Mathematics – Logic
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27q.268n&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 268
Mathematics
Logic
1
Scientific paper
We have reported on the extraction of helium and neon from individual IDPs by step-heating (1,2). The purpose of the study was to see if differences in release patterns existed which might shed light on the heating experienced by the particles in their deceleration during descent in the Earth's upper atmosphere. Flynn (3), as well as earlier investigators, has shown that dust particles originating in high perihelia comets or in asteroids would, in general, have less energy and hence are heated less than low perihelia comets. In a study of 20 particles (2) it was found that 12 contained an appreciable amount of helium, and this was released in the same general temperature range as found for typical lunar grains. Four particles contained considerably less helium, and this was released at a higher temperature. The remaining particles contained essentially no helium. In a more recent study, fragments of 12 IDPs were investigated as a part of a coordinated investigation. Other fragments of the same IDPs are being examined for elemental and mineralogical content by other investigators. In the new work (4) the gas is extracted by a succession of 5-second constant-power pulses of increasing power, closely resembling the heat pulses experienced by IDPs in their deceleration in the atmosphere (5). The amount of gas removed is studied as a function of the peak temperature reached in the individual pulses. Flynn and Sutton (6) and Flynn et al. (7), using Transmission Electron Microscopy (TEM) and Synchrotron X-ray Fluorescence (SXRF) for trace element analyses, have reported low zinc abundances in some IDPs. They believe the low abundance could be due to the loss of volatile elements through heating during the deceleration of the particles during atmospheric entry. In our present study, low amounts of helium were found in fragments which were parts of the same IDPs as the fragments for which low Zn concentrations were found (G. Flynn, private communication). Whether the effect is due to the general loss of volatile elements during atmospheric entry, or has a more basic explanation relating to the origin or earlier history of the IDPs, remains an open question until more investigations are undertaken. In a related study, we undertook the extraction of helium and neon by pulse-heating of individual lunar surface grains to see if differences in the relative rates of extraction of the two gases could be observed. While only a limited number of grains have been investigated to date, some systematic differences appeared to emerge. For example, in the case of pyroxene and glassy grains, the relative proportions of total helium and neon released at a given temperature, as the temperature of the pulses increased, was approximately the same. On the other hand, for plagioclase and ilmenite, a distinctly higher temperature was required to remove the neon than was the case for helium. Hence, if the low volatile content of IDPs is due to atmospheric deceleration heating, the interpretation of differences or similarities observed for helium and other volatile elements must take into account the mineral composition of the particles. References: (1) Nier, A.O. and Schlutter, D. J. (1991) Meteoritics 26, 379. (2) Nier, A. O. and Schlutter, D. J. (1992) Meteoritics 27, (in press). (3) Flynn, G. J. (1989) Icarus 77, 287-310. (4) Nier. A. O. and Schlutter, D. J. (1992) Lunar Planet. Sci. (abstract) 23, 991-992. (5) Love, S. G. and Brownlee, D. E. (1991) Icarus 89, 26-43. (6) Flynn, G. J. and Sutton, S. R. (1992) Proc. Lunar Planet. Sci. 22nd, 171-184. (7) Flynn, G. J., Sutton, S. R., Thomas, K. L., Keller, L. P., and Klock, W. (1992) Lunar Planet. Sci. (abstract) 23rd, 375-376.
Nier Alfred O.
Schlutter Dennis J.
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