SPACE WEATHERING EFFECTS AND THE CASE OF(162173) 1999 JU3.
M.A. Barucci1 and C. Lantz1. 1LESIA – Paris Observatory,France. E-mail: antonella.barucci@obspm.fr
Introduction: The exposure of airless bodies to solar ion
irradiations, micrometeorite bombardments, UV radiations leads
to surface alterations affecting the interpretation of composition
made from spectra. But these space weathering effects have been
widely studied for the S-type asteroids using laboratory
simulations on analog oridinary chondrites [1] and have been
confirmed thanks to space missions like NEAR-Shoemaker on
Eros [2]. There are a darkening and a reddening of the spectra
and mitigation of the absorption bands. A strong confirmation has
also been given by the first asteroid sample return mission
Hayabusa onto S-type Itokawa [3, 4]. Very little is known forspace weathering on primitive dark asteroids [5]. Hayabusa-2
mission will represent a great opportunity to discover in situ theeffects of this alteration on a primitive surface with the target
asteroid (162173) 1999 JU3, classified as a C-type and associatedto Murchison meteorite [6, 7].
Results: To investigate the possible space weathering effecton carbonaceous asteroids spectral signatures, we started with thestudy of CM chondrites compared to parent bodies Ch/Cgh-type
asteroids [5]. The differences between spectra of particulate
samples of the meteorites (assumed to represent asteroid
subsurface material) and spectra of the regolith of asteroids havebeen associated to asteroid surface processes. Our results
indicated a blueing effect on the spectra associated to space
weathering, as predicted by previous studies on organics [8, 9].
To better understand this alteration process on dark primitive
material and to support the choice of sampling site for Hayabusa2 mission, we are conducting in parallel laboratory simulations
on primitive meteoritic analogs. We have already done
irradiations on the Allende [10] and Murchison meteorites [11]exposed to 40keV He+ and Ar+ ions using fluences up to 3.1016
ions/cm2 as a simulation of solar wind. If a reddening/darkeningof Vis-NIR reflectance spectra is confirmed on Allende [12], weobserve negligible spectral variations in the case of Murchisonwith respect to viewing geometry or sample preparation. Other
different carbonaceous chondrites (CI, CK, CM, CO, CV) will beirradiated and analyzed to decypher the contradictory space
weathering studies of the darkest asteroids and with the aim tobuild a preliminary model of space weathering on low-albedo
asteroid. Our preliminary results will be presented and discussed.
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1617-1637 [3] Hiroi et al. 2006 Nature 443 pp. 56-58 [4]Noguchi et al. 2011 Science 333 pp. 1121-1125 [5] Lantz et al.
2013 Astronomy & Astrophysics 554 A138 [6] Takagi et al.
2011 American Geophysical Union Fall Meeting abstract #P21E04 [7] Sugita et al. 2013 44th Lunar & Planetary Science
Conference p. 2591 [8] Moroz et al. 2004 Icarus 170 pp. 214-228[9] Nesvorny et al. 2005 Icarus 173 pp. 132-152 [10] Brunetto etal. 2014 Icarus 237 pp. 278-292 [11] Lantz et al. in prep. [12]Lazzarin et al. 2006 The Astrophysical Journal 647 pp. 179-182