# Noble gases and nitrogen in material from asteroid Bennu

B. Marty, L. Zimmermann, E. Füri, D. Bekaert, J. Barnes, A. Nguyen, H.

Connolly, D. Lauretta

► To cite this version:

B. Marty, L. Zimmermann, E. Füri, D. Bekaert, J. Barnes, et al. Noble gases and nitrogen in material from asteroid Bennu. Meteoritics and Planetary Science, 2025, 10.1111/maps.70058. hal-05336135

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# Noble gases and nitrogen in material from asteroid Bennu

B. MARTY (1), L. ZIMMERMANN¹, E. FÜRİ¹, D. V. BEKAERT¹, J. J. BARNES (2), A. N. NGUYEN (3), H. C. CONNOLLY3,4,5, and D. S. LAURETTA²

¹CNRS, CRPG, UMR 7358, Université de Lorraine, Nancy, France

²Lunar and Planetary Laboratory, The University of Arizona, Tucson, Arizona, USA

³ARES (Astromaterials Research and Exploration Science), NASA Johnson Space Center, Houston, Texas, USA

⁴Department of Geology, Rowan University, Glassboro, New Jersey, USA

⁵Department of Earth and Planetary Science, American Museum of Natural History, New York, New York, USA

*Correspondence

B. Marty, CNRS, CRPG, UMR 7358, Université de Lorraine, Nancy, France.

Email: bernard.marty@univ-lorraine.fr

*(Received 23 May 2025; revision accepted 17 September 2025)*

**Abstract**–We report the elemental and isotopic abundances of all stable noble gases (helium, neon, argon, krypton, and xenon) in eight particles from asteroid Bennu returned by NASA’s OSIRIS-REx mission. We also report nitrogen abundances and isotopic ratios that were analyzed alongside neon and argon in four additional Bennu particles. These analyses confirm the similarities of Bennu material with Ivuna-type carbonaceous (CI) chondrites. The nitrogen isotopic compositions show intra- and inter-particle variations, pointing to the heterogeneous distribution of various N-bearing phases, while the abundances of nitrogen are within the range of those measured in CIs. Noble gas data indicate mixing between Q-like noble gases (a ubiquitous noble gas component found in most classes of primitive meteorites, presumably formed by noble gas incorporation into organic materials within the ionized regions of the parent cloud or in the protoplanetary disk) and various presolar components originally hosted by refractory grains that survived the high enthalpy birth of the solar system. The noble gases also include secondary contributions of three types: (i) noble gas isotopes produced by radioactivity, (ii) solar wind implantation, mostly identified in the light noble gas (He and Ne) isotopic compositions, and (iii) cosmogenic noble gases produced by interaction with high-energy cosmic rays, permitting us to estimate how long fresh surfaces were irradiated. We find that cosmic ray exposure (CRE) durations of Bennu material vary mostly between 1 and 3 Ma. These CRE ages are consistent with (i) radionuclide studies suggesting surface exposure for 2–7 Ma, (ii) small crater retention ages of 1.6–2.2 Ma, and (iii) the 1.75 ± 0.75 million years that Bennu is estimated to have been dynamically decoupled from the asteroid belt. In contrast to CRE ages, we find a maximum duration of solar wind irradiation of ≤100,000 a, in agreement with exposure duration of <85,000 a from solar energetic particle tracks and microcrater densities. The noble gas abundances in Bennu and Ryugu samples are higher by a factor ≥2 compared to CI meteorites, whereas their isotopic compositions are similar. This difference between material sampled directly from asteroids and their meteoritic equivalent suggests degradation of the latter through contact with the terrestrial environment. Neon-argon variations point to a potential genetic relationship between Bennu, Ryugu, CI materials on the one hand, and the terrestrial atmosphere on the other.
INTRODUCTION

The solar system formed from the collapse of a
molecular cloud core consisting of leftover material
from previous generations of stars. Unraveling the
composition of primitive material formed in the nascent
solar system is of primary importance for investigating
the origin and evolution of terrestrial planets, including
their inventories of volatile elements such as H, C, N, and
noble gases (Broadley et al., 2022). Carbonaceous
chondrites are rich in volatiles (e.g., H, C, N), making
them a potential source for the delivery of volatiles to
Earth and other inner planets (Alexander et al., 2012;
Marty, 2012). The chemical composition of CI
carbonaceous chondrites is close to that of the solar
photosphere, unlike those of other meteorites, which are
chemically fractionated (Anders & Grevesse, 1989).
However, even in CI chondrites, the abundances of
highly volatile elements (H, C, N, noble gases) are
drastically depleted relative to their solar abundances,
and they have distinct isotopic compositions from those
of the protosolar nebula. These differences are likely the
result of processes that occurred before or during
the condensation of solar system materials (e.g., Broadley
et al., 2022, and references therein). Furthermore,
processing on the parent bodies, such as thermal
metamorphism, aqueous alteration, and impacts,
profoundly modified the mineralogy of meteorites.

Unlike CIs and other meteorites found on Earth,
samples delivered to Earth by spacecraft have suffered
minimal interaction with the terrestrial environment,
making them ideal for investigating the link between
primitive material and planets. On 24 September 2023,
NASA's Origins, Spectral Interpretation, Resource
Identification, and Security—Regolith Explorer (OSIRIS-
REx) spacecraft returned 121.6 g of regolith material from
near-Earth asteroid (101955) Bennu (Lauretta et al., 2024).
Reflectance spectra of this B-type asteroid suggested that it
is rich in volatile elements (Clark et al., 2011). Bennu is a
rubble pile asteroid which formed from fragments resulting
from the disruption of a larger body (>100 km) (Bottke
et al., 2015) and is estimated to have been dynamically
decoupled from the main asteroid belt for 1.75 ± 0.75
million years (Ballouz et al., 2020). The returned samples
consist of clay minerals (phyllosilicates), carbonates,
magnetite, sulfides, phosphate, organic compounds, rare
high-temperature anhydrous minerals (Connolly et al.,
2025; Lauretta et al., 2024), and a suite of evaporite
minerals including sulfates, chlorides, and fluorides
(McCoy et al., 2025). Like primitive material from the
carbonaceous asteroid Ryugu delivered to Earth in 2020
by JAXA's Hayabusa2 mission (Tachibana et al., 2022;
Yokoyama et al., 2023), Bennu material presents strong
similarities with the CI chondrite group (Barnes

et al., 2025; Connolly et al., 2025; Lauretta et al., 2024). Barnes et al. (2025) presented an overview of the chemical and isotopic composition of Bennu material, including some of the volatile elements (C, N, noble gases). They concluded that Bennu's parent body formed from a similar, but not identical, mixture of materials as the CI chondrites and Ryugu.

Here, we report the results of detailed analyses of all
noble gases in eight particles, and of N, Ne, and Ar in
four different particles, picked from a sample of
aggregate Bennu material (loose, unsorted particles
<0.5 cm in length). These new data allow us to scrutinize
the composition of this previously unsampled CI-like
material, as well as the irradiation history of Bennu
regolith. Noble gases (helium, neon, argon, krypton, and
xenon) are physical tracers of the stellar heritage from the
parental molecular cloud as well as processes that led
to the formation and irradiation of the first solids (Ozima
& Podosek, 2002; Pepin, 1991; Wieler, 2002). In
carbonaceous meteorites (Krietsch et al., 2021; Mazor
et al., 1970; Okazaki et al., 2023; Ott, 2014), the major
sources of noble gas isotopes are (i) presolar components
hosted by stardust (labeled P3, P6, HL, N, G, R; Huss &
Lewis, 1994; Ott, 2014); (ii) an ill-defined phase composed
of, or showing affinities with, organic matter—the
so-called phase Q (also labeled P1 in the literature)—
which dominates heavy noble gases (Ar, Kr, and Xe;
Busemann et al., 2000); (iii) solar wind (SW) ions, which
are solar ions accelerated by the Sun's open magnetic
field lines and that are implanted into planetary surfaces;
their concentration depends on the irradiation history of
surface material, either at the surface of the parent body
or during the transit of meteoroids in space (Wieler,
1998), and (iv) noble gas isotopes produced by nuclear
reactions including radioactivity (e.g., <sup>40</sup>Ar, <sup>129</sup>Xe,
<sup>131</sup>-<sup>136</sup>Xe) and/or spallation and neutron capture
reactions induced by cosmic ray irradiation. The
simultaneous determination of all noble gas abundances
and isotopic ratios provides an unprecedented view into
the origin of Bennu material and the processes that
affected this asteroid and its original parent body.

Unlike noble gases, nitrogen can be chemically active
in forms other than the strongly bound N₂ molecule.
Because it can be analyzed together with noble gases by
static mass spectrometry, it is included in this study. This
element has two stable isotopes, <sup>14</sup>N (99.64%) and <sup>15</sup>N
(0.35%), whose ratio shows large variations among solar
system reservoirs and objects (e.g., Füri & Marty, 2015
and references therein). Although interactions with
cosmic rays can produce relative enrichments in <sup>15</sup>N
("Nitrogen" section), most isotope variations are due to
mixing between different endmember compositions
predating the formation of asteroids. The combined
analysis of nitrogen and noble gases in the same sample
<table><caption>TABLE 1. Sample ID, mass and number of extraction steps.</caption><thead><tr><th>Sample ID</th><th>Mass (mg)</th><th>Extraction (steps)</th></tr></thead><tbody><tr><td colspan="3">All noble gas analysis</td></tr><tr><td>OREX-803036-0</td><td>0.5313</td><td>3</td></tr><tr><td>OREX-803037-0</td><td>0.1792</td><td>2</td></tr><tr><td>OREX-803038-0</td><td>0.0952</td><td>2</td></tr><tr><td>OREX-803039-0</td><td>0.1190</td><td>5</td></tr><tr><td>OREX-800032-105</td><td>1.4420</td><td>8</td></tr><tr><td>OREX-800032-107</td><td>0.1350</td><td>2</td></tr><tr><td>OREX-800032-108</td><td>0.3312</td><td>2</td></tr><tr><td>OREX-800032-109</td><td>0.1519</td><td>2</td></tr><tr><td colspan="3">Ne, Ar, N analysis</td></tr><tr><td>OREX-803032-0</td><td>0.2246</td><td>15</td></tr><tr><td>OREX-803033-0</td><td>0.0343</td><td>5</td></tr><tr><td>OREX-803034-0</td><td>0.1578</td><td>13</td></tr><tr><td>OREX-803035-0</td><td>0.1008</td><td>11</td></tr></tbody></table>

and even during the same extraction step provides a powerful means to investigate the origin(s) and evolution of asteroidal material (Broadley et al., 2023; Gamblin et al., 2024; Okazaki et al., 2023).

## SAMPLES AND ANALYTICAL METHODS

Aggregate material was collected from within the OSIRIS-REx spacecraft's Touch-and-Go Sample Acquisition Mechanism (TAGSAM; Bierhaus et al., 2018) and handled in the curation facility at NASA's Johnson Space Center (Righter et al., 2023) in November 2023. Aggregate sample OREX-800032-100 was sent to the Centre de Recherches Pétrographiques et Géochimiques (CRPG), Nancy, France, to perform the noble gas and nitrogen analyses reported here. We handpicked the 12 particles for our analyses in an ISO6 cleanroom. The sample IDs and masses of the individual particles are given in Table 1. Individual particles were weighed using a Mettler Toledo XPR2U™ microbalance, which is not operated under a controlled atmosphere for stability reasons. Hence, the particles were briefly exposed to air. The particles were then placed into different pits of a ZnSe-windowed laser chamber, which was gently baked at 100°C and pumped down to a pressure of $10^{-9}$ mbar overnight (Gamblin et al., 2024). Each particle was heated under vacuum using a 10.6 µm CO$_2$ laser (MIR$^2$, Elemental Scientific™), with the laser power gradually increased from 1 to ~50% of the total 32 W output until the particles completely melted. A high-resolution CCD video camera positioned above the laser chamber allowed for the monitoring of sample heating and melting. At each heating step, released gases were purified and cryogenically separated.

A Thermo Scientific Helix MC$^{+}$™ noble gas mass spectrometer was used for the analysis of all noble gases

(He, Ne, Ar, Kr, Xe; Broadley et al., 2023) in eight particles. Samples were laser-heated for 3–7 min, then evolved gases were purified onto hot getters. Kr and Xe were trapped onto a glass finger held at 77 K, then Ar was trapped onto a charcoal trap held at 77 K. The remaining He + Ne fractions were purified onto further getters. Ne was trapped in a cryotrap containing a charcoal grain held at 40 K. Helium was analyzed first, then Ne was desorbed from the cryotrap at 90 K and analyzed. Argon trapped in the cold glass finger was desorbed at room temperature and analyzed. Xe and Kr were desorbed from the glass finger and sequentially analyzed (Xe first, Kr second). Argon and Ne isotopes were analyzed in multicollection mode, and He, Kr, and Xe were analyzed in monocollection mode using Faraday collector and electron multipliers. The system was calibrated with aliquots of atmospheric noble gases (Ne, Ar, Kr, Xe) and an international He isotope standard (Matsuda et al., 2002). Procedural blanks, repeated all along the four-month analysis sequence, were $3.6 \pm 1.1 \times 10^{-18}$ mol $^{22}$Ne, $1.8 \pm 0.1 \times 10^{-17}$ mol $^{36}$Ar, $1.9 \pm 0.1 \times 10^{-18}$ mol $^{84}$Kr, and $3.4 \pm 0.4 \times 10^{-19}$ mol $^{130}$Xe. The $^3$He blank was below the detection limit. Stepwise heating was applied in an attempt to identify different noble gas components depending on the retentivity of their host phases. The number of steps depended on the quantity of gas and therefore the available mass of the sample (Table 1). He, Ne, Ar, Kr, and Xe data are reported in Marty (2025) and in Supporting Information S1 together with more detailed information about the analytical procedure.

A Nu Instruments Noblesse-HR™ noble gas mass spectrometer was used for multicollection analyses of N, Ne, and Ar extracted from four particles (Table 1) (see Gamblin et al., 2024 and Zimmermann et al., 2025, for details of the analytical procedure). $\delta^{15}$N ($^{29}$N$_2$/$^{28}$N$_2$), $^{20,21}$Ne/$^{22}$Ne, and $^{36}$Ar/$^{38}$Ar are reported for heating steps with <40% blank contributions; $^{40}$Ar was below the detection limit for most steps. N-Ne-Ar data are reported in Füri (2025) and in Supporting Information S2 together with more detailed information about the analytical procedure.

## NOBLE GASES AND NITROGEN

### Noble Gas Abundance Pattern

The noble gas abundances of the eight particles, normalized to the solar wind composition (Ott, 2014) and to Xe, are compared to the composition of Phase Q (Busemann et al., 2000) in Figure 1. Notably, we did not detect the so-called P7 component, an extremely fractionated, Xe-rich phase previously observed in a Ryugu particle (Verchovsky et al., 2024). Helium and
<figure><img src="image_2.png" /><figcaption>FIGURE 1. Relative abundances of noble gases (He, Ne, Ar, Kr) in eight Bennu particles, normalized to Xe and to the solar wind (SW) composition. The SW and Q (brown dots) compositions are from Busemann et al. (2000) and Ott (2014), respectively, and references therein.</figcaption></figure>

neon in excess of Q require contributions from additional
host phases such as implanted solar gas and multiple
presolar components (see “Helium, Neon, and Argon
Isotopes” section). Sample OREX-800032-105 (dark blue
diamonds) is further enriched in $^4$He and $^{20}$Ne by one
order of magnitude. These enrichments are likely due to
contributions of solar noble gases, as confirmed by bulk
$^3$He/$^4$He and $^{20}$Ne/$^{22}$Ne ratios of $3.37 \times 10^{-4}$ and 12.70,
respectively, close to solar wind ratios of $4.64 \times 10^{-4}$ and
13.8, respectively (Ott, 2014). For the other samples
which have more CI-like Ne isotope ratios, the fraction of
Q-Ne in the average composition of the samples is
$14.0 \pm 4.1\%$ (1$\sigma$), consistent with the fraction observed
in the CI chondrite Orgueil (12.4%; Ott, 2014). The
remaining Ne is contributed by presolar phases, including
~60% Ne-HL as inferred from the isotopic composition
of neon (discussed later).

Noble Gas Abundances

The bulk noble gas abundances of Bennu particles,
normalized to their respective masses, are among the
highest recorded in carbonaceous chondrites (Figure 2).
All Bennu and Ryugu samples analyzed so far show Ar
and Xe contents at least ~2 times higher than in CIs,
attesting to the excellent preservation of pristine noble
gases in samples returned by spacecraft. This suggests the
noble gas host phases for meteoritic samples degrade
during atmospheric entry and/or during the subsequent
residence time in the terrestrial environment.

Both Ryugu and Bennu have mean $^{36}$Ar/$^{130}$Xe ratios
(Ryugu: $435 \pm 98$, n = 14; data from Broadley et al.,
2023; Okazaki et al., 2023; Bennu: $447 \pm 91$, n = 8, this

<figure><img src="image_3.png" /><figcaption>FIGURE 2. Absolute abundances of Ar and Xe in Bennu, Ryugu, and CI and CM meteorites. Bennu data are from this work, Ryugu data are from Okazaki et al. (2023) and Broadley et al. (2023), CI data are from Mazor et al. (1970), Nagao et al. (1984), King et al. (2019), Krietsch et al. (2021), CM data are from numerous works compiled in Schultz and Franke (2004). Newly analyzed samples from Krietsch et al. (2021) include variably aqueously altered CM and related carbonaceous chondrites. Error bars represent 1 standard deviation (1σ). The light green shaded area represents the Q $^{130}$Xe/$^{36}$Ar ratio of 469 ± 29 (Busemann et al., 2000). The CIs are represented by the Alais, Ivuna, Orgueil, and Tonk meteorites using their mean concentrations from available data (King et al., 2019; Mazor et al., 1970). Data from the Paris CM meteorite are represented by open squares (CRPG: Bekaert et al., 2019) and gray squares (ETH: Krietsch et al., 2021). Discrepancies are likely the result of heterogeneities in the analyzed fragments. The mean value for Paris (large open square) is computed with CRPG data.</figcaption></figure>

work) similar within errors to the Q ratio (469 ± 29;
Busemann et al., 2000) (Figure 2). The mean $^{36}$Ar/$^{130}$Xe
ratio of CI (733 ± 112, n = 4; Krietsch et al., 2021;
Mazor et al., 1970) is, however, significantly higher than
the Q ratio. This excess could be due to the occurrence of
a $^{36}$Ar–rich phase observed in CM meteorites (Krietsch
et al., 2021) or to contamination by the terrestrial
environment, which would tend to enrich meteorites in
$^{36}$Ar relative to $^{130}$Xe because atmospheric xenon is
depleted by one order of magnitude compared to the
other noble gases (Ozima & Podosek, 2002).

In an extensive analytical survey of Mighei-type (CM)
chondrites and associated carbonaceous chondrites,
Krietsch et al. (2021) reported the occurrence of a
$^{36}$Ar-rich noble gas component, distinct from Q, in some
of the CM chondrites. This component was best observed
in CM chondrites that experienced limited aqueous
alteration, whereas the rest of the CM chondrites have
noble gas compositions closer to Q. Notably, the least
altered CM chondrites have $^{36}$Ar contents comparable to
those of Bennu and Ryugu, but their bulk ¹³⁰Xe and ⁸⁴Kr contents are lower than those of the present samples. Krietsch et al. (2021) proposed that most CM chondrites (those not presenting excesses of ³⁶Ar) could have lost an unspecified ³⁶Ar-rich phase upon aqueous alteration. CIs may record the occurrence of such a ³⁶Ar-rich phase (Figure 2), but it remains unclear whether it was initially absent or partially lost during episodes of extensive aqueous alteration that shaped the lithology of these meteorites. Alternatively, limited atmospheric contamination may be responsible for enrichments in ³⁶Ar relative to ¹³⁰Xe (Figure 2) since the ³⁶Ar/¹³⁰Xe ratio of air (9602; Ozima & Podosek, 2002) is much higher than the Q ratio (469 ± 29). Because Q noble gases can be lost upon metamorphism (for CMs, T > 500°C; Krietsch et al., 2021), the high abundance of Q noble gases precludes extensive heating, in agreement with the occurrence of anhydrous minerals (Connolly et al., 2025; Lauretta et al., 2024) and the preservation of pristine stable isotope signatures of presolar SiC grains at an abundance consistent with unheated chondrites (Barnes et al., 2025). Conversely, the comparison of bulk noble gas concentrations in CIs on the one hand and in Bennu and Ryugu samples on the other hand (Figure 2) suggests that CIs have lost a fraction of their Q noble gas load, possibly upon oxidation in the O₂-rich terrestrial environment if the missing noble gas load was trapped in organics. Indeed, phase Q gases are prone to partial loss upon oxidation (e.g., HNO₃ attack; Lewis et al., 1994). We also compare our data with those obtained for the Paris CM meteorite (Bekaert et al., 2019), which is among the least altered, least metamorphized CM chondrites (petrologic type: 2.7–2.9; Hewins et al., 2014; Marrocchi et al., 2014). The xenon content of Bennu, Ryugu, and Paris are comparable within uncertainties (Figure 2), supporting the view that those materials are among the most chemically primitive analyzed so far. However, the ³⁶Ar/¹³⁰Xe ratio of Paris is slightly higher than the Q ratio, suggesting that this meteorite may have partly preserved the ³⁶Ar-rich component seen in some of the other CMs (Krietsch et al., 2021), whereas aqueous alteration might have washed out this component from CI–like Bennu and Ryugu materials if originally present.

## Effects of Aqueous Alteration

The abundances of presolar grains in Bennu (Barnes et al., 2025) and Ryugu (Nguyen et al., 2023) samples indicate that their parent bodies did not experience extensive thermal metamorphism (i.e., temperatures in excess of ~200°C). Likewise, the high abundances of Q noble gases preclude heating above ~500°C as higher temperatures would have resulted in loss of Q gases (Busemann et al., 2000). The preservation of stable

<figure><img src="image_4.png" /></figure>

FIGURE 3. Noble gas three-element plot of Bennu, Ryugu, and primitive carbonaceous chondrites (after Broadley et al., 2023). Suffix *tr* refers to the trapped Ne component obtained after the removal of cosmogenic Ne. All carbonaceous chondrites fall along a trend-line between phase Q and presolar nanodiamond HL. The noble gas phase released from CR chondrites during interaction with water (CR water: Krietsch, 2020) has a composition trending toward HL. Data are from Mazor et al. (1970), Nagao et al. (1984), Füri et al. (2013), Krietsch (2020), Krietsch et al. (2021), Okazaki et al. (2023), Broadley et al. (2023), Barnes et al. (2025), Glavin et al. (2025) and references therein. Presolar P3 composition is from Ott (2014). Note that the contribution of solar wind Ne rich in ²²Ne would shift the position of the data points toward the lower left (³⁶Ar/²²Ne = 1.83 × 10⁻³; ¹³⁰Xe/²²Ne = 2.57 × 10⁻⁶; data from Ott, 2014).

isotope (H, N) “hotspots” in Bennu (Barnes et al., 2025) and Ryugu (Nguyen et al., 2023; Nittler et al., 2024) further supports low temperature (≤100°C) for their parent bodies. In CI chondrites, Bennu, and Ryugu, the ubiquitous abundance of hydrated phases and the scarcity of anhydrous minerals indicate that their parent bodies experienced extensive aqueous alteration (Barnes et al., 2025; Connolly et al., 2025; Lauretta et al., 2024; McCoy et al., 2025; Nguyen et al., 2023).

Aqueous alteration appears to result in the preferential loss of the water-soluble noble gas phase(s) rich in Ar relative to Kr and Xe (Krietsch et al., 2021). In Figure 3, we use a similar noble gas three-element plot for Bennu, Ryugu, and primitive carbonaceous chondrites as in Broadley et al. (2023). Aqueous alteration results in the progressive loss of the water-soluble components, represented by CR water (Krietsch, 2020), while Q noble gases are mostly preserved. Hence, Bennu, Ryugu, and CI chondrites contain less of this water-soluble component than some of the CM chondrites, consistent with their higher level of aqueous alteration. Therefore, the effect of aqueous alteration results in an increase of
both ($^{130}$Xe/$^{22}$Ne)tr and ($^{36}$Ar/$^{22}$Ne)tr ratios (where suffix tr refers to trapped Ne, that is, corrected for the contribution of cosmogenic Ne) (Figure 3). Bennu and Ryugu samples have Q-like Ar, Kr, and Xe elemental and isotopic ratios and do not show the occurrence of the putative $^{36}$Ar-rich component (Figure 2). In addition, they contain among the highest heavy noble gas abundances when compared to the carbonaceous chondrites (Figure 2). This suggests that, if their parent bodies experienced extensive aqueous alteration removing the soluble $^{36}$Ar-rich noble gas carrier, this process preserved their high abundance of Q noble gases. It remains to be seen whether the putative $^{36}$Ar-rich component ever existed in the CI-like parent bodies. Notably, Bennu samples are, on average, closer to the Q endmember than the Ryugu and CI samples, suggesting that, if the trend displayed in Figure 3 is related to increasing loss of the water-soluble component, Bennu's parent body may have experienced more extensive aqueous alteration than Ryugu's. This scenario would, however, contradict the better preservation of stable isotope anomalies in Bennu samples compared to those from Ryugu (Barnes et al., 2025).

## Noble gas Isotopes: Searching for the Origins

### Xenon

Noble gas isotopes that are not produced by nuclear reactions in meteorites and their parent bodies provide a useful means to investigate the multiple origins of primitive material. In carbonaceous chondrites, particularly in CI, the heavy noble gases—Ar, Kr, and Xe—are dominated by the Q component, with contributions from presolar noble gases. Xenon is of particular interest due to the multiplicity of its isotopes. Here, we examine the composition of Xe in both whole particles and step-heating fractions. Figure 4 compares the weighted mean Xe isotope composition of particles with masses ranging from 0.0952 to 0.5313 mg with particle OREX-800032-105 (mass = 1.442 mg). The mass of the latter particle was higher than those of the other seven particles, permitting the analysis of a higher amount of gas and, therefore, a better precision. Conversely, the seven smaller particles illustrate the diversity and intrinsic heterogeneity of sampled particles. Data are given in per mil relative to Q-Xe (Busemann et al., 2000), with uncertainties as $1\sigma$. Both sets of data show a similar Xe isotope pattern, which appears to be an intrinsic property of Bennu samples and not the result of a random contribution of exotic components. Both Xe isotope spectra are comparable within uncertainties, showing significant deviations from Q. We observe a monoisotopic excess in $^{129}$Xe (arguably from the decay of short-lived $^{129}$I; $T_{1/2}$ = 16 Ma) along with enrichments in the heavy $^{134-136}$Xe isotopes. The Xe

<figure><img src="image_5.png" /></figure>

FIGURE 4. Comparison of the error-weighted mean bulk Xe isotopic composition of seven particles (OREX-803039-0, OREX-803038-0, OREX-803037-0, OREX-803036-0, OREX-800032-107, OREX-800032-109, OREX-800032-108) with that of particle OREX-800032-105. The mass of the latter particle (1.442 mg) was higher than those of the other seven particles (0.0952-0.5313 mg), permitting the analysis of a higher amount of gas and, therefore, a better precision. Conversely, the seven smaller particles illustrate the diversity and intrinsic heterogeneity of sampled particles. Data are given in per mil relative to Q-Xe (Busemann et al., 2000), with uncertainties as $1\sigma$. Both sets of samples present comparable Xe isotope spectra, with enrichments in $^{129}$Xe and $^{131-136}$Xe compared to Q. The heavy isotope enrichments may trace the contribution of presolar Xe-HL (a presolar component rich in light (L) Xe isotopes and heavy (H) Xe isotopes) but are not accompanied by correlated enrichments in the light isotopes $^{124}$Xe and $^{126}$Xe. A similar pattern is observed in Ryugu samples (Broadley et al., 2023).

isotopic spectra do not show the depletion in $^{134-136}$Xe that characterizes Xe analyzed in the coma of Comet 67P/Churyumov-Gerasimenko (67/C-G) (Marty et al., 2017). The potential genetic link between comets and Bennu (and Ryugu; Broadley et al., 2023) thus remains to be seen. We cannot exclude the possibility that a limited contribution of cometary Xe to the Bennu parent body caused a relative depletion in its heavy Xe isotopes, which could have been overprinted by the addition of $^{131-136}$Xe from presolar material from fission. Unfortunately, the light Xe isotopes could not be analyzed in 67P/C-G (Marty et al., 2017), precluding a definitive resolution of this issue.

Excess of $^{129}$Xe due to the decay of extinct $^{129}$I (hereafter $^{129}$Xe*) provides a way to set constraints on the amount of iodine originally present in Bennu, assuming a closed system, caused by the situ decay of this short-lived isotope. Using the weighed mean of all eight particles ($^{129}$Xe* = (1.53 ± 0.97) × 10$^{-14}$ mol g$^{-1}$) and assuming an initial $^{129}$I/$^{127}$I ratio of ~10$^{-4}$ (Gilmour, 2000), we obtain an iodine content of 19 ppb (range: 7-32 ppb), comparable to an estimate of 24 ppb for Ryugu (Broadley et al., 2023), within the range of CM chondrite
values (6–65 ppb; Clay et al., 2017) but lower than the 57 ppb measured in Orgueil (Clay et al., 2017). The estimated iodine content is likely a lower limit because the calculation assumes closure of the I–Xe system at the start of solar system formation. If we instead use the measured $^{127}$I concentration of 57 ppb from Orgueil, the closure time (the time interval after which $^{129}$Xe became trapped in solids) would be 25 Ma. Whether higher values proposed for CIs (up to 530 ppb I; Lodders et al., 2009) are compromised by terrestrial contamination remains to be investigated. Direct measurements of halogens in Bennu will pave the way for high-precision I–Xe dating.

Excesses in heavy Xe isotopes relative to Q have been reported in carbonaceous chondrites, particularly in CIs (Mazor et al., 1970). These excesses may have two different origins: (i) fission of extinct $^{244}$Pu ($T_{1/2}$ = 82 Ma) and extant $^{238}$U ($T_{1/2}$ = 4450 Ma), or (ii) the presence of presolar HL, rich in both light and heavy Xe isotopes (Reynolds & Turner, 1964). Here, we test the first possibility by computing the expected amount of fisiogenic Xe ($Xe_f$) that would have accumulated over 4.5 Ga since the accretion of Bennu's parent body. Using the U content reported for Bennu material (10 ppb; Lauretta et al., 2024), the canonical $^{244}$Pu/$^{238}$U ratio of 0.0068 for the nascent solar system (Hudson et al., 1989), and the respective fission yields of these radionuclides (Ozima & Podosek, 2002), we calculate that fission would have produced $2.1 \times 10^{-17}$ mol g$^{-1}$ of $^{136}$Xe$_f$ over the age of the solar system. Given the observed $^{136}$Xe excess relative to Q (weighted mean: $8.2 \pm 3.0 \times 10^{-15}$ mol g$^{-1}$), we conclude that fission could have produced less than 3% of the observed $^{136}$Xe excess. Note that the contribution of $^{136}$Xe$_f$ to the observed $^{136}$Xe excess would be even lower if cometary Xe contributed to Bennu material. Hence, we conclude that the $^{131-136}$Xe excesses may rather be attributed to the presence of presolar Xe–H in Bennu material. The contribution of Xe–HL to the total Xe is computed to be ~2.1% from the excess of $^{136}$Xe relative to Q, which compares well with estimated values for Orgueil (1.5%; Ott, 2014), Paris CM (1.8%; Bekaert et al., 2019), and Ryugu material (2.7%; Broadley et al., 2023). However, we do not observe correlated excesses in $^{124-126}$Xe (Figure 4), which points to a discrepancy between Xe–L and Xe–H also previously observed in Ryugu (Broadley et al., 2023) and Paris (Bekaert et al., 2019). $^{124}$Xe and $^{126}$Xe are by far the less abundant Xe isotopes and therefore the most difficult ones to measure with precision. The lack of apparent excess of these light isotopes could also potentially arise from the decoupling of Xe–L and Xe–H, which are produced by distinct nucleosynthetic processes (p– vs. r–process, respectively). However, efforts to deconvolve Xe–L from Xe–H in nanodiamonds have failed so far

(Huss & Lewis, 1994). Another possibility is that the Q composition (Busemann et al., 2000) used as a reference might have been depleted in the light Xe isotopes. In three Bennu samples, $^{126}$Xe seems more depleted than $^{124}$Xe. Because both isotopes can be produced by spallation, with cosmogenic $^{126}$Xe production being higher than that of $^{124}$Xe (e.g., Hohenberg et al., 1981), one cannot exclude the possibility that the canonical Xe–Q composition incorporated some cosmogenic isotopes, artificially raising the levels of $^{124-126}$Xe and therefore masking potential excesses of these isotopes from Xe–HL. Another way to deplete light Xe isotopes relative to heavy ones is through isotope fractionation. According to Gilmour (2010), Xe–Q could have resulted from isotopic fractionation of SW. The Xe–Q composition is a mean value obtained from the analysis of several meteorites, having slightly variable Xe isotope compositions attributed to variable addition of presolar Xe to a common fractionated SW component (Supporting Information S3). A fractionated primitive Xe component, more isotopically fractionated than the canonical Xe–Q component, might have been preferentially enriched in heavy Xe isotopes compared to the light ones. Bennu samples offer the exciting possibility to access enough pristine material to obtain high precision light Xe isotope measurements.

We also investigated the presence of Xe subcomponents in the “large” particle of Bennu (OREX-800032-105, *m* = 1.442 mg), whose mass allowed for sequential analysis of released gases over a total of 8 extraction steps obtained by progressively increasing the power of the laser. This is not sensu stricto a temperature step experiment because the temperature was not known precisely, but the rationale is that noble gases with the lowest retention strength are released first. Figure 5 shows the Xe isotopic spectra of Steps #2 and #4, which show the largest isotope deviations relative to Q (with the other steps being close to Q within errors). Step #2 reveals that a large amount of $^{129}$Xe* is released at relatively low temperature, presumably from the disruption of a phase that originally hosted iodine. Such a labile phase could be related to an evaporitic sequence (sodium–bearing phosphates and sodium–rich carbonates, sulfates, chlorides, and fluorides) formed during evaporation of a late-stage brine that existed early in the history of Bennu's parent body (McCoy et al., 2025). This large $^{129}$Xe* amount is accompanied by equally large excesses of $^{131-136}$Xe isotopes, which, if resulting from fission of actinides, would be quite surprising as the putative parent isotopes $^{238}$U and $^{244}$Pu are unlikely to be soluble in brine-related phases. These excesses are associated with deficits in light $^{124-126}$Xe isotopes, however, raising the possibility that at least part of the heavy Xe isotope excesses are due to isotope
<figure><img src="image_6.png" /><figcaption>FIGURE 5. Left hand panel: Xenon isotopic ratios, expressed in per mil (‰) relative to Q Xe, of selected laser extraction steps (steps #2 and #4) of particle OREX-800032-105. Right-hand panels: Variations of the ¹²⁹Xe/¹³⁰Xe, ¹³⁶Xe/¹³⁰Xe, and ¹²⁴Xe/¹³⁰Xe across the different extraction steps. Extraction temperature increases from left to right.</figcaption></figure>

fractionation. Such fractionation might have occurred
during evaporation processes that led to the formation of
the evaporite sequence. Isotope fractionation may also
account for the apparent lack of Xe–L in the bulk sample
(Figure 4) as it might have been balanced by the deficit of
¹²⁴–¹²⁶Xe seen in Step 2. Xe–HL is clearly identified in the
gas released at Step #4, indicating the disruption of host
nanodiamonds at medium to high temperature (~1000 to
1600°C according to Huss & Lewis, 1994).

Helium, Neon, and Argon Isotopes

Here, we discuss the compositions of noble gases
other than Xe. Excluding cosmogenic isotopes, light
noble gases are essentially a mixture of Q, HL, other
presolar components (P3, Ne–G, Ne–H; see Ott, 2014,
and refs. therein for characterization of presolar
components), and SW. Krypton abundance is Q-like
(Figure 1), its isotopic pattern is also similar to Q, and we
do not further discuss the composition of this element.
The helium isotopic ratios (³He/⁴He) vary between the
SW ratio (4.64 × 10⁻⁴) and values comparable to or
lower than He–HL (i.e., helium released with Xe–HL)
or He–Q. Because ³He can be quantitatively produced by
galactic cosmic rays (GCR), and ⁴He is produced by the
decay of actinides, the ³He/⁴He ratio by itself is of limited
relevance for investigating sources and processes. The
error-weighted mean ³⁸Ar/³⁶Ar ratio of all steps obtained
with the Thermo Scientific MC Helix+™ and Nu
Noblesse–HR™ mass spectrometers is 0.18854 ± 0.00049
(n = 49), identical within errors to Q (0.1874 ± 0.0004;
Busemann et al., 2000; Wieler et al., 1992). Together with
Kr and Xe data for Bennu samples, this similarity
confirms that Q noble gases dominate the inventory of Ar

in CI-like material (Busemann et al., 2000; Ott, 2014;
Wieler et al., 1992).

The three neon isotopes permit better identification of
primordial components together with processes occurring
in space. The latter result from (i) the production of
isotopes by spallation reactions induced by the interaction
with GCR (or solar cosmic rays, SCR), and (ii) the
implantation of SW ions (Meshik et al., 2007; Wieler
et al., 1989). Both processes affect particles at the surface
of the airless asteroid (or possibly of the parent body), but
to different depths: the implantation of SW ions occurs at
the uppermost surface, within a few tens of nanometers,
whereas cosmic rays interact to depths of several cm to
tens of cm. In a neon three-isotope diagram (Figure 6),
bulk data for samples of Bennu (this work), Ryugu
(Broadley et al., 2023; Okazaki et al., 2023), CI, and CM
meteorites (Krietsch et al., 2021; Mazor et al., 1970; Nagao
et al., 1984; Schultz & Franke, 2004) plot within a domain
defined by SW, a presolar Ne component mainly hosted by
nanodiamonds, and the cosmogenic endmember. CIs also
contain Q Ne with an intermediate ²⁰Ne/²²Ne value of
10.4–10.7 (Busemann et al., 2000). In order to better define
the original Ne component(s) in Bennu, we corrected the
²⁰Ne/²²Ne ratios for the contribution of cosmic
ray-produced Ne isotopes following the method described
in Supporting Information S4. We then constructed a
distribution function based on the ²²Ne<sub>tr</sub> contents
(Supporting Information S5). The frequency distribution
points to Bennu Ne being dominated by HL and Q, with
the addition of SW Ne. In particular, sample
OREX-800032-105 is rich in SW Ne and contains large
abundances of He and Ne compared to other Bennu
samples, indicating heterogeneous SW irradiation of
<figure><img src="image_7.png" /></figure>

FIGURE 6. Neon bulk (a) and stepwise heating (b) data of Bennu samples. Endmember data are from the compilation in Ott (2014). References for Hayabusa2 and meteoritic data are given in the Figure 2 caption. Red lines represent mixing between (i) SW, (ii) pure $^{22}$Ne, a nucleosynthetic endmember hosted by presolar SiC and graphite (Ne–G,R), and (iii) GCR Ne. Stepwise heating data were obtained with either the Helix MC+ mass spectrometer, on which all noble gases were analyzed in eight particles, or the Noblesse–HR mass spectrometer, on which Ne was analyzed together with Ar and N in four different particles. Deviations of data point toward the right-hand side (high $^{21}$Ne/$^{22}$Ne) due to the contribution of cosmogenic Ne, permitting us to compute cosmic ray exposure ages.

Bennu particles. The $^{38}$Ar/$^{36}$Ar ratios are all within the range of Q ratios and do not show lower values that would indicate the presence of SW Ar ($^{38}$Ar/$^{36}$Ar = 0.1818 ± 0.0001; Meshik et al., 2014), except for the first extraction step of sample OREX-803037-0 that reveals SW Ar ($^{38}$Ar/$^{36}$Ar = 0.1829 ± 0.0012) together with SW Ne (($^{20}$Ne/$^{22}$Ne)tr = 12.97 ± 0.21). Some of the stepwise heating data points lie below the HL-GCR mixing line, pointing to potential contributions of presolar Ne rich in Ne–G produced in giant asymptotic branch stars and Ne–R from the decay of short-lived $^{22}$Ca. These exotic Ne components, observed in most carbonaceous chondrites, are hosted in presolar SiC and graphite, respectively (Huss & Lewis, 1994).

## Irradiation History

In all classes of regolithic meteorites and in lunar soils, SW Ne and cosmogenic isotopes (e.g., $^{21}$Ne$_c$) are generally correlated as a result of long-term surface irradiation (Wieler et al., 1989). However, we do not observe such a correlation in the Bennu samples (Supporting Information S6), nor in the Ryugu samples (Okazaki et al., 2023). In particular, sample OREX-800032-105, which contains the highest amount of SW Ne, does not have a correspondingly high $^{21}$Ne$_c$ content (Table 2). This difference could be due to a much shorter irradiation duration compared to planetary regoliths, as well as to a recent re-distribution of Bennu material since its ejection from the main asteroid belt. Following Okazaki et al. (2023), we estimate an upper limit for the duration of SW irradiation of sample

OREX-800032-105. The mass of this sample, 1.442 mg, is converted to a volume using a mean density of 1.8 g cm$^{-3}$, which permits the estimation of a mean radius of $5.8 \times 10^{-2}$ cm, assuming a spherical geometry and a disk surface area of $1.1 \times 10^{-2}$ cm$^2$. In this case, the accumulation rate of $^4$He for this sample is $1.9 \times 10^{-15}$ mol a$^{-1}$. Considering a SW flux of $1.8 \times 10^{-13}$ mol cm$^{-2}$ a$^{-1}$ from Genesis measurements (Burnett et al., 2011) and using the bulk ($^{20}$Ne/$^{22}$Ne)tr ratio of 11.95 and the $^{22}$Ne$_tr$ content of $1.70 \times 10^{-11}$ mol g$^{-1}$, we obtain a duration of SW irradiation of about 100,000 a, which is an upper limit since part of the Ne does not derive from SW. Such duration is consistent with estimates obtained from solar energetic particle track and microcrater densities (<80,000 a; Keller et al., 2025). Based on their respective ($^{20}$Ne/$^{22}$Ne)tr ratios, other Bennu samples analyzed in this study have much lower SW irradiation durations. For comparison, sample OREX-800032-105 has a $^{21}$Ne$_c$ age of $1.97 \pm 0.76$ Ma, evidencing a decoupling between SW and GCR irradiations for this asteroid, observed otherwise also from other tracers (Keller et al., 2025).

We estimate cosmic ray exposure (CRE) ages from the amount of $^{21}$Ne$_c$ (Table 2, Supporting Information S4 for calculation), assuming a constant GCR flux, and neglecting SCR given the likely recent irradiation history of Bennu. As for Ryugu (Okazaki et al., 2023), the calculated production rate of $^{21}$Ne$_c$ at $145 \text{ g cm}^{-2}$ shielding, assuming $2\pi$ steradian exposure on a 1.2 (0.7–1.4) astronomic unit orbit, and composition from Lauretta et al. (2024), is $4.0 \times 10^{-14} \text{ mol g}^{-1} \text{ Ma}^{-1}$. The CRE ages span from 1.1 to 8.4 Ma, a range similar to that
<table><caption>TABLE 2. Cosmic ray exposure <sup>21</sup>Ne<sub>c</sub> ages.</caption><thead><tr><th>Sample ID</th><th><sup>22</sup>Ne (mol g<sup>-1</sup>)</th><th>1σ</th><th>(<sup>20</sup>Ne/<sup>22</sup>Ne)<sub>o</sub></th><th>1σ</th><th>(<sup>21</sup>Ne/<sup>22</sup>Ne)<sub>o</sub></th><th>1σ</th><th>α</th><th>(<sup>20</sup>Ne/<sup>22</sup>Ne)<sub>tr</sub></th><th>(<sup>21</sup>Ne/<sup>22</sup>Ne)<sub>tr</sub></th><th>β</th><th>T<sub>21</sub> (Ma)</th><th>1σ</th></tr></thead><tbody><tr><td>OREX-803036-0</td><td>1.52E-12</td><td>4.65E-14</td><td>9.06</td><td>0.03</td><td>0.0595</td><td>0.0006</td><td>0.62</td><td>9.43</td><td>0.0225</td><td>1.76</td><td>1.44</td><td>0.55</td></tr><tr><td>OREX-803037-0</td><td>3.00E-12</td><td>1.05E-13</td><td>9.37</td><td>0.04</td><td>0.0473</td><td>0.0006</td><td>0.96</td><td>9.62</td><td>0.0230</td><td>1.12</td><td>1.87</td><td>0.72</td></tr><tr><td>OREX-803038-0</td><td>1.68E-12</td><td>6.95E-14</td><td>9.37</td><td>0.70</td><td>0.0645</td><td>0.0015</td><td>0.54</td><td>9.80</td><td>0.0234</td><td>1.90</td><td>1.77</td><td>0.68</td></tr><tr><td>OREX-803039-0</td><td>1.62E-12</td><td>5.45E-14</td><td>8.83</td><td>0.08</td><td>0.1015</td><td>0.0020</td><td>0.27</td><td>9.64</td><td>0.0230</td><td>3.86</td><td>3.25</td><td>1.25</td></tr><tr><td>OREX-800032-105</td><td>1.71E-11</td><td>3.63E-13</td><td>11.89</td><td>0.02</td><td>0.0330</td><td>0.0002</td><td>2.50</td><td>11.95</td><td>0.0285</td><td>0.16</td><td>1.97</td><td>0.76</td></tr><tr><td>OREX-800032-107</td><td>2.34E-12</td><td>8.04E-14</td><td>10.72</td><td>0.06</td><td>0.0451</td><td>0.0009</td><td>1.06</td><td>10.95</td><td>0.0261</td><td>0.77</td><td>1.14</td><td>0.44</td></tr><tr><td>OREX-800032-108</td><td>1.52E-12</td><td>5.67E-14</td><td>7.93</td><td>0.03</td><td>0.1451</td><td>0.0014</td><td>0.16</td><td>9.13</td><td>0.0218</td><td>6.78</td><td>4.78</td><td>1.84</td></tr><tr><td>OREX-800032-109</td><td>2.12E-12</td><td>7.48E-14</td><td>8.68</td><td>0.05</td><td>0.1793</td><td>0.0019</td><td>0.12</td><td>10.42</td><td>0.0249</td><td>7.80</td><td>8.38</td><td>3.22</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>EWM</td><td></td><td>Error</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1.7</td><td></td><td>0.5</td></tr></tbody></table>

Note: CRE ages computed with a production rate of 4.0 × 10<sup>-14</sup> mol g<sup>-1</sup> Ma<sup>-1</sup>. α, β parameters and cosmogenic Ne ratios are given in the Supporting Information file. Suffixes o and tr refer to observed and trapped, respectively. T<sub>21</sub> is the CRE age computed with cosmogenic <sup>21</sup>Ne<sub>c</sub>. EWM, error-weighted mean (MSWD = 1.5).
<figure><img src="image_8.png" /><figcaption>FIGURE 7. Nitrogen abundances (gray bars, left Y axis) and isotopic compositions (blue diamonds, right Y axis) of four Bennu particles as a function of laser power. Abundances are given as parts per million (ppm weight).</figcaption></figure>

(2–7 Ma) proposed by Keller et al. (2025) from ¹⁰Be, ²¹Ne, ²⁶Al, ³⁶Cl cosmogenic isotope systems. High CRE ages could be a result of the irradiation of the original parent body for samples that were originally not completely shielded from GCR irradiation, and the overall dispersion of ages could represent surface gardening on Bennu due to impacts. In such a case, the youngest CRE ages could represent the epoch when Bennu was isolated from its parent body. The error-weighted mean CRE of 1.7 ± 0.5 Ma (1σ, MSWD = 1.5; Table 2) is in agreement with estimations of how long Bennu has been dynamically decoupled from the asteroid belt (1.75 ± 0.75 million years; Ballouz et al., 2020) and with small crater retention ages of 1.6–2.2 Ma (Bierhaus et al., 2022). Similarly, the CRE ages of Ryugu particles of ~5 Ma are also consistent with crater ages inferred from the crater density distribution (Cho et al., 2021).

## Nitrogen

Figure 7 shows the N abundance and isotope results of four aggregate particles analyzed together with Ne and Ar using the Nu Noblesse-HR™ noble gas mass spectrometer (Gamblin et al., 2024). As for all noble gases, stepwise heating of the samples was achieved by gradually increasing the CO₂ laser power to separate the different N components, without knowledge of the exact heating temperature. The summed N abundances (0.13–0.18 wt%) are comparable to those of CIs and generally higher than

those in Ryugu samples (Figure 8). They are, however, significantly lower than those determined by Glavin et al. (2025) for Bennu aggregates (0.23–0.25 wt%). Two of the four Bennu particles (OREX-803033-0 and OREX-803035-0) have nitrogen isotope compositions comparable to those of CI chondrites (average δ¹⁵N = 44.0 ± 0.9‰; see compilation in Broadley et al., 2023). However, the other two particles show drastic departures from CI chondrites, with enrichment (OREX-803032-0, δ¹⁵N = 78.9 ± 2.0‰) and depletion (OREX-803034-0, δ¹⁵N = 13.7 ± 2.0‰) in ¹⁵N. Given the high N content of all the samples, the low CRE age, and the absence of marked ¹⁵N enrichments in three of the four samples, the ¹⁵N-rich component is unlikely to result from contributions of cosmogenic N. In ordinary chondrites, the production rate of cosmogenic ¹⁵N (¹⁵N_c) has been estimated at 3.3 × 10⁻¹³ mol g⁻¹ Ma⁻¹ (Hashizume & Sugiura, 1995). Because ¹⁵N_c is mainly produced from oxygen, we apply this production rate to Bennu material and, for a CRE age of 3 Ma, the total amount of ¹⁵N_c should be ~1 × 10⁻¹² mol g⁻¹, negligible compared to a typical ¹⁵N content of ~4 × 10⁻⁷ mol g⁻¹ (computed for OREX-803033-0, mass = 0.0345 mg, 1534 ppm N and δ¹⁵N = 44‰). Ryugu samples also show a distribution of δ¹⁵N which is shifted toward lower δ¹⁵N values (Figure 8). This distribution has been interpreted as reflecting mixing between a ¹⁵N-rich component, in this case with a δ¹⁵N ratio similar to CIs, and a ¹⁵N-poor component with δ¹⁵N close to 0‰ (Okazaki et al., 2023).
<figure><img src="image_9.png" /></figure>

FIGURE 8. δ¹⁵N as a function of the inverse N concentration. Bennu data (this work, blue diamonds) are consistent with mixing between a low δ¹⁵N (≤20‰), N-poor (<1300 ppm) endmember and a ¹⁵N-rich (≥80‰), N-richer (<1700 ppm) component. Previously published nitrogen data (dark gray diamonds; Lauretta et al., 2024; Barnes et al., 2025) follow a similar trend. The ¹⁵N-rich component is neither apparent in CI and CM chondrites nor in Ryugu samples. For Ryugu samples, a two-component mixing has also been proposed, involving a CI-like component and a low δ¹⁵N endmember with an isotopic composition comparable to that of atmospheric N (Okazaki et al., 2023). Ryugu data are from Naraoka et al. (2023), Okazaki et al. (2023), Broadley et al. (2023), Hashizume et al. (2024). CI and CM averages are from compilation in Broadley et al. (2023).

We propose that the range of δ¹⁵N values measured in the Bennu samples (Figure 8) results from mixing of at least two nitrogen components, one rich in ¹⁵N with δ¹⁵N > 80‰ (up to 160‰ as observed in the highest temperature steps of sample OREX-803032-0), and the other one poor in ¹⁵N, with δ¹⁵N down to ~0 ‰ as seen in intermediate steps of OREX-803034-0. Mixing between at least two nitrogen components is also apparent in the step-release data within each individual sample (Figure 7) and the distribution of N isotope ratios as a function of temperature suggests that the ¹⁵N-rich component is more tightly bound than the ¹⁵N-poor component. Previously published N data for Bennu samples (Barnes et al., 2025; Lauretta et al., 2024) are broadly consistent with this trend (Figure 8).

The occurrence of the ¹⁵N-rich component is unlikely to result from the contribution of presolar material. The ³⁸Ar/³⁶Ar ratios of the present samples are similar to the Q value within error. In particular, data from the last four heating steps of sample OREX-803032-0, which show δ¹⁵N values higher than +140‰, have a ³⁸Ar/³⁶Ar weighted mean of 0.1904 ± 0.0015 (Supporting Information S1). If, in addition to Q, there was a contribution of a presolar component, such a value would select P3 (0.19011 ± 0.0010) as a possible presolar component. The occurrence of P3 would be consistent with the generally

low ²⁰Ne/²²Ne ratios of this sample (7.8–9.6; Supporting Information S2), which also characterizes P3 Ne. However, P3 is hosted by nanodiamonds, which have strong depletions in ¹⁵N (δ¹⁵N = -360 ‰, e.g., Russell et al., 1996) that do not match the observed N isotope composition of these steps. Moreover, the presolar phases that are rich in ¹⁵N (SiC, Si₃N₄, graphite) have Ne and Ar isotope compositions that are inconsistent with those observed in this study.

Nitrogen in carbonaceous chondrites is mainly hosted by soluble and insoluble organic matter. Given the Q-like signature of Xe, Kr, and Ar in Bennu (and Ryugu) material, we propose that N similarly originates from organic phase(s), whose N isotopic compositions may vary depending on their origin(s). Because there may be a gradient of ¹⁵N enrichments as a function of heliocentric distance (Füri & Marty, 2015; and references therein), Bennu material might have formed from a *mélange* of organics of various origins, possibly synthesized in different regions of the nascent solar system. Indeed, the presence of organic matter having different N isotopic compositions and origins was also observed in bulk and in situ studies of Bennu samples (Barnes et al., 2025; Glavin et al., 2025). The fact that bulk ¹⁵N enrichments of 80‰ are rarely seen in carbonaceous chondrites may indicate that the OSIRIS-REx spacecraft sampled primitive matter that has been better preserved than in meteorites or that originated from larger heliocentric distances than in most carbonaceous chondrites.

The ²²Ne/N versus ³⁶Ar/N diagram (Figure 9) illustrates the fact that Bennu and Ryugu samples have greater noble gas to N ratios compared to most carbonaceous chondrites, particularly CIs and Renazzo-type (CR) chondrites. For Ryugu samples, the noble gas/N ratios being higher than for CIs has been interpreted as reflecting their lower N content together with high noble gas contents compared to CIs (Broadley et al., 2023). However, this explanation does not hold for Bennu samples, which have N contents comparable to those of CIs (Figure 8) and twice as much noble gas as these meteorites (Figure 2). Hence, the greater noble gas/N ratios of the Bennu data in Figure 9 suggest a higher Q noble gas content rather than a relative loss of N. Presolar noble gases hosted by nanodiamonds are relatively resistant to aqueous alteration and are mainly affected by thermal metamorphism (Huss & Lewis, 1994), which is unlikely to have been significant in Bennu and Ryugu materials (as discussed in “Noble Gas Abundances” section). The higher ²²Ne/N ratio of Bennu samples compared to CI and Ryugu samples therefore suggests that Bennu material may be richer in nanodiamonds. This possibility may ultimately be tested by the extraction and quantification of nanodiamonds from these materials.
<figure><img src="image_10.png" /></figure>

FIGURE 9. Three-element plots of noble gases and nitrogen in Bennu, Ryugu, and carbonaceous chondrites (after Broadley et al., 2023). “Atm” stands for the terrestrial atmosphere (data from Ozima & Podosek, 2002), “BM” stands for bulk terrestrial mantle (Marty & Genda, 2024), “BSE” represents Bulk Silicate Earth (including atmosphere, mantle, and crust; Marty & Genda, 2024), and “ND” stands for nanodiamonds (Huss & Lewis, 1994; Russell et al., 1996). Q data are from after Broadley et al. (2023); Ryugu, CI, and CM data are from Mazor et al. (1970), Nagao et al. (1984), Bekaert et al. (2019), King et al. (2019), Krietsch (2020), Krietsch et al. (2021), Okazaki et al. (2023), Broadley et al. (2023), Gamblin et al. (2024), and references therein. “Heated CI” refers to results from heating experiments of CI material (Füri et al., 2013).

## ASTEROID-EARTH RELATIONSHIP

A high noble gas content of primitive material has potential implications for the budget of volatile delivery to Earth. According to some models, a limited supply of carbonaceous chondritic (CC) material might have been sufficient to provide the inventory of H, C, N, and noble gases to the silicate Earth (mantle and surface reservoirs, excluding the core) (Albarède et al., 2013; Alexander et al., 2012; Marty, 2012). A detailed mass balance, taking into account the terrestrial budget of these elements, suggests that a minimum of 2% carbonaceous chondrite (CC)-like material could account for the oceans, atmosphere, and mantle volatiles (Marty, 2012). This fraction is larger than the contribution of chondritic material required to supply platinum group elements (PGE) to the mantle (~0.5%; Righter, 2003), presumably as a late veneer after the last episode of mantle-core equilibration. This discrepancy between volatiles and PGE budgets was taken as evidence for the supply of terrestrial volatiles during the main stages of terrestrial accretion and not only as a late veneer (Dauphas & Morbidelli, 2014; Marty, 2012). Because Bennu and Ryugu are richer in noble gases than CCs by a factor of two or more, the contribution of Bennu/Ryugu-like material required to match the terrestrial inventory of

noble gases could be ≤1%, thus reducing the discrepancy with the budget of PGEs. This proportion is still marginally higher than the amount of late accretion from the PGE perspective, but, given uncertainties in inventories as well as in accretionary processes, this suggests that a late veneer of Bennu/Ryugu-like material could have supplied a significant if not major, share of volatile elements to the Earth's surface.

From the perspective of volatile elements (noble gases and stable isotopes of H and N), the composition of the terrestrial atmosphere points to a heritage of carbonaceous chondrite-like material (Alexander et al., 2012; Marty, 2012), whereas mantle volatiles are consistent with the contribution of solar gas (Honda et al., 1991; Péron et al., 2016; Williams & Mukhopadhyay, 2019; Yokochi & Marty, 2004) mixed with non-carbonaceous material (Piani et al., 2020). We tested this possibility with Bennu and Ryugu Ne-Ar compositions (Figure 10). The mean values of Bennu and Ryugu data are close to those of CIs but slightly offset to the right of Earth's atmosphere, possibly due to the addition of mantle gases rich in solar Ne to the latter. The isotopic fractionation of an initially solar-like atmosphere during escape (Pepin, 1991) cannot account for the position of the present samples in Figure 10, and the observed composition is more consistent with a contribution of CC-like material. Overall, asteroid and CI chondrite data confirm the potential delivery of a significant fraction of atmospheric noble gases by CI/Bennu/Ryugu-like material. CM-like material could also fit, although it would require more accreted mass than material from Bennu/Ryugu, challenging the PGE delivery problem. In this scenario, Ne isotope ratios and Ar/Ne ratios suggest that a major fraction (90%) of atmospheric neon originated from nanodiamonds, which makes sense for an element with such a nobility.

## CONCLUSION

The noble gas and nitrogen content and isotopic composition of Bennu (and Ryugu) samples present similarities with CI chondrites but also significant differences:

* Bennu (and Ryugu) samples display noble gas contents higher by a factor of ~2 than CIs, even if their main components (Q, presolar) are similar. Such a high noble gas content will require re-evaluating the potential contribution of volatile-rich material during terrestrial accretion.

* The cosmic ray exposure ages of Bennu samples are within 1–3 Ma, consistent with the estimated age of Bennu’s near-Earth lifetime yet lower than CRE ages for Ryugu (4–5 Ma).
<figure><img src="image_11.png" /></figure>

FIGURE 10. $^{20}$Ne/$^{22}$Ne vs. $^{36}$Ar/$^{22}$Ne ratios (after Marty, 2012). In this format, two-component mixing trends appear as straight lines linking the endmembers. The diagram compares the compositions of Bennu, Ryugu, CI, and CM data with those of the terrestrial atmosphere (“Atm.”; Ozima & Podosek, 2002) and the bulk mantle (“BM”; Marty & Genda, 2024). Thick symbols represent the means, with error bars corresponding to 1σ for each data set. HL, P3, Q, solar, and SW data are from Ott (2014). HL and P3 components are hosted by nanodiamonds (“ND”; Huss & Lewis, 1994; Ott, 2014). The green dotted lines represent mixing curves between HL and P3, on one hand, and between HL and Q, on another hand. The “90%” markers indicate the fraction of neon originating from nanodiamonds. The curve on the left-hand side displays the evolution of a solar-like atmosphere undergoing mass-dependent elemental ($^{36}$Ar/$^{22}$Ne) and isotope ($^{20}$Ne/$^{22}$Ne) fractionation. Non-carbonaceous meteorite data would plot on the right-hand side and cannot account for the composition of Earth’s atmosphere (Marty, 2022).

* Bennu appears to have a N component rich in $^{15}$N that was not previously seen in CIs or Ryugu. Further N analysis of Bennu material should allow investigation of the host(s) of this component.

* These characteristics attest to the better preservation of pristine asteroidal material delivered to Earth by spacecraft compared with carbonaceous chondrites having interacted with the terrestrial environment.

* Bennu data confirm a potential link between carbonaceous material and the terrestrial atmosphere. Interestingly, atmospheric neon might have originated in large part from extraterrestrial nanodiamonds.

**Acknowledgments**—This material is based upon work supported by NASA under Contract NNM10AA11C issued through the New Frontiers Program. We acknowledge the entire OSIRIS-REx team for enabling the return and analysis of samples from Bennu. This

work was made possible by the careful work of the Curation staff at NASA’s Johnson Space Center. This study was primarily funded by the European Union (ERC: IRONIS, 101087562, PHOTONIS, 695618). Views and opinions expressed are, however, those of the authors only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. Support from the Centre National d’Études Spatiales (CNES) is gratefully acknowledged. We thank Sarah Russell for handling the samples, and Bouchaib Tibari and Allan Bauer for their assistance with the noble gas mass spectrometry analyses at CRPG. Cat Wolner carefully corrected several versions of this work. We are grateful to an anonymous reviewer and to Dr. Ingo Leya for their thorough reviews of this manuscript and their constructive comments, and to Toni Schulz for efficient editing. This work is part of a special issue to honor our friend and colleague Christian Koeberl.

**Conflict of Interest Statement**—The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

**Data Availability Statement**—All noble gas (He, Ne, Ar, Kr, Xe) data (Marty, 2025) is available at: https://doi.org/10.5281/zenodo.16779285. Ne, Ar and N data (Füri, 2025) are available at: https://doi.org/10.5281/zenodo.15472400. Instrument data products supporting the findings of this work are available via AstroMat (astromat.org) at the DOIs indicated in Tables S2 and S3.

**Editorial Handling**—Tony Schulz

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## SUPPORTING INFORMATION

Additional supporting information may be found in the online version of this article.

**S1.** Methods and all noble gas data obtained using the Thermo Scientific MC+™ mass spectrometer.

**Table S1.** Settings of the Thermo Scientific Helix MC+™ mass spectrometer used for the analysis of all noble gases.

**Table S2.** Raw processed data can be downloaded using the following DOIs.

**S2.** Methods and Ne, Ar, and N data obtained for analysis using the Nu Instruments Noblesse-HR™ mass spectrometer.

**Table S3.** Raw and processed Ne, Ar and N data can be downloaded using the following DOIs.

**S3.** Xenon three isotope diagram ($^{134}$Xe/$^{132}$Xe vs. $^{136}$Xe/$^{132}$Xe).

**S4.** Trapped Ne and cosmogenic $^{21}$Ne$_{c}$.

**S5.** Histogram of ($^{20}$Ne/$^{22}$Ne)tr ratios.

**S6.** He versus Ne isotope ratios for step-heating data.