Expected characteristics of cometary meteorites

Abstract

Recent developments in our understanding of comets provide insights into the topic of cometary meteorites. These developments include the identification of comet-asteroid transition objects (such as 4015 Wilson-Harrington and 3200 Phaethon), information on the composition of cometary solids, and new ideas on the collisional history of Jupiter-family comets. In this work, we revisit this question, and we conclude that comets do indeed yield macroscopic meteorites, which either have not been found or have not been recognized. We also consider the expected characteristics of cometary meteorites, with an emphasis on those that may help identify and differentiate them from other types of meteorites. If cometary meteorites have preserved the main characteristics of cometary dust, the mineralogy would be dominated by highly unequilibrated anhydrous silicates, and the chemistry would be nearly chondritic but with a high abundance of C and N. On the other hand, if an unknown process produced extensive aqueous alteration in the material that formed cometary meteorites, they would resemble (or could even be) CI carbonaceous chondrites. We do not expect cometary meteorites to have chondrules. So far, no single meteorite looks unequivocally cometary. However, we have identified xenoliths in ordinary chondrite regolith breccias that meet most of our criteria for a cometary origin and deserve further study.