The enigma of helium and anomalous xenon

Isotopically anomalous xenon in chondrites is closely associated with low-Z noble gases, but there is no helium (or neon) in the noble gas component with normal xenon. The correlation of elemental and isotopic heterogeneities in meteoritic noble gases places stringent limits on the origin of isotopically anomalous elements in meteorites and on the formation of the solar system.     

Trapping of noble gases in proton-irradiated silicate smokes

Abstract— We have measured Ne, Ar, Kr and Xe in Si₂O₃ “smokes” that were condensed on Al substrates, vapor-deposited with various mixtures of CH₄, NH₃, H₂O and noble gases at 10 K and subsequently irradiated with 1 MeV protons to simulate conditions during grain mantle formation in interstellar clouds. The noble gases were analyzed using conventional stepwise heating and static noble gas mass spectrometry. Neither Ne nor Ar is retained by the samples upon warming to room temperature, but Xe is very efficiently trapped and retained. Kr is somewhat less effectively retained, typically depleted by factors of about 10–20 relative to Xe. Isotopic fractionation favoring the heavy isotopes of Xe and Kr of about 5–10‰/amu is observed. Correlations between the specific chemistry of the vapor deposition and heavy noble gas retention are most likely the result of competition by the various species for irradiation-produced trapping sites. The concentration of Xe retained by some of these smokes exceeds that observed in phase Q of meteorites and, like phase Q, they do not seem to be carriers of the light noble gases. Such artificially prepared material may, therefore, offer clues concerning the incorporation of the heavy planetary noble gases in meteoritic material and the nature of phase Q.     

Noble gases in Muong Nong‐type tektites and their implications

Abstract— We have the elemental abundances and isotopic compositions of noble gases in Muong Nong‐type tektites from the Australasian strewn field by crushing and by total fusion of the samples. We found that the abundances of the heavy noble gases are significantly enriched in Muong Nong‐type tektites compared to those in normal splash‐form tektites from the same strewn field. Neon enrichments were also observed in the Muong Nong‐type tektites, but the Ne/Ar ratios were lower than those in splash‐form tektites because of the higher Ar contents in the former. The absolute concentrations of the heavy noble gases in Muong Nong‐type tektites are similar to those in impact glasses. The isotopic ratios of the noble gases in Muong Nong‐type tektites are mostly identical to those in air, except for the presence of radiogenic ⁴⁰Ar. The obtained K‐Ar ages for Muong Nong‐type tektites were about 0.7 Myr, similar to ages of other Australasian tektites. The crushing experiments suggest that the noble gases in the Muong Nong‐type tektites reside mostly in vesicles, although Xe was largely affected by adsorbed atmosphere after crushing. We used the partial pressure of the heavy noble gases in vesicles to estimate the barometric pressure in the vesicles of the Muong Nong‐type tektites. Likely, Muong Nong‐type tektites solidified at the altitude (between the surface and a maximum height of 8–30 km) lower than that for splash‐form tektites.     

Noble gas adsorption with and without mechanical stress: Not Martian signatures but fractionated air

Abstract– Sample preparation, involving physical and chemical methods, is an unavoidable step in geochemical analysis. From a noble gas perspective, the two important effects are loss of sample gas and/or incorporation of air, which are significant sources of analytical artifacts. This article reports on the effects of sample exposure to laboratory air without mechanical influence and during sample grinding. The experiments include pure adsorption on terrestrial analog materials (gibbsite and olivine) and grinding of Martian meteorites. A consistent observation is the presence of an elementally fractionated air component in the samples studied. This is a critical form of terrestrial contamination in meteorites as it often mimics the heavy noble gas signatures of known extra‐terrestrial end‐members that are the basis of important conclusions about the origin and evolution of a meteorite. Although the effects of such contamination can be minimized by avoiding elaborate sample preparation protocols, caution should be exercised in interpreting the elemental ratios (Ar/Xe, Kr/Xe), especially in the low‐temperature step extractions. The experiments can also be transferred to the investigation of Martian meteorites with long terrestrial residence times, and to Mars, where the Mars Science Laboratory mission will be able to measure noble gas signatures in the current atmosphere and in rocks and soils collected on the surface in Gale crater.     

NOBLE GAS ANOMALIES AND SYNTHESIS OF THE CHEMICAL ELEMENTS

There are two types of planetary noble gases: One, containing isotopically “anomalous” argon, krypton and xenon but isotopically “normal” helium and neon, was derived from outer stellar regions. The other, consisting almost entirely of isotopically “normal” argon, krypton and xenon, with little or no helium or neon, was derived from inner stellar regions. Mixing of nucleosynthesis products from different regions of a supernova is responsible for the observed correlations between elemental and isotopic ratios of planetary noble gases in different classes of meteorites. The solar system condensed directly from the chemically and isotopically heterogeneous debris of a single supernova. There is no convincing evidence, however, of separate nucleogenetic components in neon. Fractionation and spallation can account for all previously identified components of trapped meteoritic neon, Ne-A, Ne-B, Ne-C, Ne-D, Ne-E, Ne-Al, Ne-A2, Ne-E(L), Ne-E(H) and Ne-O, and this same mechanism also explains differences between the isotopic compositions of meteoritic, atmospheric, and solar wind neon. Variations in the abundance pattern of planetary noble gases are primarily the result of stellar fusion reactions and physical adsorption, rather than gas solubility.     

Stability of streams and lakes on Mars

Under present climatic conditions streams and lakes on Mars will freeze. Freezing is slow and would have a negligible effect in impeding flow of the large floods that are believed to have eroded the outflow channels. Valley networks are more difficult to form under current climatic conditions since they appear to have formed by slow erosion by streams of modest discharges. Freezing of small Martian streams was modeled for a variety of climatic conditions on the supposition that the Martian atmosphere may have been considerably thicker in the past when the valley networks formed. The modeling involves examination of the energy balance at the upper and lower surfaces of ice on streams to determine the rate at which the ice thickens with time. The results indicate that freezing rates are not strongly dependent on atmospheric pressure. With no wind, increasing the pressure by a factor of 10 cuts the time taken to freeze solid only by about a factor of about 2. Under windy conditions dependence on atmospheric pressure is even weaker. The distance that water could travel in a stream before flow is arrested by freezing is also calculated. The distances depend on the initial temperature of the stream and when icings develop, but in general, if a stream deeper than 2 m can be initiated and sustained, the water within it can survive long enough to cut most of the valley networks observed. The main problem with forming the valley is initiating the flow. Groundwater seepage alone appears inadequate because of the difficulty of recharging the groundwater system. Melting of ice precipitated onto the surface following injection of water into the atmosphere by large impacts is a possible source of water, but the climatic conditions under which the ice could melt and the water be collected into streams that can survive long enough to cut the valley is uncertain.     

Effects of experimental aqueous alteration on the abundances of argon‐rich noble gases in the Ningqiang carbonaceous chondrite

Abstract— Ar‐rich noble gases, the so‐called “subsolar” noble gases, are a major component of heavy primordial noble gases in unequilibrated ordinary chondrites and some classes of anhydrous carbonaceous chondrites, whereas they are almost absent in hydrous carbonaceous chondrites that suffered extensive aqueous alteration. To understand the effects of aqueous alteration on the abundance of Ar‐rich noble gases, we performed an aqueous alteration experiments on the Ningqiang type 3 carbonaceous chondrite that consists entirely of anhydrous minerals and contains Ar‐rich noble gases. Powdered samples and deionized neutral water were kept at 200 °C for 10 and 20 days, respectively. Mineralogical analyses show that, during the 10‐day alteration, serpentine and hematite formed at the expense of olivine, low‐Ca pyroxene, and sulfide. Noble gas analyses show that the 10‐day alteration of natural Ningqiang removed 79% of the primordial ³⁶Ar, 68% of the ⁸⁴Kr, and 60% of the ¹³²Xe, but only 45% of the ⁴He and 53% of the primordial ²⁰Ne. Calculated elemental ratios of the noble gases removed during the 10‐day alteration are in the range of those of Ar‐rich noble gases. These results indicate that Ar‐rich noble gases are located in materials that are very susceptible to aqueous alteration. In contrast, heavy primordial noble gases remaining in the altered samples are close to Q gas in elemental and isotope compositions. This indicates that phase Q is much more resistant to aqueous alteration than the host phases of Ar‐rich noble gases. In the 20‐day sample, the mineralogical and noble gas signatures are basically similar to those of the 10‐day sample, indicating that the loss of Ar‐rich noble gases was completed within the 10‐day alteration. Our results suggest that almost all of the Ar‐rich noble gases were lost from primitive asteroids during early, low‐temperature aqueous alteration.     

The effect of pyridine treatment on phase Q: Orgueil and Allende

Marrocchi et al. (2005) reported that low‐temperature fractions of heavy noble gases were largely removed upon pyridine treatment of the Orgueil CI meteorite. As pyridine is known to induce the swelling of the macromolecular network of organic matter, they concluded that the low‐temperature phase Q is macromolecular organic carbon. However, Busemann et al. (2008) showed that pyridine had no significant effect on the noble gas contents for other very primitive meteorites, such as CM and CR. Therefore, we prepared an HF–HCl residue and the pyridine‐treated residue of Orgueil, and re‐examined the results of Marrocchi et al. (2005) by analyzing all noble gases. We confirmed that heavy noble gases are surely removed by the pyridine treatment, but the degree of the loss of heavy noble gases is generally small, and is even smaller for the lighter noble gases. Furthermore, we could not observe the evidence of Xe isotopic ratios by removing only phase Q after the pyridine treatment. We further prepared the HF–HCl residue and the pyridine‐treated residue of the Allende CV3 meteorite and performed noble gas analyses. For Allende, there is no significant change in the elemental abundances after the pyridine treatment. These results suggest that only Orgueil is special, and it is likely that the gas loss of the Orgueil residue is due to the loss of some kind of organic matter that was formed and that adsorbed the fractionated Q and HL gases during the aqueous alteration within the parent body of Orgueil.     

SOLAR ABUNDANCES OF THE ELEMENTS

The isotopic compositions of noble gases in the solar wind show high enrichments of light isotopes. When corrected for mass fractionation all five noble gases there can be resolved in terms of the two primitive noble gas components that have been identified in planetary solids. Reasons are presented for assigning the fractionation to a solar process that selectively enriches lighter nuclei at the surface of the Sun. When abundances of the elements at the Sun's surface are corrected for this fractionation, it is shown that atomic abundances for major elements in the bulk Sun are (in decreasing order): Fe, Ni, O, Si, S and Mg. Solar elements at about the 1% atomic abundance level include He, C, Ne, Ca and Cr. These results suggest that fusion of hydrogen is probably not the Sun's primary energy source.     

Acid‐susceptive material as a host phase of argon‐rich noble gas in the carbonaceous chondrite Ningqiang

Abstract— A fine‐grained dark inclusion in the Ningqiang carbonaceous chondrite consists of relatively pristine solar nebular materials and has high concentrations of heavy primordial rare gases. Trapped 36Ar concentration amounts to 6 times 10^?6 cc STP/g, which is higher than that of Ningqiang host by a factor of three. Light HF‐HCl etching of the dark inclusion removed 86, 73, and 64% of the primordial ³⁶Ar, ⁸⁴Kr, and ¹³²Xe, respectively. Thus, the majority of the noble gases in this inclusion are located in very acid‐susceptive material. Based on the elemental composition, the noble gases lost from the dark inclusion during the acid‐treatments are Ar‐rich, and the noble gases remaining in the inclusion are Q and HL gases. Transmission electron microscopy showed that the acid treatments removed thin Si, Mg, and Fe‐rich amorphous rims present around small olivine and pyroxene grains in the dark inclusion, suggesting that the Ar‐rich gases reside in the amorphous layers. A possible origin of the Ar‐rich gases is the acquisition of noble‐gas ions with a composition fractionated relative to solar abundance favoring the heavy elements by the effect of incomplete ionization under plasma conditions at 8000 K electron temperature.     

Anomalous Ne enrichments in tektites

Abstract— We measured noble gases and Ne isotopic compositions of five tektites collected from three different strewn fields. The elemental abundance patterns of noble gases in all samples show anomalous Ne enrichments relative to air. Ne isotopic compositions in tektites are in good agreement with that of atmospheric Ne, suggesting that Ne has diffused in from the atmosphere. It is conceivable that the high relative Ne abundance is essentially an equilibrium effect, i.e., storage of Ne in vesicles rather than the glass itself, facilitated by the relatively high diffusion coefficient of Ne.     

Interstellar Grains in Primitive Meteorites: Diamond,Silicon Carbide,and Graphite

Abstract— Primitive meteorites contain a few parts per million (ppm) of pristine interstellar grains that provide information on nuclear and chemical processes in stars. Their interstellar origin is proven by highly anomalous isotopic ratios, varying more than 1000-fold for elements such as C and N. Most grains isolated thus far are stable only under highly reducing conditions (C/O > 1), and apparently are “stardust” formed in stellar atmospheres. Microdiamonds, of median size ～ 10 Å, are most abundant (～ 400–1800 ppm) but least understood. They contain anomalous noble gases including Xe-HL, which shows the signature of the r- and p-processes and thus apparently is derived from supernovae. Silicon carbide, of grain size 0.2–10 μm and abundance ～ 6 ppm, shows the signature of the s-process and apparently comes mainly from red giant carbon (AGB) stars of 1–3 solar masses. Some grains appear to be ≥10⁹ a older than the Solar System. Graphite spherules, of grain size 0.8–7 μm and abundance <2 ppm, contain highly anomalous C and noble gases, as well as large amounts of fossil ²⁶Mg from the decay of extinct ²⁶Al. They seem to come from at least three sources, probably AGB stars, novae, and Wolf-Rayet stars.     

A theoretical investigation into the trapping of noble gases by clathrates on Titan

In this paper, we use a statistical thermodynamic approach to quantify the efficiency with which clathrates on the surface of Titan trap noble gases. We consider different values of the Ar, Kr, Xe, CH₄, C₂H₆ and N₂ abundances in the gas phase that may be representative of Titan's early atmosphere. We discuss the effect of the various parameters that are chosen to represent the interactions between the guest species and the ice cage in our calculations. We also discuss the results of varying the size of the clathrate cages. We show that the trapping efficiency of clathrates is high enough to significantly decrease the atmospheric concentrations of Xe and, to a lesser extent, of Kr, irrespective of the initial gas phase composition, provided that these clathrates are abundant enough on the surface of Titan. In contrast, we find that Ar is poorly trapped in clathrates and, as a consequence, that the atmospheric abundance of argon should remain almost constant. We conclude that the mechanism of trapping noble gases via clathration can explain the deficiency in primordial Xe and Kr observed in Titan's atmosphere by Huygens, but that this mechanism is not sufficient to explain the deficiency in Ar.     

The irradiation history of the Ghubara (L5) regolith breccia

Abstract— We measured cosmic‐ray products—noble gases, radionuclides, thermoluminescence, and nuclear tracks—and trace element contents and mineralogy of samples of three orthogonal and mutually intersecting cores (41–46 cm long) of a 101.6 kg Ghubara individual (1958,805) at The Natural History Museum, London. The xenoliths, like the host, have high concentrations of trapped solar gases and are heavily shocked. While contents of noble gases and degree of shock‐loading in this individual and three others differ somewhat, the data indicate that Ghubara is a two‐generation regolith breccia. Contents of cosmogenic ²⁶Al and ¹⁰Be and low track densities indicate that the Ghubara individuals were located more than 15 cm below the surface of an 85 cm meteoroid. Because of its large size, Ghubara's cosmic‐ray exposure age is poorly defined to be 15–20 Ma from cosmogenic nuclides. Ghubara's terrestrial age, based on ¹⁴C data, is 2–3 ka. Not only is Ghubara the first known case of a two‐generation regolith breccia on the macroscale, it also has a complicated thermal and irradiation history.     

Production of noble gases near the surface of Europa and the prospects for in situ chronology

The age of the surface of Europa is probably tens of Myr or less, but is poorly constrained. Two different geochronology schemes could potentially be applied to near-surface samples to provide far more precise ages. First, the surface salts apparently contain enough potassium to make potassium-argon dating feasible. Second, the bombardment of the surface with both galactic cosmic rays and protons trapped within the jovian magnetosphere will cause nuclear reactions that can lead to measurable buildups of cosmogenic noble gases, which can be used to determine both cosmic-ray exposure ages and erosion, deposition, or mixing rates for surface modification. The major differences between Europa's salt-rich ice and the rocks (meteorites, lunar samples and terrestrial rocks) in which cosmogenic noble gases are normally measured are that the abundance of target elements for nuclear reactions creating neon and argon are lower (because of the high water content), but neutron-capture reactions, particularly ³⁵Cl(n,γ)³⁶Cl(β⁻)³⁶Ar, are enhanced because of the thermalizing effects of the water. As well as presenting calculations of noble gas production near the surface of Europa, we also show that the measurements required to determine ages are within reach of technology in the near future, if an instrument can be landed on the surface of Europa.     

Noble gas record,collisional history,and pairing of CV,CO, CK,and other carbonaceous chondrites

Abstract— Concentration and isotopic composition of the light noble gases as well as of ⁸⁴Kr, ¹²⁹Xe, and ¹³²Xe have been measured in bulk samples of 60 carbonaceous chondrites; 45 were measured for the first time. Solar noble gases were found in nine specimens (Arch, Acfer 094, Dar al Gani 056, Graves Nunataks 95229, Grosnaja, Isna, Mt. Prestrud 95404, Yamato (Y) 86009, and Y 86751). These meteorites are thus regolith breccias. The CV and CO chondrites contain abundant planetary‐type noble gases, but not CK chondrites. Characteristic features of CK chondrites are high ¹²⁹Xe/¹³²Xe ratios. The petrologic type of carbonaceous chondrites is correlated with the concentration of trapped heavy noble gases, similar to observations shown for ordinary chondrites. However, this correlation is disturbed for several meteorites due to a contribution of atmospheric noble gases, an effect correlated to terrestrial weathering effects. Cosmic‐ray exposure ages are calculated from cosmogenic ²¹Ne. They range from about 1 to 63.5 Ma for CO, CV, and CK classes, which is longer than exposure ages reported for CM and CI chondrites. Only the CO3 chondrite Isna has an exceptionally low exposure age of 0.15 Ma. No dominant clusters are observed in the cosmic‐ray exposure age distribution; only for CV and CK chondrites do potential peaks seem to develop at ～9 and ～29 Ma. Several pairings among the chondrites from hot deserts are suggested, but 52 of the 60 investigated meteorites are individual falls. In general, we confirm the results of Mazor et al. (1970) regarding cosmic‐ray exposure and trapped heavy noble gases. With this study, a considerable number of new carbonaceous chondrites were added to the noble gas data base, but this is still not sufficient to obtain a clear picture of the collisional history of the carbonaceous chondrite groups. Obviously, the exposure histories of CI and CM chondrites differ from those of CV, CO, and CK chondrites that have much longer exposure ages. The close relationship among the latter three is also evident from the similar cosmic‐ray exposure age patterns that do not reveal a clear picture of major breakup events. The CK chondrites, however, with their wide range of petrologic types, form the only carbonaceous chondrite group which so far lacks a solar‐gas‐bearing regolith breccia. The CK chondrites contain only minute amounts of trapped noble gases and their noble gas fingerprint is thus distinguishable from the other groups. In the future, more analyses of newly collected CK chondrites are needed to unravel the genetic and historic evolution of this group. It is also evident that the problems of weathering and pairing have to be considered when noble gas data of carbonaceous chondrite are interpreted.     

Noble gas study of a philippinite with an unusually large bubble

Abstract— A philippinite with a large bubble (volume ?5 cm³) was crushed in a specifically constructed device under vacuum. The total pressure, the major gas components, and the concentration and the isotopic composition of noble gases in the trapped gas were measured. The total gas pressure was found to be low, ～10^?4 atm. Compared to terrestrial atmosphere, the abundances of He and Ne are considerably more enriched than the concentrations of the heavy noble gases. Unusually high ²⁰Ne/²²Ne and ²¹Ne/²²Ne ratios were measured in the bubble gas. These ratios are higher than values expected for any steady state process and are interpreted to reflect very fast nonsteady state diffusion in the early stages of tektite formation.     

Charge States of Krypton and Xenon in the Solar Wind

We calculate charge state distributions of Kr and Xe in a model for two different types of solar wind using the effective ionization and recombination rates provided from the OPEN_ADAS data base. The charge states of heavy elements in the solar wind are essential for estimating the efficiency of Coulomb drag in the inner corona. We find that xenon ions experience particularly low Coulomb drag from protons in the inner corona, comparable to the notoriously weak drag of protons on helium ions. It has been found long ago that helium in the solar wind can be strongly depleted near interplanetary current sheets, whereas coronal mass ejecta are sometimes strongly enriched in helium. We argue that if the extraordinary variability of the helium abundance in the solar wind is due to inefficient Coulomb drag, the xenon abundance must vary strongly. In fact, a secular decrease of the solar wind xenon abundance relative to the other heavier noble gases (Ne, Ar, Kr) has been postulated based on a comparison of noble gases in recently irradiated and ancient samples of ilmenite in the lunar regolith. We conclude that decreasing solar activity and decreasing frequency of coronal mass ejections over the solar lifetime might be responsible for a secularly decreasing abundance of xenon in the solar wind.     

An interdisciplinary study of weathering effects in ordinary chondrites from the Acfer region,Algeria

Abstract— Weathering effects on meteorite finds from the Acfer region were studied by various analytical techniques and in dependence on the depth of sampling. In thin sections of weathered meteorites, weathering effects usually decrease from the outside to the interior of the meteorite. The results of evolved gas analysis indicate that variation in weathering between surface and core is not significant in respect to the formation of Fe-oxyhydroxides. The secondary alteration effects in the noble gases are distributed unevenly throughout the specimens, as seen in the nonsystematic differences observed for the heavy noble gases. Chemical analyses show significant enrichment of Ba and Sr in the outer parts of the weathered samples due to element contamination through aqueous solution. Iron, Ni, and Co are partly flushed from the system as the metal oxidation proceeds. Oxygen isotopes show increases in δ¹⁸O and δ¹⁷O with increasing terrestrial age. For a set of H3 chondrites, the degree of weathering determined from the water content was correlated with terrestrial ages and is discussed with respect to possible weathering mechanisms.     

Noble gases in planetary atmospheres: Implications for the origin and evolution of atmospheres

The radiogenic and primordial noble gas content of the atmospheres of Venus, Earth, and Mars are compared with one another and with the noble gas content of other extraterrestial samples, especially meteorites. The fourfold depletion of ⁴⁰Ar for Venus relative to the Earth is attributed to the outgassing rates and associated tectonics and volcanic styles for the two planets diverging significantly within the first billion or so years of their history, with the outgassing rate for Venus becoming much less than that for the Earth at subsequent times. This early divergence in the tectonic style of the two planets may be due to a corresponding early onset of the runaway greenhouse on Venus. The 16-fold depletion of ⁴⁰Ar for Mars relative to the Earth may be due to a combination of a mild K depletion for Mars, a smaller fraction of its interior being outgassed, and to an early reduction in its outgassing rate. Venus has lost virtually all of its primordial He and some of its radiogenic He. The escape flux of He may have been quite substantial in Venus' early history, but much diminished at later times, with this time variation being perhaps strongly influenced by massive losses of H₂ resulting from efficient H₂O loss processes.Key trends in the primordial noble gas content of terrestial planetary atmospheres include (1) a several orders of magnitude decrease in ²⁰Ne and ³⁶Ar from Venus to Earth to Mars; (2) a nearly constant ²⁰Ne/³⁶Ar ratio which is comparable to that found in the more primitive carbonaceous chondrites and which is two orders of magnitude smaller than the solar ratio; (3) a sizable fractionation of Ar, Kr, and Xe from their solar ratios, although the degree of fractionation, especially for ³⁶Ar/¹³²Xe, seems to decrease systematically from carbonaceous chondrites to Mars to Earth to Venus; and (4) large differences in Ne and Xe isotopic ratios among Earth, meteorites, and the Sun. Explaining trends (2), (2) and (4), and (1) pose the biggest problems for the solar-wind implantation, primitive atmosphere, and late veneer hypotheses, respectively. It is suggested that the grain-accretion hypothesis can explain all four trends, although the assumptions needed to achieve this agreement are far from proven. In particular, trends (1), (2), (3), and (4) are attributed to large pressure but small temperature differences in various regions of the inner solar system at the times of noble gas incorporation by host phases; similar proportions of the host phases that incorporated most of the He and Ne on the one hand (X) and Ar, Kr, and Xe on the other hand (Q); a decrease in the degree of fractionation with increasing noble-gas partial pressure; and the presence of interstellar carriers containing isotopically anomalous noble gases.Our analysis also suggests that primordial noble gases were incorporated throughout the interior of the outer terrestial planets, i.e., homogeneous accretion is favored over inhomogeneous accretion. In accord with meteorite data, we propose that carbonaceous materials were key hosts for the primordial noble gases incorporated into planets and that they provided a major source of the planets' CO₂ and N₂.