Mechanisms of grain formation, post‐accretional alteration, and likely parent body environments of interplanetary dust particles (IDPS)

The fine‐scale mineralogy and petrography of the various classes of IDPs provide information about grain‐forming reactions, as well as insight into the nature of IDP parent body environments. Many anhydrous, pyroxene IDPs are (solar flare) track‐rich, have undergone negligible post‐accretional alteration, and have preserved mineralogical evidence of primoridal gas‐phase reactions. Most anhydrous, olivine IDPs appear to have undergone post‐accretional heating and, since only a few track‐rich olivine IDPs have been identified, it is possible the heating occurred during atmospheric entry. Infrared (IR) transmission and visible (VIS) reflectance data from track‐rich anhydrous IDPs suggest that some of them were derived from outer asteroids or comets. Hydrated, layer‐silicate IDPs have undergone significant post‐accretional aqueous alteration. Three layer silicate IDPs have now been linked directly to carbonaceous chondrite petrogenisis and a (main belt) asteroid origin, and it is possible that most of them are from hydrous asteroids. Several layer silicate IDPs exhibit (VIS) spectral reflectivities similar to main‐belt C asteroids.