Chondrule origins: Constraints from chondrule properties and cosmochemistry

The origin of chondrules is a problem for the ages. Yet even though a detailed formation mechanism remains elusive, the constraints on possible mechanisms become more stringent with each systematic examination of chondrules that involves a higher level of resolution. Constraints presented here are mainly based on studies of chondrules in unequilibrated ordinary chondrites because these have been studied much more than other primitive chondrites. These constraints are listed in six categories: the first four are constraints of chondrule origin and the last two reflect the constraints chondrule properties place on the ambient nebula.