Ryugu’s volatiles investigated using stepped combustion and EGA methods
A.B. Verchovsky1, F. A. J. Abernethy1, M. Anand1, I. A. Franchi1, M. M. Grady1, R. C. Greenwood1 and M. Suttle1, M. Ito2,
N. Tomioka2, M. Uesugi3, A. Yamaguchi4, M. Kimura4, N. Imae4, N. Shirai5, T. Ohigashi6,7, M-C. Liu8, M. Abe9, T. Usui9.
1
The Open University, Milton Keynes, MK7 6AA, UK. 2KOCHI JAMSTEC, 3JASRI/SPring-8, 4NIPR, 5 Kanagawa Univ.,
6UVSOR IMS, 7PF/KEK 8LLNL, 9ISAS/JAXA, the Ph2K team, the MicrOmega team.

oCarbon yeild , ng/ CQMS signal, cps

Samples of the asteroid Ryugu collected by the Hayabusa 2 mission [e.g., 1-4] provide an excellent opportunity to undertakea comparative study for volatiles (e.g., H, C. N, S) measured in meteorites of similar type. This allows for a better understandingof the evolution of the meteoritic material during their transition through the atmosphere and residence on the surface of theEarth. In this study, we present the abundances and isotopic compositions of C, N and some noble gases in a Hayabusa 2 sample
A0219 (as collaborative research under the Phase2 Kochi curation activity) and three CI meteorites (Orgueil, Ivuna and Alais).
These measurements were performed using stepped combustion QEGA (Quantitative Evolved Gas Analysis) methods. It is
important to note that utmost care has been taken to avoid any exposure of Hayabusa 2 material to the terrestrial atmosphere,
from the time of the recovery of the sample capsule in Australia to sample allocation and preparation (in gloves box filled withpure N2) and loading (with portable gate valve) for analysis by the Finesse instrument [5, 6] at the Open University. The sample
aliquots used for the stepped combustion and QEGA were 2 and 0.5 mg respectively.
1. Hydrogen. Release of H2 from A0219 during EGA occurs over a broad temperature range (400-1000 oC) with the major
peak at 730 oC, similar to what is observed for the three CIs and seems to be associated with decomposition/oxidation of theorganic macromolecular material. The total concentration (0.3 wt.%) of the molecular hydrogen in A0219 is also similar to thatfound in other CIs.
2. Water. In contrast to all other CIs analysed, the release of H2O in A0219
61.2 10ohas a single peak with maximum at ~550 C: for Orgueil, Ivuna and Alais, theA0219
6Orgueil
1.0 10Ivuna
H2O release is bimodal with an additional (apart from that at 530-570 oC) peak
Alaisoo5
at low (~250 C) temperature (Fig.1). The peak at 530-570 C is thought to be
8.0 10associated with structural transformation of phyllosilicates at which their
56.0 10hydroxyl groups are released in the form of water. The low temperature peaks in
5CIs can be related to the adsorbed and/or hydroxide decomposition water release,
4.0 10associated with terrestrial weathering. In another study, the Hyabusa 2 sample
52.0 10analysed by TG-MS [7] showed a small peak of water at 100 oC, which was taken
0.0
as evidence of heating on the surface of the asteroid to be limited to below 1000 100 200 300 400 500 600 700 800 900 1000
ooC. However, the results here (Fig. 1) show no measurable water release below
Temperature, CFigure 1. Release pattern of H2O.
~300 oC; the quadrupole MS signal at these temperatures is at the backgroundlevel (<100) cps. As saponite can readily resorb water from atmosphere, it ispossible that the release at 100 oC reported by Yokoyama et al. [6] is terrestrial contamination, and that the samples have beenheated on the Ryugu’s surface to temperatures of up to 300 oC. The total water content determined in A0219 (7.6±1.5 wt. %) issimilar to that published for other Hayabusa 2 samples [6].
3. Carbon. Stepped combustion results clearly indicate that most of600
80
A0219
carbon in Hayabusa 2 (as in other CIs [8]) is associated with the50060
macromolecular organic material and carbonates (Fig. 2). CO2 from the latteris released at ~600 oC, characterised by a relatively high 13C values (up to4004080‰) and present in CIs in variable amounts. In that sense, A0219 is not300
different from other CIs, though its carbonate concentration is relatively high.
20
The petrographic studies of the Hayabusa 2 samples [6, 8] confirm the200
presence of Ca, Ma and Fe carbonates. Clearly, A0219 contains very little, if0100
any, presolar SiC, signature of which (~1200 ‰ in its pure form) is often seenin CIs as enhanced 13C (up to few hundred per mile) at 1100-1300o C. EGA
0-20
200 400 600 800 1000 1200 1400
data show that carbon is released as both CO2 at relatively low T and CO atoTemperture, Chigher T. Apart from decomposition of carbonates, these gases appear to beFigure 2. Release of C and 13C variationsa result of oxidation of organic material in chemical reaction of the latter withduring stepped combustion.
the oxygen-bearing minerals. The total range of the carbon release is similar
to that observed for molecular hydrogen confirming that all the species are associated with the macromolecular organics. The13

 C, ‰oNitrogen yeild , ng/ C

total concentration of carbon determined by stepped combustion and QEGA are 6.3 and 4.6 wt. %, respectively that are within
the range observed for CIs.
4. Nitrogen. During stepped combustion, nitrogen release is correlated with30100
that of carbon indicating that it is one of the major constituents (along with C andA0219H) of the macromolecular material. This is observed for the Hayabusa 2 and all CI
2580samples. The variations in 15N in the temperature steps are also similar to those20
seen in other CIs (Fig. 3). In particular a characteristic feature of the variations
6015(along with the presence of the relatively isotopically heavy organic component)
40
is the excursion of the 15N to the isotopically light values at ~400 oC that could
10
be explained by contribution from presolar nanodiamonds, pure separates of which
20
5have 15N ~-350 ‰. However, the calculated concentration of the nanodiamonds
00in the Hayabusa 2 sample using two-component mixing model with the200 400 600 800 1000 1200 1400
oTemperture, C
isotopically heavy N shown by the dashed line (Fig. 3) and 15N = -350 ‰Figure 3. Release of N and 15N variations
assuming 1 % of the N in the nanodiamonds is significantly higher (by a factor ofduring stepped combustion.
2-3) than in fact observed in the most primitive meteorites. The same is true for15

 N, ‰Orgueil and Tagish Lake [8]. Therefore, there must be another more significant
source of the isotopically light N component (possibly phase Q) with isotopic composition of N as light as the solar values (15N~-400 ‰), and which is oxidised in the same temperature range as nanodiamonds [5]. Nitrogen could not be identified by EGA
because of the dominant presence of CO at m/z=28.
5. Sulphur. Compared to all Cis, A0219 contains almost no sulphur. It is released at 300 oC and its estimated concentrationis ~1.2 ppm, while CIs contain a few wt. % of sulphur. It is a surprising result and the reason for such a low concentration is notcompletely clear but may reflect sample heterogeneity. Further analyses need to confirm it. Only a part of sulphur in CIs is
associated with terrestrial contamination. It follows from multicomponent sources of its release observed over a wide temperature
range including elemental, organic, sulphite and sulphide sulphur as well as from its isotopic composition [10]. Investigation ofother Hayabusa 2 samples by TG-MS [7] also indicated that the SO2 signal is very low though petrographic data showed thepresence of different sulphide minerals [7, 8]. On the other hand, in some works [11] it was suggested that most of sulphur inthe meteorites is due to terrestrial contamination. Therefore, the low S concentration in the Hayabusa 2 samples is arguably as aresult of the absence of any terrestrial contamination.
6. Noble gases. The 4He, 20Ne and 36Ar relative abundances in A0219 correspond to a mixture of solar and planetary (Q)components. The isotopic composition of Ne shows a very small contribution of the cosmogenic component: most of theexperimental points plots on the solar Ne fractionation line which is also a mixture of the solar and Q Ne, so that a contributionof the latter cannot be excluded. The data for other Hayabusa 2 grains [9] show Ne isotopic composition both without and withsome contribution of the cosmogenic component. The A0219 material and other Hayabusa 2 grains with very little cosmogenic
Ne contribution appear to have been exposed to solar wind radiation for a relatively short time being buried at a depth wheregalactic cosmic rays cannot penetrate for a longer time.
Conclusions. The EGA indicates that the A019 sample does not contain a low-temperature water release suggesting that its
presence in all other CIs is due to terrestrial contamination. The very low sulphur content in the sample may also be an indicationthat sulphur in other CIs is also mostly due to terrestrial contamination. The A0219 Hayabusa 2 sample shows many features inC, N and noble gases abundance and isotopic compositions similar to those observed in CI chondrites. Carbonates concentrationin A0219 is relatively high compared to other CIs. Hayabusa 2 definitely belong to the CI meteorite clan.
References[1] Ito M. at al., 2022. Nat Astron (2022). https://doi.org/10.1038/s41550-022-01745-5. [2] Liu, MC., et al., 2022. Nat
Astron (2022). https://doi.org/10.1038/s41550-022-01762-4. [3] Greenwood R. C. et al., 2022. Nat Astron. 2022 (Accepted).
[4] Nakamura T. et al., 2022. Science 10.1126/science.abn8671. [5] Verchovsky A. B., 2017. Geochemistry International 55:
957. [6] Verchovsky et al. 2020. Planetary and Space Science 181, 104830. [7] Yokoyama T. et al., 2022. Science 7850. [8]Grady M. M. et al., 2002. Meteoritics & Planetary Science 37: 713. [9] Nakamura E. et al., 2022. Proc. Jpn. Acad. Ser. B 98:
227. [10] Airieaus S. A. et al., 2005. Geochim. at Cosmochim. Acta 69: 4166. [11] Velbel M. A. and Palmer E. E., 2011. Claysand Clay Minerals 59: 416.