrite components such as
refractory inclusions. This suggests that the chondrule-melting process(es)
simply melted such nebular aggregates with little modification of mass.
