Surface modification of olivine by H⁺ and He⁺ bombardment

Abstract

Abstract. Laboratory simulations of solar wind irradiation of olivine, a constituent of ordinary chondritic meteorites and S-type asteroids, show a dramatic chemical reduction of surface iron and, to a lesser extent, silicon. Earth's atmosphere oxidizes any reduced iron instantaneously, whereas irradiated material on the surface of an asteroid would remain reduced. Changes in optical reflectance, due to metallization of the surface, provide a possible explanation for differences in the near-infrared spectra of ordinary chondrite meteorites and their likely parent bodies, the S(IV) asteroids. IntroductionIn an equilibrium condensation model of the formation of the solar system [Grossman, 1972], the mineral phases present in ordinary chondrite meteorites, olivine, pyroxene, plagioclase, and metallic iron, are formed at primordial temperatures consistent with the inner edge of the asteroid belt; therefore one might expect to find ordinary chondritic parent bodies within this region. However, the spectral reflectance of S-type asteroids has a redder slope and weaker 1.

Structural processing of enstatite by ion bombardment

“…This result finds support by earlier experiments (Wang et al 1998;Wang & Ewing 1992;Dukes et al 1999). Apparently, such chemical changes are very sensitive to the energy range, as the experiments by Demyk et al (2001) and Bradley (1994) show, who found chemical effects by their experiments with ions of an energy range between 4 and 10 keV.…”

“…Apparently, such chemical changes are very sensitive to the energy range, as the experiments by Demyk et al (2001) and Bradley (1994) show, who found chemical effects by their experiments with ions of an energy range between 4 and 10 keV. The process of selective sputtering is strongly depending on the energy of the ions but, probably, also on the experimental conditions (Dukes et al 1999). A compositional processing of enstatite by interaction of interstellar cosmic rays should only occur at very low energies.…”

“…The authors did not report changes in the Mg/Si ratio. Bradley (1994) investigated the amorphization process of olivines with 20 keV H + , whereas Dukes (1999) simulated a solar wind bombardment of olivines with 1 keV H + and 4 keV He + ions. The latter author described chemical changes due to reduction processes of the Fe 2+ and a small amount of Si 4+ ions to the neutral elements, but no changes of the olivine stoichiometry.…”

Simulation of space weathering of planet-forming materials: Nanosecond pulse laser irradiation and proton implantation on olivine and pyroxene samples

“…Recently Dukes et al (1999) performed KeV range proton and helium bombardment on olivine surface. The total particle doses in their experiments are from 10 16 to 10 18 cm −2 , somewhat larger than that of our experiments.…”

The Role of Solar Wind in the Formation of Hydroxyl on Airless Silicate Bodies in Space

“…Irradiation causes chemical changes in the irradiated region of silicates [Dukes et al, 1999;Daviosne et al, 2008] as well as enhances the reactivity of the surface [Lanford and Burman, 1983;Cantando et al, 2008] including the potential to form OH bonds [Gruen et al, 1976] and increases diffusivity [Dienes and Damask, 1958]. Samples returned during the Apollo era have been in storage for over 40 years, and even though they have been stored in a nitrogen purged atmosphere, trace amounts of water vapor and hydrogen could diffuse into the materials.…”