Infrared Spectroscopy of Comet Wild-2 Samples Returned by the Stardust Mission.

Mathematics – Logic

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6008 Composition (1060), 6015 Dust, 6023 Comets: Dust Tails And Trails (6210), 6040 Origin And Evolution

Scientific paper

Comets are widely believed to be repositories of the building blocks of the solar system that include both presolar and early nebular matter. The nature of these organic and inorganic materials in comets is inferred through the analysis and interpretation of features in their infrared (IR) spectra, especially the mid- and far-IR parts of the spectrum where organic materials and minerals have diagnostic bands. With bonafide samples of a specific comet now returned by the Stardust mission, their detailed analysis provides a direct test of current hypotheses regarding the chemical and mineralogical composition of comets based largely on astronomical measurements, comet encounter missions and laboratory analyses of cometary IDPs. Indigenous organic matter from Comet Wild-2 was collected by the Stardust mission and survived capture. It is associated with discrete particles and as finely disseminated material within impact cavities in the aerogel collection medium. Fourier transform infrared (FTIR) measurements of extracted particles and in situ measurements from individual impact tracks show absorption features in the C-H stretching region that are consistent with long chain aliphatic hydrocarbons. Extracted terminal particles and some of the particles from the base of the impact cavity also show sharp features in mid- and far-IR spectra consistent with crystalline silicates, including enstatite, olivine and diopside. Amorphous silicates are also a major component of comet Wild-2 samples. Indeed, despite complications due to overlap with the aerogel Si-O feature, the majority of Wild-2 particles analyzed to date with IR spectroscopy are dominated by amorphous silicates, although the thermal effects of the particle collection are still being assessed. No FTIR evidence for hydrated silicates or carbonates has been observed to date in any of the extracted particles. The presence of the crystalline silicates in the Wild-2 samples indicates that it is not an assemblage of preserved interstellar silicates, but rather is a mixture of presolar and solar system materials.

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