REPORT OF O ISOTOPIC COMPOSITIONS OF TWOITOKAWA PARTICLES FROM ROOM B AND
MEASUREMENT
PLAN
FOR
IN-SITU
3DDISTRIBUTION ANALYSIS OF SOLAR WIND NOBLEGASES ON SURFACE OF ITOKAWA PARTICLES.
H. Yurimoto1 , S. Itoh2 and K. Bajo2. 1Hokkaido University. Email: yuri@ep.sci.hokudai.ac.jp. 2Kyoto University.
O isotopic composition of Room B particles: Oxygenisotopic composition is one of finger prints of asteroids linking
meteorite types which are beliaved as fragments of asteroids. All
Itokawa particles from Room A show a constant oxygen isotope
anormaly corresponding to LL chondrites which are one chemical
type of ordinaly chondrites and most frequent fall among
meteorites [1]. Because asteroid Itokawa is a rubble-pile body, it
is not obvious whether the body is constructed by single
chondrite group. Therefore, oxygen isotopic measurement fromdifferent sites of the asteroid is important to analyze rubble-pilebody structure. We measureed two itokawa particles collectedfrom Room B, which are collected from the first tauch-down siteof Hayabusa whereas Room A particles from the second tauchdown site. The paaticles named RB-QD04-0006 and -0025 are
20-30µm in size and mainly consist of olivine and plagioclase,and low-Ca pyroxene, respectively. The chemical compositionsof minerals are similar to the corresponding minerals from RoomA samples. The oxygen isotopic compositions are distributed inequiribrium between minerals and show Δ17O=0.83-1.47, which
are the same signature observed in Room A samples. Therefore,
rubble-pile structure of Itokawa seems to be monomict.
In-situ 3-D analysis of noble gases from surface ofItokawa particles: A unique feature of Itakawa particles are
exposed intact surfaces to violent space environments. A TEM
study demonstrate that solar wind particles were implanted in thesurface thin layer of Itokawa particle [2]. Solar noble gasses aredetected from individual particles [3]. However, spatial
distribution of solar noble gases has not been determined everfrom natural samples. In order to determine nano-scale 3-D
distribution of solar wind particles in astromaterials, we develop
a novel mass spectrometer using tunneling ionization. The
development was started from 2004 at one year after launching ofHayabusa spacecraft, but was independently from the Hayabusa
mission [4]. Recently, we have newly developed new generation
sputtered neutral mass spectrometry capable to detect tens ppma
He from ~50 nm area on solid surface [5]. This project will be
figured out how distribute He (and other noble gases and H) in
the surface layer of Itokawa particles with tens nm resolution. If
this distribution is clarified, we can apply atomic mechanisms insolid clarified by mineralogy and crystallography, such asdiffusion, partitioning, etc., to the noble gas cosmochemistry. Asa result, behavior of noble gas in solid can be used to describe
space environments as the same manner of trace element
behavior for terrestrial environmental research. Therefore, thisproject is the first step to pioneer a new research field of noble
gas mineralogy or noble gas astromineralogy.
References: [1] Yurimoto H et al. 2011. Science 333:1116–1119. [2] Noguchi T et al. 2011. Science 333:1121–1125. [3]Nagao K et al. 2011. Science 333:1128–1131. [4] Ishihara M et al.
2010, Surf. Interface Anal. 42: 1598-1602. [5] Ebata S et al. 2012,Surf. Interface Anal. 44: 635-640.