المعرفة

حبيبات قبل شمسية

(تم التحويل من غبار نجمي)

الحبيبات قبل الشمسية Presolar grains، هي مادة صلبة نمية على هيئة حبيبات صلبة دقيقة نشأت قبل تشكل الشمس. تشكلت حبيبات الغبار النجمي نتيجة تدفق وتبريد الغازات من النجوم قبل الشمسية المبكرة.

صاروخ بوينگ دلتا 2 حاملاً ستاردست منتظراً الإقلاع. اقتربت المركبة ستاردست من المذنب وايلد-2 في يناير 2004 وقامت أيضاً بجمع غبار نجمي يحتوي على حبيبات نجمية قبل شمسية.

stellar nucleosynthesis that took place within each presolar star gives to each granule an isotopic composition unique to that parent star, which differs from the isotopic composition of our solar system's matter as well as from the galactic average. These isotopic signatures often fingerprint very specific astrophysical nuclear processes[1] that took place within the parent star and prove their presolar origin.[2][3]

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المصطلح

التاريخ

في المذنبات

الخصائص

Presolar grains are investigated using scanning or transmission electron microscopes (SEM/TEM), and mass spectrometric methods (noble gas mass spectrometry, resonance ionization mass spectrometry (RIMS), secondary ion mass spectrometry (SIMS, NanoSIMS)). Presolar grains that consist of diamonds are only a few nanometers in size and are, therefore, called nanodiamonds. Because of their small size, nanodiamonds are hard to investigate and, although they are among the first presolar grains discovered, relatively little is known about them. The typical sizes of other presolar grains are in the range of micrometers.

Presolar grains consisting of the following minerals have so far been identified:

  • diamond (C) nanometer-sized grains (~2.6 nanometres (1.0×10−7 in) diameter)[4] possibly formed by vapor deposition[5]
  • graphite (C) particles and anions,[6] some with unlayered graphene cores[7]
  • silicon carbide (SiC) submicrometer to micrometer sized grains. Presolar SiC occurs as single-polytype grains or polytype intergrowths. The atomic structures observed contain the two lowest order polytypes: hexagonal 2H and cubic 3C (with varying degrees of stacking fault disorder) as well as 1-dimensionally disordered SiC grains.[8] In comparison, terrestrial laboratory synthesized SiC is known to form over a hundred different polytypes.
  • titanium carbide (TiC) and other carbides within C and SiC grains[9]
  • silicon nitride (Si3N4)
  • corundum (Al2O3)[10]
  • spinel (MgAl2O4)[11]
  • hibonite ((Ca,Ce)(Al,Ti,Mg)12O19)[12]
  • titanium oxide (TiO2)
  • silicate minerals (olivine and pyroxene)

معلومات عن تطور النجوم

انظر أيضاً

المصادر

  1. ^ Ernst Zinner (1998) Stellar nucleosynthesis and the isotopic composition of presolar grains from primitive meteorites, Annual Review of Earth and Planetary Sciences 26:147-188.
  2. ^ T. J. Bernatowicz and R. M Walker (1997) Ancient stardust in the laboratory, Physics Today 50:1212, 26-32
  3. ^ D.D. Clayton and L.R. Nittler, Astrophysics with presolar stardust, Annual Review of Astronomy and Astrophysics 42, 39-78 (2004)
  4. ^ P. Fraundorf, G. Fraundorf, T. Bernatowicz, R. Lewis, and M. Tang (1989) Ultramicroscopy 27:401–412.
  5. ^ T. L. Daulton, D. D. Eisenhour, T. J. Bernatowicz, R. S. Lewis and P. R. Buseck (1996) Genesis of presolar diamonds: Comparative high-resolution transmission electron microscopy study of meteoritic and terrestrial nano-diamonds, Geochimica et Cosmochimica Acta 60:23, 4853-4872
  6. ^ T. Bernatowicz, R. Cowsik, P. C. Gibbons, K. Lodders, B. Fegley Jr., S. Amari and R. S. Lewis (1996) Constraints on stellar grain formation from presolar graphite in the Murchison meteorite, Ap. J. 472:760-782
  7. ^ P. Fraundorf and M. Wackenhut (2002) The core structure of pre-solar graphite anions, Ap. J. Lett. 578:2, L153-156
  8. ^ Daulton, T.; Bernatowicz, T. J.; Lewis, R. S.; Messenger, S.; Stadermann, F. J.; Amari, S. (June 2002). "Polytype distribution in circumstellar silicon carbide". Science. 296 (5574): 1852–1855. Bibcode:2002Sci...296.1852D. doi:10.1126/science.1071136. PMID 12052956.
  9. ^ T. Bernatowicz, S. Amari, E. Zinner, & R. Lewis (1991) Presolar grains within presolar grains, Ap J Lett, 373:L73
  10. ^ Hutcheon, I. D.; Huss, G. R.; Fahey, A. J.; Wasserberg, G. J. (1994). "Extreme Mg-26 and O-17 enrichments in an Orgueil corundum: Identification of a presolar oxide grain" (PDF). Astrophysical Journal Letters. 425 (2): L97–L100. Bibcode:1994ApJ...425L..97H. doi:10.1086/187319.
  11. ^ E. Zinner, S. Amari, R. Guinness, A. Nguyen, F. J. Stadermann, R. M. Walker and R. S. Lewis (2003) Presolar spinel grains from the Murray and Murchison carbonaceous chondrites, Geochimica et Cosmochimica Acta 67:24, 5083-5095
  12. ^ T. R. Ireland (1990) Presolar isotopic and chemical signatures in hibonite-bearing refractory inclusions from the Murchison carbonaceous chondrite, Geochmica et Cosmochimica Acta 54:3219-3237

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