Chondrule formation by clumpy accretion onto the solar nebula

Chondrule textures and compositions appear to require rapid heating of precursor grain aggregates to temperatures in the range 1500 K to 2100 K, cooling times on the order of hours, and episodic and variable intensity events in order to produce chondrule rims and chemically distinct groups. Nebula shock waves have been proposed by Hood and Horanyi as a physical mechanism that may be capable of meeting the meteoritical constraints. Motivated by astronomical observations of the close environments of young stars, we suggest that the source of the nebula shock waves may be clumpy accretion onto the solar nebula - that is, episodic impacts onto the nebula by discrete cloud clumps with masses of at least 10(exp 22) g. If the cloud clumps are massive enough (10(exp 26) g), the resulting shockwave may be able to propagate to the midplane and process precursor aggregates residing in a dust sub-disk.