Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p42a..02n&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P42A-02
Physics
[6015] Planetary Sciences: Comets And Small Bodies / Dust
Scientific paper
Dust particles of the near-Earth asteroid 25143 Itokawa were successfully recovered by the spacecraft Hayabusa. After capsule landing in Australia on June 2010, sample curation work was carried out for 7 months at the curation facility of JAXA in Japan, so as to separate, identify and store the asteroidal samples. Currently ~1500 small (mostly smaller than 10 microns) and ~100 large (mostly 30-180 microns) particles were identified as samples from asteroid Itokawa. Curatorial processes are performed in a pure nitrogen atmosphere and therefore the asteroidal samples have never been exposed to atmosphere. Fifty-seven large particles were distributed to eight research groups in Japan for preliminary analysis. The period of the initial analysis will continue to the end of November 2011 and then some fractions of the sample particles will be transferred to NASA/JSC. From early 2012, Itokawa samples are planned to distribute to researchers in the world. The results of preliminary analysis of Itokawa dust particles uncover the origin and formation of the asteroid Itokawa itself and the evolution of the asteroid regolith. Compositions of olivine, pyroxenes, plagioclase, chromite and NiFe metals, and the modes of occurrence of these minerals in Itokawa dust particles are similar to thermally metamorphosed LL chondrites [1, 2]. Oxygen isotope analysis of silicates in the particles indicates that they have oxygen isotope ratios similar to LL or L equilibrated ordinary chondrites [3]. Neutron activation analysis of a single large olivine-rich particle indicates that it has Fe/Sc and Ni/Co ratios similar to chondrite [4]. These facts verify the spectroscopic observations performed from Earth [5] and by the Hayabusa Spacecraft [6] and also prove that ordinary chondrites are derived from S-type asteroids. STEM observations of particle surface suggest mechanisms for asteroidal space weathering: sulfur-bearing Fe-rich nanoparticles (npFe) in a very thin surface formed by vapor deposition and metallic npFe existing up to ~60 nm deep from the surfaces of ferromagnesian silicates formed by radiation induced reduction [7]. Noble gas analysis of individual Itokawa particles indicates that they are enriched in solar-wind noble gases acquired by repeated implantation [8]. 3D shape features of the particles suggest that the particles were formed by meteoroid impacts on the asteroid surface [2]. Any signs of the presence of organic materials have never been detected so far [9].
Abe Mitsuko
Ebihara Mitsuru
Fujimura Akio
Ishibashi Yoshinobu
Kawaguchi Jun'ichiro
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