Characterization Of Early Solar System Aqueous Fluids In Ryugu Samples
Michael Zolensky1, Robert Bodnar2, Andrei Dolocan3, JangMi Han4, Romy Hanna3, Iona Gearba3, Queenie Chan5,Trevor Ireland6, Megumi Matsumoto7, Akira Tsuchiyama8.
1NASA JSC, Houston, TX 77058, USA (michael.e.zolensky@nasa.gov); 2Virginia Tech, Blacksburg VA 24060,
USA;3Univ. of Texas, Austin TX 78712, USA; 4University of Houston, Houston TX 77204, USA; 5Royal Holloway
University, Egham Hill, Egham TW20 0EX, UK; 6University of Queensland, St Lucia 4072, Queensland, Australia;
7Tohoku University, Aoba-ku, Sendai, Miyagi, Japan; 8Ritsumeikan Univ., Kusatsu, Shiga, 525-8577, Japan
Introduction: The most direct and convincing evidence for the presence of water and organic molecules on
protoplanetary bodies is provided by fluid inclusions trapped in secondary minerals. Our previous research has
demonstrated that early solar system fluids have survived as fluid inclusions in a few astromaterials that escaped
significant shock, terrestrial alteration, and invasive sample handling [1-3]. We hypothesize that the bulk molecularand isotopic composition of individual fluid inclusions can be measured to provide ground truth for exploring andthermochemical modeling of the compositional and isotopic evolution of fluids in protoplanetary bodies including
asteroids, comets and icy moons.
This presentation is an update on our efforts to make measurements of elemental, molecular and isotopic
compositions of individual aqueous fluid inclusions in Ryugu samples.
Facilities: For the following XRCT and TOF-SIMS analysis, samples were prepared using the FEI Quanta 3D 600
Dual-beam Focused Ion Beam in the ARES -NASA-JSC Electron Beam Instrument Facility. For the X-ray Computed
Tomography (XRCT) scans we used the Zeiss 620 XRM instrument at the University of Texas High-Resolution Xray Computed Tomography Facility. For the Time of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS)
measurements we used the University of Texas Materials Institute’s TOF-SIMS 5 and TOF-SIMS 6 instruments (IONTOF GmbH) equipped with a pulsed Bi+ analysis ion beam (30 keV ion energy) and a O2+ sputtering ion beam (1 kVion energy). The TOF-SIMS instruments are capable of cooling the samples to -160 and -180C, respectively, andwithout this capability our measurements would be impossible.
Aqueous Fluids: Studies of aqueous alteration in primitive meteorites, based solely on secondary mineralassociations, have hinted that this process did not occur under a single set of conditions [4]. The temperatures ofalteration that have been suggested are highly variable, from below 0 to ~250°C. The fluid compositions must have
likewise varied, though this critical aspect is very poorly understood. Our previous molecular, O and H isotopic
measurements of fluids in halite in the Monahans and Zag meteorites [2,5] have shown considerable variation in fluid
composition even within individual crystals. For example, we suspect that early solar system aqueous fluids could
alternate between being S-rich and S-poor, based on the alternating pyrrhotite-magnetite alteration assemblage
observed in the Tagish Lake and Sutter’s Mill chondrites [6]. We know from our previous studies of aqueous fluidinclusions in extraterrestrial halite and calcite in the Sutter’s Mill C2 chondrite that the mineralizing fluids also
contained a significant concentration of mineralizing cations such as Fe, Mg, Ca, and volatiles such as CO 2 and Sbearing compounds in variable abundances (though the abundances are not yet determined) [2,7]. We observed CN-,a molecular fragment of a larger nitrogenous compound, in the aqueous fluid inclusions in a Ryugu pyrrhotite crystal[1-3]. Nakamura et al. [3] reported that the earliest formed phyllosilicates in Ryugu were rich in Na, indicating
significant compositional changes in the mineralizing fluid.
Ryugu Fluid Inclusion Measurements: Our recent successful, coordinated, XRCT and TOF-SIMS analyses ofindividual fluid inclusions in a Ryugu pyrrhotite crystal demonstrated that they consist of water, CO2, sulfur species,
and organic material, with H-, C-, O-, S- and OH- as the main fragments detected at these locations [1,3]. In addition,
various amounts of F-, Cl- and Ni- were found, together with Na+, Mg+, Al+, Cr+, K+ and Ca+. Larger organic fragments
such as C2-, C2H-, C3-, CO- and CN- were also detected, indicating the presence in these inclusions of more complex
organic molecules containing H, C, N and O. We can expect to see these and additional molecular fragments in other
Ryugu fluid inclusions. TOF-SIMS breaks apart molecules - it does not make new ones. Therefore, all these identified
species are fragments of once larger molecules which we can identify to some degree.
Measurement of the stable isotopic compositions of aqueous fluid inclusions in Ryugu samples will enable acomparison with our measurements of a few fluid inclusions in carbonaceous chondrites (e.g. [7]), and fluids
calculated to have reacted with other primitive samples (CI chondrites, OCs, HEDs, ureilites) which have δD ranging
from ~0-3000‰. Actual direct measurements of preserved trapped fluids would thus inform us about fluid changes
during aqueous alteration in a large suite of primitive bodies. Russell et al. [8] has suggested that CI materials form

two groups with distinct water/rock ratios, temperature ranges, and hydrogen isotope compositions. Are these truly
distinct groups or do these just represent endmembers of a poorly sampled complete range (as also suggested byRussell et al., [8])? Our planned analyses of individual fluid inclusion oxygen and hydrogen isotope compositions in
Ryugu samples will settle this issue as we will either observe narrow compositions or a compositional continuum.
Polished Ryugu sample C00025 contains large sulfides, magnesite, magnetite and dolomite crystals (Fig 1). We
have already FIBed several foils from this sample and subjected one of the FIB foils to TOF-SIMS measurements.
We detected no filled fluid inclusions, however we were limited to analyzing inclusions larger than about 3 μm using
the M5 TOF-SIMS instrument, and it appears the inclusions were far smaller (Fig.1). We plan to repeat themeasurements of this sample using the newly-installed M6 TOF-SIMS, which has greatly expanded capabilities. We
made XRCT scans of two additional Ryugu grains (A0175 and C0043) (Fig 2). From these preliminary measurements
we know that A0175 contains numerous pyrrhotite, carbonate, and, probably, apatite crystals with fluid inclusion
candidates measuring at least 3-5 µm in diameter, which will permit our planned TOF-SIMS measurements.
The TOF-SIMS analytical data are counts under the peaks for each species. An example of the data is shown in
Figure 3, which shows counts for OH- (indicative of H2O) and C- (here indicative of CO2). This sample was a synthetic
fluid inclusion standard (quartz) prepared by Bob Bodnar where the inclusions contained a 1:1 mixture of H 2O andCO2. As you can see from the included table, despite the fact that the sensitivity of the technique for CO 2 was much
lower than for H2O, 4/5 of the inclusions showed consistent counts for these species, meaning that with continued
calibration we can produce quantitative composition measurements for some species. We note that the signals for CO2
we observed in the Ryugu pyrrhotite crystal were more pronounced than those we obtained using the 50:50 standard,suggesting a very high abundance of CO2 in the Ryugu mineralizing fluid. In fact, solid CO2 sublimed rapidly in avacuum at our measurement temperature, making quantification very difficult.
In the coming year we will begin isotopic measurements of standards in synthetic fluid inclusions and Ryugu
pyrrhotites and carbonates we have already identified, as well as increasing our stock of pre-analyzed Ryugu crystals.
Fig. 1. Magnesite in Ryugu sample C00025 (left) BSE image ofMagnesite showing FIB pits. (right) SEI image FIB A foil
showing submicron-sized fluid inclusion candidates circled.
Acknowledgements: We thank JAXA for Ryugu samples, andthe NASA Hayabusa2 Participating Scientist Program.
References: [1] Zolensky et al. (2022) 85th Meeting of The
Meteoritical Society. Abstract 6011; [2] Bodnar et al. (2019) 50thLPSC Abstracts; [3] Nakamura et al. (2022) Science 377,10.1126/science.abn8671; [4] Brearley (2005) In Meteorites andthe Early Solar System II. D. S. Lauretta and H. Y. McSween Jr.,
Eds.; [5] Yurimoto et al. (2014) Geochemical Journal 48, 1-12;[6] Zolensky et al. (2014) MAPS 49, 1997-2016; [7] Tsuchiyama
et al. (2021) Science Advances 7, eabg9707; [8] Russell et al.
(2022) MAPS 57, 277–301.
(Left) Fig. 2. XRCT “slices” ofRyugu sample A0175. Fluid
inclusion candidates are arrowed.
(a-e) Pyrrhotite crystals. (f-g)
Probable carbonates. (h) Possible
apatite crystal.
(Right) Fig. 3. Results of TOFSIMS measurements of synthetic
fluid inclusion standard (quartz),with inclusions that contain a 1:1
mixture of H2O and CO2. Inclusions are numbered to match thetable (e.g. ROl1=1). Counts = cts.