The genetic relationship between hydrous and anhydrous interplanetary dust particles

It is a fundamental goal of interplanetary dust particle (IDP) research to determine the sources and histories of these primitive extraterrestrial materials. Chondritic IDPs have been divided into anhydrous and hydrous varieties, with sub-classification being made on the grounds of the dominant anhydrous (olivine or pyroxene) or hydrous (smectite or serpentine) present. The presumption is that hydrated IDPs experienced aqueous alteration on parent bodies (hydrous asteroids or possibly comets); we wish to discover whether the anhydrous IDPs were the initial raw materials for these reactions. We report here analyses of olivines and pyroxenes from 22 large (>15 um) chondritic IDPs: 18 anhydrous and 4 hydrous; olivines and pyroxenes are scarce in most hydrous IDPs, when present at all Finally, we compare anhydrous to hydrous IDPs, and both to chondritic meteorites. Figure 1 shows our results for this study. We find there to exist no significant difference in the compositions of olivines from olivine vs. pyroxene dominated IDPs, which are therefore plotted together (in contrast to our preliminary results for a smaller data set).