Micrometeorites and Early Solar System Processes

Abstract

The constraint of grain sizes. The discussion presented in the last section suggests that Antarctic micrometeorites would dominantly originate from comets. However, they contain refractory inclusions made of refractory oxides (Fig. 46), abbreviated as CAIs (see Sect. 6.2), which can only be formed at the highest temperatures (T ≥ 1800 K) close to the early Sun. They are at least 10 times larger than the very small inclusions of refractory oxides (sizes of about 0.1–1 μm) observed in the most fine-grained SMMs belonging to the group of the chondritic–porous aggregates (see Zinner, 2004). In contrast, micrometeorite CAIs are smaller than those observed in CM-type HCCs (Gounelle et al., 2001), which are in turn about 10 times smaller than those observed in the “dry” carbonaceous chondrites (including the CV, CO and CK types), where they can reach a size of about 1 cm.