The Astromineralogy of Interplanetary Dust Particles
Some chondritic interplanetary dust particles (IDPs) collected in the stratosphere are from comets. Because comets accreted at heliocentric distances beyond the giant planets, presolar grains or “astrominerals” with solar and non-solar isotopic compositio
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Abstract Some chondritic interplanetary dust particles (IDPs) collected in the stratosphere are from comets. Because comets accreted at heliocentric distances beyond the giant planets, presolar grains or “astrominerals” with solar and non-solar isotopic compositions are expected to be even more abundant in cometary IDPs than in primitive meteorites. Non-solar D/H and 15 N/14 N isotopic enrichments in chondritic IDPs are associated with a carbonaceous carrier. These H and N enrichments are attributed to extreme mass fractionation during chemical reactions in cold (10–100 K), dense interstellar molecular clouds. Enstatite (MgSiO3 ) and forsterite (Mg2 SiO4 ) crystals in IDPs are physically and compositionally similar to enstatite and forsterite grains detected around young and old stars by the Infrared Space Observatory (ISO), and large non-solar oxygen isotopic compositions recently measured in some IDP silicates establish that they are presolar silicates. The compositions, mineralogy, and optical properties of a class of grains in IDPs, known as GEMS, are consistent with those of interstellar “amorphous silicates”. Non-solar isotopic compositions measured in several GEMS confirm that they are interstellar silicate grains, one of the fundamental building blocks of solar systems. Submicrometer FeNi sulfide astrominerals like those found in IDPs may be responsible for a broad ∼23.5 µm feature observed around protostars and protoplanetary discs by ISO. The first sample of a known comet (81P/Wild 2) was returned to Earth in 2006 by the Stardust mission. Contrary to expectations, the “Wild 2” sample does not resemble “cometary” IDPs and it does not contain abundant astromaterials. Instead, this particular Kuiper Belt comet resembles chondritic meteorites from the asteroid belt, which reinforces the astrophysical significance of IDPs as perhaps the most cosmically primitive materials available for laboratory investigations.
J. Bradley (B) Lawrence Livermore National Laboratory, Institute of Geophysics and Planetary Physics, Livermore, CA 94551, USA e-mail: [email protected] Bradley, J.: The Astromineralogy of Interplanetary Dust Particles. Lect. Notes Phys. 815, 259–276 (2010) c Springer-Verlag Berlin Heidelberg 2010 DOI 10.1007/978-3-642-13259-9_6
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1 Introduction For the purposes of this chapter astrominerals are defined as those presolar mineral grains in primitive meteoritic materials that existed prior to collapse of the solar nebula. These grains may include preserved circumstellar grains, grains formed in supernovae outflows, grains formed or modified within the interstellar medium (ISM), including grains that were present in the presolar molecular cloud. They may have survived either because they were resistant to asteroidal parent body alteration processes within the inner solar system or because they were sequestered in small primitive bodies like comets at much larger heliocentric distances where postaccretional alteration processes were minimal or essentially non existent. Astrominerals ca
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