Computer Science
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....11976l&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #11976
Computer Science
Scientific paper
Mineral phases in the interplanetary medium are subjected to the solar wind irradiation. Irradiation induces fractional volatilization of chemical elements in silicates; if large scale directional flow occurs, such as predicted by numerous models in the early solar system, then large scale chemical fractionnations occur. Electron irradiation experiments were performed using a 30 keV electron beam on single crystals of olivine in a scanning electron microscope (SEM) and in an electron microprobe (EMP) (Lemelle et al. 2003). Structural damage is caused to the irradiated surface of the iron-bearing olivines. The irradiated areas comprise spherules with sizes of hundreds of nanometers and micrometer-sized holes observed on Focused Ion Beam cuts. In the immediate vicinities of the irradiated areas, droplets with sizes of tens of nanometers and tracks are observed. With increasing total charge, the hundreds of nanometer-sized spherules become larger and more irregular in shape. The size and shape of the nanometer-sized droplets remain almost constant, but their surface density increases (in cm-2). Compared to the initial olivine, irradiated areas are slightly enriched in MgO, whereas the deposits are enriched in SiO_2. This destabilization of olivine results most probably from electrostatic discharges leading to the breakdown of the dielectric lattice. The possibility that such processes could be responsible for significant space weathering of interplanetary dust particles and regoliths of planetary surfaces should be taken into account. In the interplanetary medium, 10 keV-range electrons are carried by the solar wind, whereas at 1 AU from the Sun, the lifetime of cometary dust and the exposure time of lunar regolith are, at least, 10 to 100 times greater than the duration required to accumulate the damaging electronic doses applied in this study. Moreover, the comparison of the microstructures of samples irradiated in the present study with features of lunar regolith grains reveals several chemical and structural similarities. Interestingly, experiments carried out in transmission EM, with 100 keV-range electrons (Carrez et al. 2002) showed different mechanism of destabilization and chemical fractionation elemental loss from the silicate matrix. Lemelle et al. (2003) to be printed in Geochimica Cosmochimica Acta. Carrez P., Leroux H., Cordier P. and Guyot F. (2001) Philos. Mag. A 81, 2823-2840.
Beaunier L.
Borensztajn S.
Fialin M.
Guyot Francois
Lemelle Laurence
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