AGGREGATE GROWTH AND INTERNAL STRUCTURES OF CHONDRITE PARENT BODIES FORMING FROM DENSE CLUMPS

Major components of chondrites are chondrules and matrix. Measurements of the volatile abundancein Semarkona chondrules suggest that chondrules formed in a dense clump that had a higher soliddensity than the gas density in the solar nebula. We investigate collisions between chondrules andmatrix in the surface region of dense clumps using fluffy aggregate growth models. Our simulationsshow that the collisional growth of aggregates composed of chondrules and matrix takes place in theclumps well before they experience gravitational collapse. The internal structure of chondrite parentbodies (CPBs) can be thereby determined by aggregate growth. We find that the aggregate growthgenerates two scales within CPBs. The first scale is involved with the small scale distribution ofchondrules and determined by the early growth stage, where chondrules accrete aggregates composedof matrix grains. This accretion can reproduce the thickness of the matrix layer around chondrulesfound in chondrites. The other scale is related to the large scale distribution of chondrules. Itsproperties (e.g., the abundance of chondrules and the overall size) depend on the gas motion withinthe clump, which is parameterized in this work. Our work thus suggests that the internal structureof CPBs may provide important clues about their formation conditions and mechanisms.