Stardust glass: Indigenous and modified comet Wild 2 particles

Abstract

Does comet 81P/ Wild 2 have indigenous glass? Glass is used here to include all types of amorphous materials that could be either indigenous or modified comet Wild 2 grains, and all amorphous phases in chondritic aggregate interplanetary dust particles (IDPs). The answer is that it probably does, but very little is known of their compositions to allow a definitive answer to be given. There is no evidence among the collected comet dust for interstellar glass with embedded metals and sulfides. There is, however, ample evidence for melting of the smallest, sub-micrometer comet particles of nanometer-scale grains similar to those in the matrix of chondritic aggregate IDPs, including pyrrhotite. Massive patches of Mg-SiO, Al-SiO, or Ca-Si-O glass are incorporated in the familiar, vesicular Si-rich glass are melted Wild 2 silicates. Magnesiosilica glass has a deep metastable eutectic smectite-dehydroxylate composition. It indicates that very high temperatures well above the liquidus temperatures of forsterite were achieved very rapidly and were followed but ultrarapid quenching. This predictable and systematic response is not limited to Mg-silicates, and recognizing this phenomenon among massive glass will provide a means to complete the reconstruction of this comets original minerals, as well as constrain the physiochemical environment created during aerogel melting and evaporation.