In a coming issue, Astronomy & Astrophysics presents new laboratory results that provide some important clues to the possible origins of exotic mineral grains in interplanetary dust. Studying interplanetary grains is currently a hot topic within the framework of the NASA Stardust mission, which recently brought back some samples of these grains. They are among the most primitive material ever collected. Their study will lead to a better understanding of the formation and evolution of our Solar System.
Fig. 1. Image of a GEMS in an interplanetary dust particle. Copyright: NASA
Fig. 2. Iron grain embedded in silicate glass.
Through dedicated laboratory experiments aimed at simulating the possible evolution of cosmic materials in space, C. Davoisne and her colleagues explored the origin of the so-called GEMS (glass with embedded metal and sulphides). GEMS is a major component of the primitive interplanetary dust particles (IDPs). They are a few 100 nm in size and are composed of a silicate glass that includes small, rounded grains of iron/nickel and metal sulphide (Figure 1). A small fraction of the GEMS (less than 5%) have presolar composition and could therefore have an interstellar origin. The remainder have solar composition and may have been formed or processed in the early Solar System. The varied compositions of the GEMS make it difficult to arrive at a consensus regarding their origin and formation process.
The team first postulates that the GEMS precursors originated in the interstellar medium and were progressively heated in the protosolar nebula. To test the validity of this hypothesis a joint experimental project involving two French laboratories, the Laboratoire de Structure et Propriétés de l’Etat Solide (LSPES) in Lille and the Institut d’Astrophysique Spatiale (IAS) in Orsay, was set up. Z. Djouadi, at the IAS, heated various amorphous samples of olivine ((Mg,Fe)2SiO4) under high vacuum and at temperatures ranging from 500 to 750°C. After heating, the samples show microstructures that closely resemble those of the GEMS, with rounded iron nanograins that are seen to be embedded in a silicate glass (Figure 2).
Jennifer Martin | alfa
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