Mercury (Hg) in Ryugu particles and implications for the origin of volatile elements in early Earth

doi:10.21203/rs.3.rs-4002901/v1

Solar system abundances of the elements, which are determined by spectroscopic measurements of the solar photosphere and laboratory analyses of CI (Ivuna-type) carbonaceous chondrites, are a cornerstone to understand the origin and evolution of planets and other constituents, such as asteroids and comets. Mercury (Hg) is one of the elements whose solar system abundance is still poorly constrained due to no observable lines for Hg in the solar spectrum and large variations of the Hg abundance in CI chondrites caused by mainly terrestrial contamination. Here we determined elemental abundances including Hg for uncontaminated CI-like material from asteroid Ryugu by the Hayabusa2 spacecraft. The new solar system abundance of Hg is 0.907±0.108 atoms/10⁶ Si atoms. Our results demonstrate that Hg in bulk silicate Earth originated from the addition of chondritic material after core formation, late sulfide segregation and/or degassing, and volatile elements are depleted in late-accreted materials relative to CI chondrites.

Earth and environmental sciences/Planetary science/Geochemistry

Earth and environmental sciences/Solid Earth sciences/Geochemistry

Mercury (Hg) is geochemically classified as a chalcophile element and is the most volatile metal, with a 50% condensation temperature of 252 K at a total pressure of 10^− 4 bar for a solar composition gas^1,2. It has been demonstrated that Hg is the first metal element released from meteorites during heating and can be used as a tracer for their thermal history³. The highest volatility of Hg makes it a more powerful tracer for the thermal processes taking place in the early solar nebula and during planetary formation. In spite of this scientific importance, the accuracy of the published Hg values for meteorites is questionable, primarily due to terrestrial contamination⁴, analytical difficulties⁵ and/or the heterogeneous distribution of HgS in chondrites⁶. As a consequence, even for CI chondrites, which are the most chemically primitive meteorites and have the bulk chemistry (except for volatile elements) resemble that of the Solar System, the Hg abundance shows significant intra- and inter-sample variations from 0.18 to 500 µg g^{− 1 6}. The solar photosphere spectrum cannot be used to estimate the solar system Hg abundances due to the lack of observable lines¹. Theoretical calculations have yielded a 0.34 Hg atoms per 10⁶ Si atoms for the solar system⁷, but the accuracy of this value is called into question because of no reliable experimental data for comparisons. Thus, Hg is one of the elements whose abundance in the solar system still remains poorly known. In this paper, we report the new constraint on the solar system Hg abundance value based on the measurements of uncontaminated CI-like material from asteroid Ryugu returned by the Hayabusa2 spacecraft and examine the implications of this data for the origin of Earth’s volatile inventory.

The Hayabusa2 spacecraft collected surface and subsurface materials weighing approximately 5.4 g from the C-type asteroid Ryugu and successfully returned these materials to the Earth on December 6th, 2020. After the initial examinations of Ryugu particles at the JAXA curation facility^8,9, sub-samples of materials were distributed to initial analysis and curation teams for further detailed study^10–12. The results of these investigations have demonstrated that Ryugu has a composition and mineralogy closely similar to CI chondrites^10–13. Due to the careful handling of Ryugu samples since return, they provide a unique opportunity to determine accurately the chemical abundances of a range of elements that are more prone to terrestrial contamination.

Instrumental neutron activation analysis (INAA) is a powerful technique for quantifying the elemental composition to a high degree of accuracy and precision, with only minimal sample preparation. As a result, this significantly reduces the potential effects of terrestrial contamination derived from handling and processing of the samples on the data fidelity. These analytical advantages have resulted in INAA being frequently used for the analyses of extraterrestrial materials¹⁴. In this study, INAA was applied to the five Ryugu particles (C0068, A0002, A0029, A0037, and A0098) weighing about 8 mg in total to determine their elemental compositions, including Hg, whose abundance was not obtained in the earlier studies^11–13. In this study, to avoid the possibility of terrestrial contamination, sample preparation was undertaken in a glove box containing purified N₂ (Methods).

Concentrations of thirty-three elements determined by INAA from the five Ryugu particles are presented (Table 1) and are compared with our data on the CI chondrite Orgueil obtained in this study. The elemental abundance data presented here include Cl, Br, Ru, rare earth elements (REE), Ta and Hg, which are more comprehensive than the previous study¹⁰ and are consistent with the previously reported values obtained by mass spectrometry (Supplementary Fig. 1)^11–13. It can be seen that there are no systematic differences in chemical compositions between the samples from Chambers A and C. Ryugu particles show large variations in Ti, Ca, Mn, REE, Ta and Au. The large enrichment in Ta (7.88 µg g^− 1 or 430 × CI for A0098) compared to the chondritic value, which was also observed in the previous studies^11–12, and can be explained by the contamination with projectile materials made of Ta and Cu. Large variations in Ca and Mn, and REE seen in this study primarily reflect the heterogeneous distributions of carbonates and phosphates present in Ryugu particles (see the Supplementary Material).

Cr- and CI-normalized lithophile, and siderophile and chalcophile element abundances are plotted in Figs. 1 (a) and (b), respectively. For ultra-refractory to common lithophile, siderophile and chalcophile elements, Ryugu particles have a flat pattern and their relative abundances are indistinguishable from those of CI and CM chondrites. Moderately volatile elements in Ryugu particles are not depleted relative to CI chondrites, while depletions of the elements with factors of 0.5 to 0.6 can be seen in CM chondrites. These new results reinforce the conclusion that Ryugu particles are chemically more similar to CI chondrites and some CY chondrites (e.g., Y-82162) than CM chondrites and Tagish Lake (Supplementary Figs. 2).

Cr, CI-normalized abundances of elements scatter around unity with the notable exception of Hg (Fig. 1). The Hg values for the four Ryugu particles (C0068, A0002, A0029 and A0037) are consistently higher than the average value of CI chondrites¹⁵, with enrichment factors of 2.2 to 3.1 (Fig. 1). Particle A0098 does not contain enough Hg for concentration determination. Hg abundances in Ryugu particles are compared with literature values from CI and CM chondrites (Fig. 2), and these values fall within the range of CI and CM chondrites. Hg values for Ryugu particles are lower than those for almost all of CI chondrites which were not used to compile Hg values for CI values¹⁵.

The new Hg values measured from Ryugu particles could help define a more accurate solar system abundance than in previous studies^7,15. The mean Hg value for Ryugu particles is 0.806 ± 0.096 µg g^− 1, which is about three times higher than the compiled value for CI chondrite¹⁵. The mean Si value for Ryugu particles analyzed in this study was estimated to be 12.4 wt% using a value of 1.10 for the mean Si/Mg ratio^11,12, and the mean value for Mg of our Ryugu particles. Thus, the Hg abundance was calculated to be 0.907 ± 0.108 atoms/10⁶ Si atoms, which is about three times higher than the previous values based on theoretical calculation (0.34 ± 0.04)⁷ and from the analyses of CI chondrite (0.376 ± 0.156)¹⁵.

Our new Hg data provides the best estimate of the solar system abundance for this element. Because of its unique cosmochemical and geochemical behaviors, Hg can be used as a powerful tool for understanding the processes responsible for the depletions of siderophile and chalcophile elements in the terrestrial planets and for the source of their volatile elements.

Volatile elements are significantly depleted in bulk silicate Earth (BSE) as well as in chondrites and achondrites relative to CI chondrites¹⁶. Depletions of these elements are roughly correlated with volatility as expressed by their condensation temperature. This volatility trend is defined by a distinct correlation of abundances of moderately volatile lithophile elements such as Li, Na, K, and Rb, with condensation temperature (Fig. 3). As shown in Fig. 3, most siderophile, chalcophile and atmophile elements are depleted relative to lithophile elements of similar volatility, and these depletions are considered to be caused by core-mantle differentiation, a late Hadean sulfide matte and/or evaporation^17–19. The newly estimated Hg value of the solar system indicates that Hg in BSE is more depleted than previously estimated²⁰ and its degree of depletion relative to the volatility trend is a factor of 20 to 60, which is comparable to the corresponding depletion factors for S, Se and Te (Fig. 3).

Depletions of chalcophile and siderophile elements (P, S, Co, Ni, Zn, Ga, Ge, As, Se, Mo, Pd, Ag, In, Sb, Te, W, Pt, Au and Bi) in BSE have been explained by core formation and/or a late Hadean sulfide segregation^21–27. As Hg is classified as a chalcophile element², Hg could be extracted from the mantle to the core during accretion of the Earth. In considering a simple equilibrium scenario between metal and silicate liquid or between sulfide and silicate liquid, the partition coefficient of Hg is expected to be between 50 to 230, assuming complete retention of Hg during the magma ocean stage. However, no such partition coefficients have been experimentally determined. As isotope fractionation between metallic and silicate liquid has been reported for some elements with the silicate phase being enriched in the heavier isotopes^28–30, similar effects could be expected from the removal of Hg into core and/or sulfide-rich material. Isotopic fractionation of Hg between metallic and silicate liquid has never been experimentally evaluated, but it has been found that BSE is slightly isotopically heavier than the bulk enstatite chondrites^6,31,32, which are thought as building blocks for Earth³³. Therefore, the depleted Hg abundance and heavier Hg isotopic compositions in BSE could have been a result of core formation and/or a late Hadean sulfide matte.

An alternative mechanism that could cause the depletion of Hg in BSE is degassing during the Earth’s accretion. The depletions for moderately volatile elements such as S, Zn, Cu, Ga, In and Sn in BSE were explained by evaporation during Earth’s accretion^17,34. Hg is the first metal element that evaporates from meteorites during heating, and the most labile metal element in carbonaceous chondrites³. Thus, the observed depletion of Hg in BSE could be caused by the degassing during Erath’s accretion. This process could have also caused isotope fractionation, leaving BSE enriched in the heavier isotopes of Hg. An experimental study has demonstrated that δ²⁰²Hg in residues produced by kinetic evaporation reached about + 10‰ when 90% of Hg was evaporated³⁵. However, given that Hg isotopic compositions of BSE fall within the range defined by chondrites^6,31,32, a viable mechanism for Hg depletion in BSE cannot be explained by degassing only.

The two mechanisms discussed above indicate that the Hg depletion in BSE can be explained by indigenous processes. The so-called ‘late veneer’ model involves an exogenous origin for the BSE profile. Highly siderophile elements (HSE) abundances for mantle-derived samples are much higher than estimated from partition coefficients between metallic and silicate liquid, and their relative abundances are chondritic. These chemical features can be explained by a late addition of chondritic material after core formation^36–39. This concept was further expanded to be a potential source of volatiles such as water, nitrogen, carbon and the noble gases for Earth^24,40,41. Although the exact nature of the accreted materials remains controversial, they are most likely to be chondrites-like materials^40–43. The relative abundance of Hg in BSE is roughly plotted in the range estimated by 0.5 ± 0.2% of addition of chondritic material to BSE (Fig. 3), which was estimated from HSE abundances in BSE³⁸. If some significant amount of Hg was left in the mantle during Earth accretion, the Hg abundance in BSE should be higher than estimated by the trend of late accreted chondritic material. Thus, it is likely that Hg must have been efficiently extracted from the mantle before a late addition of chondritic material, and that the dominant source of Hg in BSE is the late accreted chondritic material, which can explain the consistency of Hg isotopic compositions between BSE and chondrites^6,31,32. The mechanism of depletion of Hg in BSE should be core-mantle differentiation, a late Hadean sulfide segregation and/or degassing. This mechanism for Hg depletion in BSE is consistent with the previous studies^27,44. A further implication is that a late addition of material would likely be depleted in volatile elements compared to CI chondrites. Due to the much lower relative abundance of Hg in BSE compared with those of HSE, S, Se and Te, the late accreted material must have been composed of CM chondrite-like material or a mixture of CI chondrite and other materials having the depleted volatile elements abundances^45,46. As each group of carbonaceous chondrites also has a wide range of Hg abundances, their relative abundances remain uncertain, and Hg abundances for carbonaceous chondrites least affected by contamination will be essential.

In this study, taking advantage of the fact that Ryugu particles are chemically similar to CI chondrites and the most uncontaminated asteroidal materials so far^10–13,47, we re-estimated the solar system abundance of Hg, which has been quite uncertain for a long time. The new Hg abundance in the solar system indicated that Hg in BSE is definitely depleted relative to the volatility trend and its degree is similar to those of S, Se, and Te. The elemental abundance and isotopic compositions of Hg in BSE could have been produced by core-mantle differentiation, a late Hadean sulfide matte and/or degassing, followed by late addition of chondritic material. It is likely that late added material is depleted in volatile elements. The Hg abundances are highly variable not only in CI chondrites, but also in other groups of carbonaceous chondrite meteorites. The samples of asteroid Bennu were returned to Earth by the OSIRIS-REx mission. These new samples will allow us to investigate the Hg abundances in another uncontaminated asteroidal material and expand our understanding of planetary accretion and differentiation of Earth based on these new data.

Data availability

Correspondence and requests for materials should be addressed to N.S. All analytical data related to this manuscript will be put on the JAXA Data Archives and Transmission System (DARTS) after a one-year proprietary period.

Acknowledgements

We thank all scientists and engineers of the Hayabusa2 project for their dedication and skills to bring these precious particles back to Earth from the asteroid Ryugu. We thank the National Institute of Polar Research, Tokyo for providing the sample of Orgueil. This research was performed by using facilities of the Institute for Integrated Radiation and Nuclear Science, Kyoto University. This research was supported in part by the JSPS KAKENHI (18H01312 and 19H01959 to N.S., JP18K18795 and JP18H04468 to M.I., 19H01959 to A.Y., 18H01312 and 19K21993 to S.S.)

Author contributions

N.S. led the project and wrote the initial draft. M.I., A.Y., N.T., M.U., N.I., M.K., R.C.G., M.-C.L., T. Ohigashi., K.U., A.N., K.Y., H.Y., Y.Kodama., K.H., I.S., I.O. and Y.Karouji. conducted sample handling and preparation processes of Ryugu grains. INAA was performed by N.S., and S.S.. A.N., K.Y., A.M., M.N., T.Y., T. Okada., M.A. and T.U lead the JAXA curation activities for initial characterization of allocated Ryugu particles. S.N., T. Okada., T.S., S.T., F.T., M.Y., S.W. and Y.T. administered the project and acted as principal investigators. All authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing interests.

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Samples and standards

Among the eight Ryugu particles from both Chambers A and C allocated to the Phase 2 Kochi team¹⁰, the five Ryugu particles (C0068, A0002, A0029, A0037, and A0098) were used for INAA. Samples of meteorites (Orgueil and Murchison) were used for comparison. Chips of Orgueil weighing 0.21 g were carefully ground in clean agate mortars at the National Institute of Polar Research, Japan. An aliquot of this powdered specimen was allocated to us. For the Murchison meteorite, an aliquot was taken from the same powdered specimen used in the previous study⁴⁸. Smithsonian Institution (SI) Allende meteorite sample (split 22; position 30) and BHVO-2 and BCR-2 (U.S. Geological Survey) were used for evaluation of the accuracy of our INAA data. JB-1 (Geological Survey of Japan) was used as the standard reference material.

Preparations of sample and standard samples

Two Ryugu particles (C0068 and A0098) were divided into several chips using a tantalum chisel. Each particle was picked up using tweezers and put into a high-purity polyethylene bag. The other three Ryugu particles (A0002, A0029, and A0037) were cut by a counter-balanced diamond wire saw (Meiwa Fosis Corporation DWS 3400). Similar to C0068 and A0098, catted pieces were put into a high-purity polyethylene bag. Samples were further doubly sealed in a high-purity polyethylene sheet. Sample preparations for Ryugu particles were performed in a glove box under a purified N₂ environment at SPring-8 to avoid terrestrial contamination from the surrounding environment. Ga, As, Se, Ru, Sb, Os, Ir, and Au were prepared by dropping a proper amount (10 to 50 μg) of concentration-known standard solutions (FUJIFILM Wako Pure Chemical or SPEX) of these elements on the two sheets of filter papers and used as reference standard samples. For Cl and Br, chemical reagents such as KCl (99.9% purity; FUJIFILM Wako Pure Chemical) and KBr (99.99% purity; Soekawa Chemical) were used as reference standard samples. For reference standard sample for Hg, JSAC 0601-2 and 0602-2 were used. To evaluate our Hg value, NIES CRM No. 13 Human Hair was also analyzed. Preparations of these geological (JB-1, BHVO-2, and BCR-2) and cosmochemical (Orgueil, Murchison, and Allende) samples, and reference standard samples were performed at Tokyo Metropolitan University.

INAA procedure

INAA was performed at the Institute for Integrated Radiation and Nuclear Science, Kyoto University. Samples were irradiated two times with different irradiation periods chosen according to the half-lives of the nuclides used for elemental quantification. First, samples were irradiated for 30 s in pneumatic irradiation tube no. 3 with thermal and fast neutron fluxes of 4.6 × 10¹² and 9.6 × 10¹¹ cm^-2s^-1, respectively, to determine Mg, Al, Cl, Ca, Ti, V, and Mn abundances. Chemical reagents such as MgO (99.99% purity; Soekawa Chemical), Al (99.9% purity; Soekawa Chemical), and Si metals (99.999% purity; FUJIFILM Wako Pure Chemical) were also irradiated to correct for interfering nuclear reactions such as (n,p). Sodium chloride (99.99% purity; MANAC) was also irradiated with the samples to correct for neutron flux variations. After neutron irradiation, the outer polyethylene sheet was replaced with a new sheet, and gamma rays emitted from the samples and reference standards were immediately measured using Ge detectors. After 24 hours, the same samples were re-irradiated for 4 hrs in pneumatic irradiation tube no. 2 with thermal and fast neutron fluxes of 5.6 × 10¹² and 1.2 × 10¹² cm^-2s^-1, respectively, to determine Na, K, Sc, Cr, Fe, Co, Ni, Zn, Ga, As, Se, Br, Ru, Sb, La, Sm, Eu, Yb, Lu, Ta, Os, Ir, Au, and Hg abundances. Gamma-ray counting was carried out five times with different cooling intervals over a period of 4 months at the Institute for Integrated Radiation and Nuclear Science, Kyoto University and RI Research Center, Tokyo Metropolitan University. The analytical procedure by INAA was the same as those described in the previous study⁴⁸. For the determination of Hg abundance, Orgueil along with two reference standards (JSAC 0601-2 and 0602-2) and a filter paper dropping of Se standard were irradiated for 60 min in pneumatic irradiation tube no. 2. Gamma-ray counting was carried out several times with different cooling intervals over a period of 3 months at RI Research Center, Tokyo Metropolitan University.

Data reduction of INAA

For quantification, a relative method using JB-1 as the reference materials was applied for the determination of Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Zn, Rb, Sr, Cs, Ba, La, Ce, Sm, Eu, Tb, Yb, Lu, Hf, Ta, Th and U. Values for JB-1 used as the reference materials were taken from Jochum et al.⁴⁹. For other elements (Cl, Ga, As, Se, Br, Ru, Sb, Os, Ir, and Au), filter papers dropping of these elements or chemical reagents were used. When Ryugu particles were analyzed, the gamma-ray peak emitted from ²⁰³Hg in both Ryugu particles and Orgueil was detected. However, the reference Hg standard sample was not analyzed. Thus, Orgueil was used as a reference standard sample for the determinations of Hg abundances in Ryugu particles. Mercury abundance in Orgueil was determined using both JSAC 0601-2 and 0602-2. The obtained Hg value for Orgueil was used for the quantification of Hg abundances for Ryugu particles. The gamma-rays energies used for quantification are listed in Tables S1–S3.

In INAA, there are several potentially interfering nuclides and reactions. A check on interferences was performed by irradiation of chemical standards. Al and Mg abundances were determined from the radioactivities of ²⁸Al and ²⁷Mg, which were also produced from ²⁸Si(n,p)²⁸Al and ²⁷Al(n,p)²⁷Mg reactions. These interfering nuclides were monitored by analyzing chemical reagents of Si, Al, and MgO. The 264.7 keV peak emitted by ⁷⁵Se was used for the quantification of Se abundances. However, ¹⁸²Ta also emitted gamma-ray at 264.1 keV. In the case of meteorite samples, the 1189.0 keV peak of ¹⁸²Ta could not be detected, which was used for the quantification of Ta. Thus, the spectral interference from ¹⁸²Ta was negligible for determining Se using 264.7 keV peak in the analysis of chondrites. As Ta could be detected in A0098 due to the contamination with projectile materials during sample collections, interference correction of ¹⁸²Ta was necessary. As the spectral region around 264 keV in geological samples such as JB-1, BHVO-2, and BCR-2 mostly came from gamma-ray emitted from ¹⁸²Ta due to their lower Se abundances, JB-1 was used for correction. The ratio of the intensity of the gamma-ray peak of 1189.0 keV to that of the 264.1 keV peak was estimated using JB-1. This ratio was applied to the 1189.0 keV peak of A0098, and the intensity of the gamma-ray peak of 264.1 keV of ¹⁸²Ta was subtracted from the those of 264.7 keV peak of Se. The 279.2 keV peak emitted by ²⁰³Hg was used for the quantification of Hg abundance. However, the radionuclides such ⁷⁵Se and ¹⁸²Ta also emitted gamma-ray at 279.5 keV. To obtain an accurate Hg value, spectral interferences from ⁷⁵Se and ¹⁸²Ta should be corrected. The ratios of the intensity of the gamma-ray peak of 264.7 keV to the 279.5 keV and 1189.0 keV to the 279.5 keV were estimated using a Se standard and JB-1, respectively. These ratios were applied to the 264.7 and 1189.0 keV peaks of the sample, and intensities of the gamma-ray peak of 279.5 keV of ⁷⁵Se and ¹⁸²Ta were subtracted from those of 279.2 keV peak of ²⁰³Hg. As no ¹⁸²Ta was detected for the four Ryugu particles (C0068, A0002, A0029, and A0037) and Orgueil, spectral interference correction of ¹⁸²Ta was not performed.

Table 1. INAA data for the five Ryugu particles and Orgueil^a.

Element	unit	C0068^b (0.530 mg)			A0098^b (1.624 mg)			A0029 (1.627 mg)			A0037 (0.698 mg)			A0002 (3.551 mg)			Orgueil
Element	unit	C0068^b (0.530 mg)			A0098^b (1.624 mg)			A0029 (1.627 mg)			A0037 (0.698 mg)			A0002 (3.551 mg)			Orgueil
Na	[%]	0.530	±	0.002	0.604	±	0.001	0.603	±	0.001	0.606	±	0.001	0.595	±	0.001	0.301	±	0.001
Mg	[%]	11.4	±	0.5	11.7	±	0.7	11.7	±	0.4	12.3	±	0.5	9.50	±	0.31	9.71	±	0.36
Al	[%]	1.05	±	0.04	1.08	±	0.03	1.01	±	0.03	0.989	±	0.051	0.928	±	0.026	0.911	±	0.046
Cl	[µg g^-1]	901	±	114	1020	±	80	904	±	98	886	±	134	1180	±	60	285	±	66
K	[%]	0.0637	±	0.0102	0.0535	±	0.0035	0.0552	±	0.0031	0.0567	±	0.0065	0.0694	±	0.0044	0.0559	±	0.0048
Ca	[%]	0.409	±	0.034	0.625	±	0.195	3.01	±	0.48	4.34	±	0.79	0.436	±	0.122	0.973	±	0.182
Sc	[µg g^-1]	7.23	±	0.04	6.99	±	0.03	7.42	±	0.02	7.75	±	0.02	5.42	±	0.01	6.33	±	0.01
Ti	[%]				0.0853	±	0.0298	0.166	±	0.054							0.106	±	0.039
V	[µg g^-1]	80.2	±	5.8	59.1	±	3.9	55.5	±	4.2	53.3	±	6.5	55.0	±	3.0	50.3	±	3.8
Cr	[µg g^-1]	3,250	±	30	3,230	±	30	2,740	±	30	2,970	±	20	2,800	±	20	2,790	±	30
Mn	[%]	0.0926	±	0.0035	0.198	±	0.005	0.615	±	0.014	0.712	±	0.017	0.105	±	0.003	0.206	±	0.005
Fe	[%]	22.2	±	0.3	22.4	±	0.1	21.6	±	0.1	21.8	±	0.1	20.2	±	0.1	19.3	±	0.1
Co	[µg g^-1]	667	±	4	636	±	3	524	±	2	563	±	3	492	±	2	543	±	2
Ni	[µg g^-1]	13,500	±	100	12,800	±	100	10,500	±	100	11,700	±	100	11,600	±	100	10,600	±	100
Zn	[µg g^-1]	419	±	17	410	±	29	325	±	14	325	±	11	305	±	10	279	±	9
Ga	[µg g^-1]	15.3	±	2.6	11.7	±	0.3	11.1	±	0.9	10.5	±	1.8	13.1	±	0.9	11.6	±	1.3
As	[µg g^-1]	2.56	±	0.19	2.06	±	0.09	1.76	±	0.09	2.15	±	0.16	1.90	±	0.09	1.80	±	0.13
Se	[µg g^-1]	26.5	±	0.5	25.9	±	0.6	22.1	±	0.5	23.8	±	0.7	22.1	±	0.4	20.0	±	0.3
Br	[µg g^-1]	4.12	±	0.30	3.39	±	0.15	3.09	±	0.17	4.36	±	0.20	4.03	±	0.12	32.8	±	0.5
Ru	[µg g^-1]							0.650	±	0.231	0.797	±	0.167	1.07	±	0.25	0.339	±	0.171
Sb	[µg g^-1]	0.160	±	0.023	0.236	±	0.026	0.208	±	0.022	0.259	±	0.042	0.156	±	0.024	0.169	±	0.023
La	[µg g^-1]	0.182	±	0.033	0.539	±	0.041	0.406	±	0.037	0.410	±	0.054	0.0722	±	0.0190	0.229	±	0.039
Sm	[µg g^-1]	0.120	±	0.004	0.303	±	0.007	0.296	±	0.005	0.303	±	0.011	0.0409	±	0.0021	0.150	±	0.004
Eu	[µg g^-1]	0.140	±	0.027	0.147	±	0.020	0.151	±	0.024	0.311	±	0.033	0.0568	±	0.0077	0.0799	±	0.0095
Yb	[µg g^-1]				0.373	±	0.051	0.271	±	0.035	0.480	±	0.100	0.0915	±	0.0217	0.200	±	0.041
Lu	[µg g^-1]	0.0181	±	0.0040	0.128	±	0.011	0.0348	±	0.0065				0.0267	±	0.0064	0.0344	±	0.0064
Ta	[µg g^-1]				7.88	±	0.33
Os	[µg g^-1]	0.565	±	0.108	0.497	±	0.104	0.476	±	0.071	0.548	±	0.046	0.519	±	0.090	0.593	±	0.100
Ir	[µg g^-1]	0.620	±	0.006	0.678	±	0.009	0.636	±	0.007	0.557	±	0.006	0.533	±	0.005	0.514	±	0.005
Au	[µg g^-1]	0.0737	±	0.0016	0.193	±	0.002	0.115	±	0.002	0.142	±	0.003	0.241	±	0.002	0.153	±	0.002
Hg	[µg g^-1]	0.793	±	0.210	<1.3			0.944	±	0.299	0.762	±	0.189	0.726	±	0.175	196	±	5

^aUncertainties cited only include the counting statistics (1s) in gamma-ray counting.

^b Except for Cl, Br, REEs, Ta, Hg, other elements abundances were reported by Ito et al.¹⁰.

There is NO Competing Interest.

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Supplementary Table S1, Supplementary Table S2, Supplementary Table S3
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Supplementary Information

Mercury (Hg) in Ryugu particles and implications for the origin of volatile elements in early Earth

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