P-rich compounds within the Ryugu sample collection: a perspective from joint
MicrOmega/Curation, the OU and Phase2 Kochi curation activities
1,2Pilorget, C.; 1Loizeau, D.; 3Ito, M., 1Bibring, J.-P.; 1Carter, J.; 1Le Pivert-Jolivet, T.; 1,4Riu, L.; 1Brunetto, R.; 3Tomioka, N.;
5
Uesugi, M.; 6Yamaguchi, A.; 6Imae, N.; 7,8Hatakeda, K.; 7Yogata, K; Y.; 1Baklouti, D.; 7,9Okada, T.; 7Yada, T.; 7,9Usui,T.;10Greenwood, R.; 11Liu, M., and the Ph2K team, the OU team and the MicrOmega Curation Team.
1IAS, Université Paris-Saclay, CNRS, France, 2Institut Universitaire de France, 3JAMSTEC, Kochi Inst. Core Sample
Research, 4ESAC, ESA, Madrid, Spain, 5JASRI, 6National Institute of Polar Research, 7Institute of Space and Astronautical
Science, Japan Aerospace Exploration Agency, 8Marine Works Japan, Ltd, 9University of Tokyo, Bunkyo, Tokyo 113-0033,Japan, 10Open U. UK, 11UCLA US
The JAXA Hayabusa2 mission has returned for the first time samples collected at the surface of a C-type asteroid, Ryugu[1,2]. They are now preserved at the Extraterrestrial Samples Curation Center of JAXA at ISAS in Sagamihara, Japan, where
they are submitted to a first round of non-destructive and non-invasive analyses, while maintained in a purely non-altering
environment since their collection [3]. Some of these grains have also been extracted to be further analyzed by - initially - 8
analytical teams, including Phase2 Kochi (Ph2K) curation [4,5], and later open to AOs.
The MicrOmega hyperspectral microscope operating in the near-infrared (NIR) range (0.99 – 3.65 µm) is performing themineralogical and molecular characterization of the samples present in the Curation Center, down to the scale of a few tens ofmicrometers [6]. By the end of September 2022, >375 individual grains (a few mm in diameter) and 25 sub-bulks (a few tensof mg each) have been analyzed with MicrOmega, in addition to the 6 initial bulks from chamber A and C. It offers a global
view on the Ryugu samples, preserved from any terrestrial contamination, and can be used to target specific grains and areas ofinterest with complementary techniques. In particular, while strong features at 2.7 µm – translating their OH-rich content - and3.4 µm – diagnostic of the presence of organics – dominate at a global scale, key distinctive signatures have been identified at
sub-mm scale [7,8,9,10]. Here we present the international collaborative curation work conducted with the Ph2K and the OU
on Ryugu samples and focused on the P-rich compounds.
Specific grains of interest/inclusions have been identified with MicrOmega within the Curation Facility, for having a brightaspect (reflectance of ~10-20%) coupled to a very peculiar spectrum in the NIR: a broad and deep band at ~3 µm, withadditional features, in particular a sharp band at ~2.7 µm shifted by ~10 nm compared to the one observed in the matrix [7].
Grains with such properties tend to occur as inclusions or loose grains with sizes up to a few hundreds of microns, similar tocarbonates observed by MicrOmega [8] but with a much lower occurrence. Such signatures have been identified in the C0209
sub-bulk delivered to the Ph2K team in April 2022. Grains presenting these properties have been manually extracted andanalyzed by SR-XRD at Spring-8 and then combined SEM/EDX at Kochi JAMSTEC, which revealed an enrichment in P, Oand Mg elements, possibly pointing towards Mg-phosphates as suggested by other observations on a few samples [11,12].
These grains and the C0209 sub-bulk were then re-analyzed by a MicrOmega unit present at IAS [13]. The results confirmed
the correlation between the IR signature and the P, O, Mg content detected by the EDX. Slight modifications of the IR spectrain the 2.7-3.0 µm range points towards a contact with the terrestrial atmosphere after the extraction of the grains from theCuration Center.
These results offer a new perspective on the characterization of the distribution and properties of such compounds over theentire collection. Further analysis of the grains is on-going to assess the possible couplings of the P-rich phases with othercompounds (minerals and/or organics) and their origin by H, O isotopic ratios.
References[1] Watanabe et al. (2019) Science 364 268-272. [2] Morota et al. (2020) Science 368 654-659. [3] Yada et al. (2022) Nat
Astron, 6, 214-220. [4] Ito et al. (2022) Nat Astron, [5] Liu et al. (2022) Nat Astron, [6] Bibring et al. (2017) Space Sci. Rev.
208, 401-412. [7] Pilorget et al. (2022) Nat Astron, 6, 221-225. [8] Loizeau et al. (2022) 53rd LPSC contrib. N°2017 [9] Carteret al. (2022) 53rd LPSC contrib. N°1495. [10] Bibring et al. (2022) this conference. [11] Nakamura et al. (2022) Proceedingsof the Japan Academy, Series B 98, 227–282. [12] Ma et al. (2022) MetSoc contrib. N°2695. [13] Loizeau et al. (2020)
Planetary and Space Science 193 article id. 105087.