A new primordial noble gas component in the solar system discovered in Ryugu asteroid

doi:10.21203/rs.3.rs-3443727/v1

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A new primordial noble gas component in the solar system discovered in Ryugu asteroid

https://doi.org/10.21203/rs.3.rs-3443727/v1

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published 14 Sep, 2024

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Ryugu is the C-type asteroid from which material was brought to Earth by the Hayabusa2 mission. A number of individual grains and fine-grained samples analysed so far for noble gases have indicated that solar wind and planetary (P1=Q) noble gases are present in Ryugu samples with concentrations higher than those observed in CIs, suggesting the former to be more primitive compared to the latter. We analysed three fine-grained samples from Ryugu, one of which contained a Xe concentration an order of magnitude higher (4x10^-7cc STP/g) than previously found in samples from Ryugu. Isotopically, this Xe resembles Q, but with a much stronger (by a factor of four) isotopic fractionation relative to solar wind and an ³⁶Ar/¹³²Xe ratio at least an order of magnitude lower than in P1. This new planetary primordial noble gas component (here termed P7) provides clues to constrain how the solar composition was fractionated to form the planetary components.

Physical sciences/Astronomy and planetary science/Planetary science/Early solar system

Physical sciences/Astronomy and planetary science/Planetary science/Asteroids, comets and Kuiper belt

“Solar” and “Planetary” are two of the most abundant primordial noble gas components found in solar system materials. The majority of the former is located in the Sun. Solar wind (SW) composition is commonly used as a proxy for the solar component since this is the only physical solar material available for laboratory analysis. Such analyses have been performed on species implanted into the surfaces of airless bodies such as asteroids (via meteorites) or the Moon, as well as into artificial targets exposed to the solar wind in space (Genesis mission¹), or on the surface of the Moon (Solar Wind Composition experiment²). SW isotopic and elemental compositions are expected to have been mass fractionated with respect to true solar composition during the SW formation process. However, the degree of the fractionation remains largely uncertain.

The planetary component (P1) is widespread in solar system materials and is present in many types of meteorites, including carbonaceous and ordinary chondrites³. It is located in a carbonaceous carrier phase (Q), the nature of which is as yet unidentified, but is known to be very rare and soluble in oxidising acids. The noble gas concentrations in the Q phase are apparently extremely high^3–4. Isotopic and elemental compositions of noble gases in this component are different from those in SW. The Q component shows some variations in Ne and Xe isotopic compositions in meteorites of different classes and metamorphic grades⁴. The elemental composition of the noble gas component indicates the presence of subcomponents with high ³⁶Ar^5–7, held in a water-soluble carrier phase. The isotopic composition of Kr and Xe in P1 can be produced from SW by mass fractionation (~ 10‰ AMU^− 1), though the mass fractionation line does not fit the compositions perfectly. Aside from mass fractionation, the addition of small amounts (1–2%) of r- and s-process isotopes is required to explain the difference between P1 and SW^8–11. Also, P1 has a significant excess of ¹²⁹Xe⁸ (when compared with the mass fractionation line), which formed as a result of the decay of extinct ¹²⁹I (T_1/2=17.6x10⁶ years).

Ryugu is the first C-type asteroid from which material has become available for laboratory study due to the successful Hayabusa2 mission, which collected and returned to Earth a relatively large (compared to the original Hayabusa mission) amount of the asteroid surface matter^12–14. According to remote spectroscopic data¹⁵, C-type asteroids are built from material very similar or identical to that of carbonaceous chondrite meteorites of the most primitive CI class. Indeed, a number of petrological, mineralogical, geochemical and isotope studies carried out so far^16–22 on the Hayabusa2 samples clearly identify Ryugu as a member of the Ivuna-type (CI) carbonaceous chondrite group, although there are some differences between Ryugu and CI meteorites. One example is in concentrations of the primordial planetary (P1) noble gases^23–24, which are generally higher in the Ryugu material than in meteorites. In addition, the Ryugu material is chemically closer to the solar composition than even Orgueil, and in this sense appears to be more primitive¹⁸, although it has undergone low-temperature (below 400 K²⁵) aqueous alteration^{19, 25}.

In the present study we analysed three fine-grained Ryugu samples (A0219, C0208 and C0209) by high-temperature resolution, stepped combustion using our mass spectrometric complex (Finesse instrumentation). He, Ne, Ar, C and N abundances and isotopic compositions were measured in all the samples, while Xe was measured in only two of them. Critically, the samples entirely avoided exposure to the terrestrial atmosphere prior to analysis. For details see the “Methods” section.

Noble gas concentrations and relative abundance

Data for bulk noble gases, nitrogen and carbon concentrations and Ne, N and C isotopic compositions in the Ryugu samples and in three CI meteorites, some of which were analysed in the present study, are shown in Table 1. For comparison, the ranges of noble gases, nitrogen and carbon concentrations and Ne, C and N isotopic compositions analysed in Ryugu samples in other studies^23–26 are also shown.

Table 1

Bulk noble gases, carbon and nitrogen in the Ryugu and CI samples
Sample	C wt. %	d¹³C, ‰	N, ppm	d¹⁵N, ‰	⁴He, cc STP/g	²⁰Ne, cc STP/g	²⁰Ne ²²Ne	²¹Ne ²²Ne	³⁶Ar, cc STP/g	¹³²Xe, cc STP/g	¹³²Xe ³⁶Ar
C0208	2.89	0.02 ± 0.81	923	36.5 ± 0.3	1.60e-3	2.24e-5	13.30 ± 0.30	0.0335 ± 0.0026	3.59e-6	1.78e-8	0.005
C0209	3.80	-1.70 ± 1.0	1491	29.4 ± 0.2	8.29e-4	3.09e-5	12.64 ± 0.54	0.0386 ± 0.0031	2.44e-6	4.00e-7	0.16
A0219	6.31	11.0 ± 1.0	2195	42.0 ± 0.5	4.25e-4	1.57e-5	13.30 ± 0.60	0.0347 ± 0.0072	3.56e-6	n.a.	n.a.
Orgueil	4.36	-15.2	2000	32.2	2.21e-4	n.a.	n.a.	n.a.	2.65e-6	1.64e-8	0.006
Tagish Lake²⁶	5.81	24.4	1217	67.5	3.22e-5	n.a.	n.a.	n.a.	1.33e-6	n.a.	n.a.
Ivuna	3.60	-14.4	2717	44.0	7.72e-5	6.75e-07	n.a.	n.a.	1.67e-6	1.68e-8	0.01
Okazaki et al., 2022²³	6.4–6.8	n.a.	700–900	1.7–43	6.35e-5- 5.71e-3	5.26e-8- 1.24e-5	6.43–12.87	0.0312–0.214	1.14e-6-1.42e-5	3.7e-9-3.54e-8	0.002–0.018
Naraoka et al., 2023²⁵	3.6-4	-4–1	1400–1700	40–60	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.

As can be seen from Table 1, ⁴He, ²⁰Ne, ³⁶Ar and ¹³²Xe concentrations in the Ryugu samples analysed in the present study and by Okazaki et al.²³, analysed in different laboratories all over the world, are in the same range except for ¹³²Xe in the sample C0209 which is an order of magnitude higher than the highest ¹³²Xe concentration found in other Ryugu samples^23,24. C and N concentrations and N and Ne isotopic compositions are also similar in all the samples shown in Table 1. The variations in d¹³C for the samples can be explained by different content of carbonates with isotopically heavy carbon²⁵.

Although concentrations of noble gases in the Hayabusa2 samples are generally higher than in carbonaceous chondrites, the Xe anomaly in C0209 is extraordinary and so it is necessary to exclude the possibility of any artefacts before it is accepted as real. One possible reason for this observation is contamination from the Xe ion engine used to navigate the Hayabusa2 spacecraft. However, according to the detailed time-sequence of the ion engine activity during flight to Ryugu the last time it operated was about half a year before Hayabusa2 arrived at the asteroid²⁷. Even in the very unlikely case of contamination from the engine after that, the Xe isotopic composition must be atmospheric or related to it. As can be seen in the next section, Xe in C0209 is not atmospheric and cannot be produced from atmospheric Xe by mass fractionation either. For the same reason, a leak in the vacuum system of the Finesse instrument during only the Xe analysis can also be excluded. In addition, a very specific release pattern of Xe from C0209 (see below) is also incompatible with such a possibility.

Thus, the extremely high Xe concentration in the sample C0209 must be accepted as real and if so, the very low ³⁶Ar/¹³²Xe ratio is also real. The relative abundances of measured light noble gases are in between SW and P1 compositions for all the samples including C0209. The same is true for the Ne isotopic composition in the analysed samples (Table 1). For the heavy noble gases, Ar and Xe, the experimental point for C0208 is also in the SW-P1 range, while the sample C0209 is outside of it (Fig. 1).

Isotopic composition of Xe in C0209

Experimental details for Xe isotope analysis can be found in the “Methods” section.

On three-isotope diagrams (except for ¹³⁴Xe/¹³²Xe vs. ¹³⁶Xe/¹³²Xe) the data points for combustion steps of the sample C0209 are almost all within the triangle with Xe-P1, Xe-HL (a component of presolar nanodiamonds³) and Xe with unknown composition, which we tentatively named Xe-X, as end members (Fig. 2). The same remains true if instead of Xe-P1 SW Xe is taken as one of the end-member components. As the Ryugu asteroid represents material similar to CI-type carbonaceous chondrites, it must contain Xe-P1 that is confirmed by laboratory studies^23–24of the Ryugu samples. On the other hand, the Ryugu surface regolith material collected by the Hayabusa2 mission was definitely exposed to SW radiation and, therefore, must contain a SW component. This is also confirmed by analyses of the Ryugu samples^23–24, however in most samples Xe-P1 dominates over SW. Thus, both SW Xe and Xe-P1 can contribute to the Xe isotopic composition of the C0209 sample. The data points corresponding to the main Xe release form a cluster on the opposite to the P1 or SW Xe end of the mixing lines. At higher temperature the data points move towards Xe-P1 (SW Xe) as well as to Xe-HL³ composition. The presence of the latter is confirmed by other analyses of the Ryugu samples^23–24 and is due to its release from presolar nanodiamonds, a common component of carbonaceous chondrites²⁸.

As can be seen on the ¹²⁹Xe/¹³²Xe vs. ¹³⁶Xe/¹³²Xe plot (Fig. 2), a contribution from ²⁴⁴Pu fission Xe cannot explain the experimental data. The same is also true for ²³⁸U fission Xe, which has ¹³⁶Xe/¹³²Xe ratio even higher than that for ²⁴⁴Pu. Contributions from these sources can also be excluded on the basis of low (0.009 ppm⁵) U (and consequently Pu) content in the Ryugu and extremely high Xe concentration in the sample.

Thus, Xe with an unknown isotopic composition (Xe-X) is required to explain the observations. As demonstrated by the three-isotope diagrams, Xe-X is not related to the terrestrial atmospheric composition. The pure composition of this Xe-X can be located on an extension of the mixing lines from P1 (or SW), but where exactly is not known. However, considering Xe isotope variations in combustion steps alongside cumulative Xe yield (Fig. 3), within nearly the entire Xe release the Xe isotope ratios remain almost constant despite Xe abundance in the steps varying by factors of 2–5. At higher temperatures, after more than 85–95% of Xe is released, the isotope ratios shift to Xe-P1, SW Xe, and Xe-HL compositions the same way as observed in Fig. 2. In other words, the contribution of Xe-P1 and/or SW Xe to the Xe budget at the temperature steps where Xe isotope ratios remain constant appears to be insignificant, or even absent. Thus, Xe in these low temperature (100-400^oC) steps can be considered as a pure Xe-X component. This interpretation agrees with the very high Xe concentration in the sample. Xe-P1 is released at a somewhat higher temperature than Xe-X (see below), which is why its signature is seen only after most of the Xe-X is gone. An alternative explanation for the constant Xe isotope ratio in the main Xe release would be that both components (even trapped in comparable amounts) have almost identical release patterns, which seems an unlikely scenario. We calculated the Xe-X isotopic composition as an average for the steps with constant isotope ratios and uncertainties as standard errors of the means (Fig. 3).

Thus, Xe-X is a new separate primordial Xe component.

Comparison of Xe-X with other primordial components

From the isotope ratios of Xe-X shown in Fig. 3 we calculated isotope ratios normalised to ¹³⁰Xe and plotted them in comparison with SW Xe (Fig. 4a).

It is clear that Xe-X can be largely explained by the mass-dependent isotope fractionation of SW Xe. However, the mass-fractionation line does not fit Xe-X perfectly: a significant deviation is observed for ¹²⁹Xe and minor (but outside the error bars) for ¹³¹Xe, ¹³²Хе, ¹³⁴Xe and ¹³⁶Xe. In this sense Xe-X is surprisingly similar to Xe-P1, including similar deviations of ¹²⁹Xe and small deviations at other masses from the corresponding mass fractionation lines (Fig. 4b), though the deviations have a different isotope structure for each component and are slightly higher for Xe-X than for Xe-P1. The only significant difference between the components is in the degree of mass fractionation from SW composition: Xe-X is much more strongly fractionated, by a factor of 3.5, than Xe-P1 (Fig. 4).

Origin of Xe-X

This observation suggests that Xe-X and Xe-P1 can be considered as two types of planetary components formed from the same solar composition likely through similar physical processes of mass fractionation, which occurred with different intensity in each case. In other words, Xe-X belongs to the same family of planetary components and can therefore be named Xe-P7 (next available number) according to the P nomenclature²⁸. The carrier of Xe-P7 is combustible in a similar manner to the carrier of Xe-P1: both are oxidized in nearly the same relatively low temperature (100-500^oC) ranges, which are only slightly different from each other (Fig. 5). This means that both appear to be carbonaceous and may be chemically similar. One of the explanations for the very high Xe-P7 concentration in C0209 may be due to its carrier’s ability to trap Xe much more efficiently than that of P1 and/or because of the relatively high concentration of P7 carrier itself in the sample.

As discussed above, most Xe released from C0209 belongs to P7 component; the signature of Xe-P1 appears above 400^oC where most of Xe-P7 is gone (Fig. 3, 4). Since the bulk concentrations and relative abundance of He, Ne and Ar in C0209 are similar to that in C0208, it is reasonable to suggest that these gases in C0209 mostly belong to P1 with some contribution of SW. However, from general considerations, it is impossible to imagine that P7 consists of only Xe without lighter noble gases. It is difficult to estimate how much He, Ne and Ar P7 is present in C0209 but it is clear that the measured ³⁶Ar/¹³⁰Xe in the sample represents an upper limit for pure P7.

Obviously the P7 component is not as widespread as P1: it has never been identified in any carbonaceous or ordinary chondrites and is present here only in one out of about 20 Ryugu samples analysed for Xe so far. The reason for that could be its low temperature resistance, i.e., it does not survive during thermal parent body metamorphism. Given its primitive status, Ryugu is probably the place where P7 could be preserved. Aqueous alteration does not seem to affect the P7 carrier phase significantly. The fact that this component is not present in all analysed Hayabusa2 samples can be explained by the sample’s heterogeneity due to the differences in their thermal history associated with impact events, which may appear on a very local scale. We believe that sooner or later, P7 must be identified in other Ryugu samples if noble gas studies in them continue.

On the three-isotope diagram (³⁶Ar/¹³⁰Xe vs. ¹³⁶Xe/¹³⁰Xe) the compositions of P7, P1 and SW form a trend indicating that element and isotope ratios in the components are positively correlated with each other (Fig. 6), i.e., the higher their enrichment by heavy elements the higher the enrichment of their isotopic compositions by heavy isotopes relative to SW composition. This may indicate that the processes resulting in formation of P1 and P7 noble gas components are similar. Since ions in SW have the same velocity, the heavier the mass the higher the ion energy. During implantation this results in different implantation ranges for element and isotopes of different masses and thus produces element and isotope fractionation in solids where the ions are implanted, i.e., Q phase grains, if their grain sizes are comparable with implantation ranges³⁰. This happens because a larger fraction of heavy ions goes through without stopping inside the grains, compared to that of the lighter ions. However, the direction of fractionation in this case (depletion of heavy gases and isotopes relative to the SW composition) is opposite to what is observed in P1 and P7. Thus, P1 and P7 do not represent fractionated SW components as a result of its direct implantation into Q grains.

Correlation between the difference in the elemental composition of P1 noble gases from that in SW with FIP (first ionization potential)³ indicates that ionization is an important factor during the formation of the component. This is also true for P7. Among a number of different laboratory experiments aimed at reproducing the capture of noble gases in Q, the most promising are those in which ionized noble gases are trapped at low energy in a continuously growing surface³² or organic compounds³³. To a certain extent, these experiments can reproduce the observed element and isotope fractionation in P1. These experiments are related to the processes in the protoplanetary disk with solar rather than SW starting composition, i.e., the composition of the solar photosphere. During the formation of SW in the solar atmosphere it is mass fractionated relative to the composition in the outer convection zone and photosphere. According to the Inefficient Coulomb drag (ICD) model and calculations based on the correlation between fast and slow SW isotopic compositions with He/H ratio³⁴, Ne becomes slightly isotopically lighter in SW compared to solar photosphere (13.9 vs. 13.4 for ²⁰Ne/²²Ne ratio). For Xe, the solar photosphere isotopic composition was also estimated using the ICD model²⁷. Compared to the photosphere, the elemental ratios in SW are fractionated in the opposite to the isotope fractionation direction since element ratios depend on the element’s FIPs, which are higher for the lighter noble gases when compared to heavier ones³¹, while isotope fractionation depends on ion masses. The range for solar composition is shown in Fig. 6. Thus, if carriers of P1 and P7 (Q phase) have been formed in the protoplanetary disk or protosolar molecular cloud, element and isotope fractionation during their formation should follow the directions as shown with arrows in Fig. 6, i.e., P1 is slightly or not at all fractionated in isotopic composition and strongly by elemental composition, while P7 is strongly fractionated by both isotopic and elemental compositions relative to solar composition.

Тhere remain, however, the following questions: a) Why does P7 have a different degree of fractionation compared to P1? b) What does the difference in the degree of fractionation for P1 and P7 mean in terms of the fractionation mechanism and formation of their carrier(s)? As discussed above, Xe-P7 is very rare and therefore does not contribute significantly to the Xe budget in meteorites but provides clues to the origin of Xe-P1, since the formation of both involves mass fractionation processes of varying degrees. To reveal the clues, the above questions need to be answered. However, first, the presence of P7 has to be confirmed in other Ryugu samples (material from the Bennu asteroid, which will soon be available for laboratory studies, is another potential source of the component). After that, in order to understand the chemical nature of the P7 carrier it will be important to establish its reaction with acids or other solvents.

Finesse mass spectrometry system

Bulk samples were analysed using a Finesse mass spectrometric complex designed at the Open University^35,36. The main feature of this instrument is the possibility to analyse simultaneously the isotopic compositions and contents of several elements (He, Ne, Ar, Xe, N, and C) extracted from a single sample. It consists of two magnetic sector mass spectrometers with a radius of 12 cm and one quadrupole mass spectrometer all connected to a common extraction system. All mass spectrometers are operated in a static vacuum mode. One of the magnetic sector mass spectrometers is used for the analysis of carbon in the CO₂ form; the other, for molecular N and Ar; and the quadrupole spectrometer, for He, Ne, and Xe. Gases are released by heating the sample in a double-vacuum furnace with an inner sample quartz glass tube, an outer corundum tube (the space between which is pumped out to forevacuum) and a silicon carbide heater allowing heating up to 1450^oC. Pure oxygen generated by heating CuO to 850^oC is used for oxidation, and the unused portion of oxygen is resorbed by copper oxide at 450^oC. The oxygen pressure during oxidation is 5–10 mbar, and the combustion time is 0.5 h.

The released gases are separated into the He + Ne, CO₂ + Xe, and Ar + N₂ fractions using cryogenic traps (a glass finger for sorption of CO₂ + Xe, a cold finger with molecular sieves for sorption of N₂ and Ar, while He and Ne remain in the gas phase) and additionally purified on Al–Ti getters (for noble gases) and additional copper oxide (for nitrogen). Each of the CO₂ + Xe and Ar + N₂ fractions is then subdivided into two approximately equal portions and used for the analysis of individual elements after purification. All the volumes of the vacuum system were calibrated, so the proportion of the total amount of a gas included in one or another fraction is precisely known. The amount of the released CO₂ is determined by pressure measurements using a capacitance manometer Baratron™ with a precision better than 1%. Before introduction into the mass spectrometer, CO₂ is, if necessary, additionally split up to avoid exceeding the maximum permissible signal of the mass spectrometer amplifier. This is achieved by the calibration of the volumes in which gases are split and the determination of the mass spectrometer sensitivity. A similar procedure of nitrogen splitting is also applied and is based on the preliminary measurement of its amount in a small (5%) fraction using the quadrupole mass spectrometer in which sensitivity is also calibrated with reference gas. The mass spectrometers for N₂ and CO₂ are equipped with three collectors set for masses of 28, 29, and 30 and 44, 45, and 46, respectively. The measurement itself takes approximately one minute, during which ~ 300 data points were collected for each isotope that eventually provides a precision of 0.3–0.5‰. During measurements in a static vacuum mode, CO₂ is rapidly (half-life of ~ 20 s) transformed to CO; therefore, longer measurements are impracticable. The nitrogen signal also decreases during mass spectrometric measurements, although much slower than that of CO₂. For the calculation of d¹³C and d¹⁵N, appropriate standards were measured alternately with the samples. To provide identical conditions for both measurements, the amount of the standard must correspond to that of the sample. For this purpose, a sampling system, in which standard gas is continuously bleeding from a reservoir through a capillary, is used. The pressure in the reservoir is about 3 bars to provide viscous flow. The necessary amount of gas is collected by setting the time of its accumulation in a certain volume. This technique provides highly accurate (< 2%) correspondence between the amounts of sample and standard gases during measurements. Since isotope fractionation may occur in gas flow through the capillary, the standards are calibrated using either NBS standards (calcite for CO₂) or atmospheric nitrogen (for N₂) taken from fixed a volume gas pipette system. In addition, gas flow rate is determined for all sampling systems of standards for determination of the sensitivity of mass spectrometers and the amounts of gas (nitrogen and noble gases) using the peak height method. The sampling system for noble gas standards (air) is similar and also calibrated in an appropriate manner.

The system described above is fully automated. For sample measurements, temperature and time of oxidation at each temperature step, the number of steps, and the list of elements (e.g., C, N, and Ar) are set. A 2–5 mg sample is loaded into a Pt foil (25 µm thick) capsule. The sample is dropped into an extraction furnace through a gate valve and heated at 100-200^oC for at least 0.5 h (the first step of oxidation was always conducted at the same100-200^oC to further decrease atmospheric contamination), and the analysis is further conducted in automated mode. Pneumatically controlled valves are used in the vacuum system, and cryotraps are cooled by pumping vapour of liquid nitrogen through a small cylinder jacket placed directly adjacent to a cold finger, which has a good thermal contact with it. Cryotraps are equipped with a wire heater wound directly around the cold finger between it and the cooling jacket. The duration of the autonomous operation of the instrument during sample analysis depends on the volume of the liquid nitrogen Dewar. A 50-L Dewar is sufficient for continuous operation over 24 h. During this time, 10–15 separate temperature fractions can be analysed depending on the set of elements analysed. The system blank was determined by the analysis of empty Pt foil. Since amounts of gases in the blank depend on the temperature, the blank experiments usually include a number of steps in the temperature range as for samples with however a lower temperature resolution.

Sample preparation and loading into the Finesse system.

The Ryugu samples we analysed are fine-grained aggregates as shown in Fig. S1. They were loaded into the vacuum system of Finesse without contact with the atmosphere. For that we used a glove box filled with pure nitrogen. The microbalance for the determination of sample weight was accommodated in the glove box. The sealed containers with the Hayabusa2 samples were opened in the glove box. After putting the sample aliquot into a Pt capsule whose weight was determined before, the capsule was sealed (not vacuum-tight) and weighed again. Then the sample in Pt foil was transferred into a manifold via a portable gate valve again within the glove box. After closing the gate valve, the manifold was transferred to the Finesse lab and connected to the Finesse vacuum system so that the sample could be dropped into the extraction furnace through the gate valve after pumping.

Xe isotope analysis on quadrupole mass spectrometer

For Xe isotope measurements we used Hiden Analytical quadrupole mass spectrometer (HAL 8 RC PIC-RGA 301#14168). The measurements were performed in static vacuum mode with Ti-Al getter connected to the mass spectrometer chamber to maintain the static mode. The mass spectrometer mass resolution was set to completely resolve Xe masses without any tails on the neighbouring masses (Fig. S2). At this resolution, Xe masses are not resolved from hydrocarbons. However, the contribution of hydrocarbons is practically insignificant even at Xe signals that are two orders of magnitude smaller than in the case of the analysis of the C0209 sample, which can be judged from the signals at masses 135 and 137, where the Xe signal is absent.

Peak jumping and ion counting were used to collect the data during 400 scans with 300 ms integration time and 100 ms between measurements at each peak. This took about 15 min to complete measurement. During this time, Xe signal slightly decreases, but by no more than 10% (Fig. S3). We measure only the 6 most abundant isotopes: from ¹²⁹Xe to ¹³⁶Xe. At signal rate of ~ 10⁴ cps, as was observed during C0209 sample analysis, precision at permil level can be achieved for Xe isotope ratios. Mass discrimination of the mass spectrometer for Xe is about 6.4‰/AMU with depletion of heavy isotopes (Fig. S4), it remains stable at constant mass spectrometer settings and does not depend on the signal intensity within more than two orders of magnitude. We check this by analysing variable amounts of air Xe in the range comparable with that measured during run of the C0209 sample (Fig. S5). In other words, the variations in the isotope ratios during measurements of the sample with very high Xe concentrations cannot be explained by variations in the mass discrimination on the amount of Xe in the mass spectrometer.

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A new primordial noble gas component in the solar system discovered in Ryugu asteroid

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Abstract

Figures

Introduction

Results

Noble gas concentrations and relative abundance

Isotopic composition of Xe in C0209

Discussions

Comparison of Xe-X with other primordial components

Origin of Xe-X

Methods

Finesse mass spectrometry system

Xe isotope analysis on quadrupole mass spectrometer

References

Additional Declarations

Supplementary Files

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