Mathematics – Logic
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27r.243k&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 243
Mathematics
Logic
5
Scientific paper
Interplanetary Dust Particles (IDPs) collected in the atmosphere are a very special source of information about solar system objects like asteroids and comets. Suggested IDP properties indicative of their origins include amounts of 4He and 4He release temperatures (Nier and Schlutter 1990, 1992), solar flare track densities (Sandford and Bradley 1989), and trace element abundances (Flynn et al. 1992). Recently Flynn et al. (1992) suggested that Zn depletions of IDPs are indicative of heating in the atmosphere. On the average, asteroidal particles experience less heating than cometary particles (Flynn 1989). Nier and Schlutter (1992) showed that 4He release temperatures of individual IDPs vary from 420 C up to more than 800 C. Presently it is not clear if variations of 4He contents are a result of the original mineral compositions, and therefore source of individual IDPs, or if they are mainly affected by atmospheric entry heating. We studied the mineralogy of IDPs having variable amounts of 4He. Some of the particles were analyzed by SXRF for volatile trace elements. The particles in Table 1 are ordered according to their amount of 4He. High 4He contents (>11.0 x 1O^-11 cm^3) are found among particles characterized by their porous texture and occurrence of unequilibrated mineral phases. Particles of this group contain abundant glass, solar flare tracks are preserved and have chondritic Zn abundances. Among the 13 particles having low 4He contents six particles contain magnetite crystals that formed by atmospheric entry heating. Three magnetite-bearing particles are low in Zn. Though high in Zn, due to a Zn-bearing iron-sulfide in the center, L2005C19 is a heated particle. L2005A8 is texturally similar to other heated particles, but magnetites were so far not identified. According to Rietmeijer and Mackinnon (1985), particle W7029*A was not heated above 315 C and this explains its chondritic Zn level at a low amount of 4He. Three hydrated IDPs have low 4He contents. The presence of smectite and tochilinite in these particles limits their heating temperatures to 500-700 C and 250 C, respectively, consistent with the high Zn abundance of L2005D30. Two anhydrous equilibrated particles have low 4He (4.5 and 1.1 x 10^-11 cm^3), but do not show mineralogical evidences of heating in the Earth's atmosphere. Our observations indicate that agglutinate-like IDPs have higher amounts of 4He due to their exposure to the solar wind as asteroidal regolith particles. Hydrated particles, as well as the equilibrated particles, might be pieces of asteroidal subsurface lithologies, which were partly shielded from solar wind particles. IDPs heated during atmospheric entry are characterized by abundant magnetites coupled with Zn-depletion and low amounts of 4He. References: Flynn G.J. (1989) Icarus 77, 287. Flynn G.J., Sutton S.R., Thomas K.L., Keller L.P., and Klock W. (1992) Lunar Planet. Sci. (abstract) 23, 375. Nier A.O. and Schlutter D.J. (1990) Meteoritics 25, 263. Nier A.O. and Schlutter D.J. (1992) Meteoritics, submitted. Rietmeijer F.J.M. and Mackinnon I.D.R. (1985) Nature 316, 6022. Sandford S.A. and Bradley J.P. (1989) Icarus 82, 146.
Flynn George James
Klöck W.
Nier Alfred O.
Sutton Richard S.
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