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NASA NTRS1988

Noble gases released by vacuum crushing of EETA 79001 glass

An EETA 79001 glass sample was crushed in a vacuum to observe the gases released. About 15 pct of the total gas concentrations were a mixture of a small amount of SPB-type gas with larger proportions of another air-like component. Less than 5 pct of the SPB gas was released by crushing, while 36-40 pct of the EETV (indigenous) gas was crush-released. The results are consistent with a siting of the EETV component in 10-100 micron vesicles seen in the glass. It is suggested that the SPB component is either in vesicles less than 6 microns in diameter or is primarily sited elsewhere.

Wiens, R. C.↗
NASA NTRS1990

Mass fractionation of noble gases in diffusion-limited hydrodynamic hydrogen escape

The theory of mass fractionation by hydrogen is presently extended to atmospheres in which hydrogen is not the major constituent. This theoretical framework is applied to three different cases. In the first, it is shown that the fractionation of terrestrial atmospheric neon with respect to mantle neon is explainable as a consequence of diffusion-limited hydrogen escape from a steam atmosphere toward the end of the accretion process. In the second, the anomalously high Ar-38/Ar-36 ratio of Mars is shown to be due to hydrodynamic fractionation by a vigorously escaping and very pure hydrogen wind. In the last case, it is speculated that the currently high Martian D/H ratio emerged during the hydrodynamic escape phase which fractionated Ar.

Zahnle, Kevin↗
NASA NTRS1991

Composition of solar flare noble gases preserved in meteorite parent body regolith

Isotopic composition of solar-flare (SF) Ne was determined in acid-etched pyroxene mineral separates from the Kapoeta meteorite, a brecciated meteorite known to contain implanted solar gases. The results yield the SF Ne-20/Ne-22 ratio of 11.6 +/-0.2, confirming previous determinations of this SF ratio in lunar and meteoritic samples. The same SF Ne composition was also obtained by applying an ordinate intercept technique to the same data set. The ordinate intercept technique was then applied to the Ar and He data. The results are SF Ar-36/Ar-38 = 4.9 +/-0.1 and SF He-4/He-3 = 3800 +/-200. These values are significantly different from the solar-wind (SW) Ar and He values. It is estimated that the concentration of the SF component in Kapoeta pyroxenes is about 20 percent that of the SW component, orders of magnitude higher than expected from SW and SF proton flux measurements.

Rao, M. N.↗
NASA NTRS1992

Evolution of isotopic signatures in lunar-regolith nitrogen - Noble gases and nitrogen in grain-size fractions from regolith breccia 79035

Ilmenite and pyroxene grain-size separates from 79035 were analyzed for trapped N; the ilmenite was also analyzed for trapped Xe. Ilmenite N contains two or more isotopically distinct trapped components differing in release temperature and therefore plausibly in implantation energy. The isotopically light, higher-temperature (higher-energy?) component has a delta N-15 value equal to -180 percent, significantly above the minimum value observed in bulk 79035, suggesting that parts of 79035 were exposed on the lunar surface earlier than the ilmenite. Using trapped Ar-40/Ar-36 and cosmogenic Ne-21 (Benkert, 1989) a compaction age of about 1 Ga was derived for the ilmenite. This implies a considerably more recent exposure than previously thought, and suggests that the long-term change in delta N-15 of regolith N was more rapid than generally believed. Comparison of these results with those for black/orange glass from 74001/74002 (compaction age 3.7 Ga; delta N-15 in the range -36 to +18 percent (Kerridge et al., 1991) indicates that the long-term trend may have followed a complex evolutionary path. Data for 79035 pyroxenes are consistent with the ilmenite compaction age but suggest a more complex exposure history.

Kerridge, J. F.↗
NASA NTRS1993

Dispersion of the ratios of cosmogenic isotopes of noble gases in chondrites of different cosmic-ray exposure ages

The dispersion of ratios of (He-3/Ne-21)c and (Ne-22/Ne-21)c depending on the cosmic-ray exposure ages of meteorites is analyzed. The dispersion is increased as age decreases. This effect may be stipulated by presence of a more significant portion of meteorites of small preatmospheric sizes among meteorites of small radiation ages in comparison to meteorites of higher exposure age.

Alexeev, V. A.↗
NASA NTRS1993

Noble gases in LEW88516 shergottite: Evidence for exposure age pairing with ALH77005

LEW88516 contains excess amounts of radiogenic Ar-40 and Xe-129 that are slightly greater than those observed in ALH77005, but in the same relative proportion as much larger excesses observed in EET79001. Cosmogenic He-3 and Ne-21 abundances in LEW88516 are very similar to those for ALH77005 and are consistent with a common initiation of cosmic ray exposure -2.8 Myr ago for four of the five shergottites. Exposure of these four shergottites could have been under different shielding in a common meteoroid, or in several objects.

Bogard, D. D.↗
NASA NTRS1993

First investigation of noble gases in the Dengli H3,8 chondrite

The Dengli (H3,8) meteorite, which weighs 243.5 g, is a find from the Karakum desert. It is a complex microbreccia containing unusual clasts which are more typical for regolithic breccias than for H-chondrites. Based on comparisons of Xe and Kr content and isotopic composition, the Dengli does not differ significantly from other H-chondrites. Its exposure age is 7.6 Ma. That is in agreement with common data for the exposure age (6.2 + 0.2 Ma) of 350 H-chondrites. Dengli's K/Ar age (4.01 Ga) coincides with the same ages of many other H-chondrites. Thus the Dengli is not regolithic breccia, and it probably formed during accretion of its parent body.

Ivanova, M. A.↗
NASA NTRS1993

Noble gases in ancient asteroidal atmospheres

Analytical and numerical results presented here suggest that acceleration of photoions by the solar wind motional field is a significant loss process for Xe on asteroids about 200 km in radius or larger, if the Xe is thermalized by its interactions with the surface. For Ar, photoion acceleration can only become important for asteroids nearly 500 km in radius. Thus photoion acceleration, previously invoked for lunar samples, could be responsible for excess fission-produced Xe found associated with solar wind Xe in howarditic meteorites. The lack of such Xe in other types of meteorites may reflect either smaller parent bodies or later times of regolith exposure. Similarly, the failure to observe solar-wind-associated radiogenic Ar-40 in meteorites is consistent with the much smaller likelihood that Ar will be photoionized.

Swindle, Timothy D.↗
NASA NTRS2000

Noble Gases in the Monahans Chondrite and Halite: Ar-39 - Ar-40 Age, Space Exposure Age, Trapped Solar Gases, and Neutron Fluence

In the Monahans H5 chondrite, Zolensky et al. report the first occurrence of grains of halite (NaCl), which contain minor sylvite (KCl) and tiny inclusions of liquid water. Here we report Ar-39 - Ar-40 ages of Monahans light (4.53 Ga) and dark phases and of the halite (>4.33 Ga). We report the presence of trapped solar gases in the dark phase, demonstrating that it represents a prior regolith on the Monahans parent body, We also report the cosmic-ray exposure age of Monahans and the neutron fluence experienced by the regolith component. Because the halite grains are apparently located only in the regolith phase, they may have formed by early hydrous activity within the Monahans parent body regolith, or they may have been introduced from outside.

Bogard, Donald D.↗
NASA NTRS2009

Fischer-Tropsch-Type Production of Organic Materials in the Solar Nebula: Studies Using Graphite Catalysts and Measuring the Trapping of Noble Gases

The formation of abundant carbonaceous material in meteorites is a long standing problem and an important factor in the debate on the potential for the origin of life in other stellar systems. The Fischer-Tropsch-type (FTT) catalytic reduction of CO by hydrogen was once the preferred model for production of organic materials in the primitive solar nebula. We have demonstrated that many grain surfaces can catalyze both FTT and HB-type reactions, including amorphous iron and magnesium silicates, pure silica smokes as well as several minerals. Graphite is not a particularly good FTT catalyst, especially compared to iron powder or to amorphous iron silicate. However, like other silicates that we have studied, it gets better with exposure to CO. N2 and H2 over time: e.g., after formation of a macromolecular carbonaceous layer on the surfaces of the underlying gains. While amorphous iron silicates required only 1 or 2 experimental runs to achieve steady state reaction rates, graphite only achieved steady state after 6 or more experiments. We will present results showing the catalytic action of graphite grains increasing with increasing number of experiments and will also discuss the nature of the final "graphite" grains aster completion of our experiments.

Nuth, Joseph A., III↗
NASA NTRS2010

Trapping Planetary Noble Gases During the Fischer-Tropsch-Type Synthesis of Organic Materials

When hydrogen, nitrogen and CO arc exposed to amorphous iron silicate surfaces at temperatures between 500 - 900K, a carbonaceous coating forms via Fischer-Tropsch type reactions!, Under normal circumstances such a catalytic coating would impede or stop further reaction. However, we find that this coating is a better catalyst than the amorphous iron silicates that initiate these rcactions:u . The formation of a self-perpetuating catalytic coating on grain surfaces could explain the rich deposits of macromolecular carbon found in primitive meteorites and would imply that protostellar nebulae should be rich in organic materiaL Many more experiments are needed to understand this chemical system and its application to protostellar nebulae.

Nuth, Joseph A.↗
NASA NTRS2010

VAPoR - Volatile Analysis by Pyrolysis of Regolith - an Instrument for In Situ Detection of Water, Noble Gases, and Organics on the Moon

We present the Volatile Analysis by Pyrolysis of Regolith (VAPoR) instrument design and demonstrate the validity of an in situ pyrolysis mass spectrometer for evolved gas analyses of lunar and planetary regolith samples. In situ evolved gas analyses of the lunar regolith have not yet been carried out and no atmospheric or evolved gas measurements have been made at the lunar poles. VAPoR is designed to do both kinds of measurements, is currently under development at NASA's Goddard Space Flight Center, and will be able to heat powdered regolith samples or rock drill fines up to 1400 C in vacuo. To validate the instrument concept, evolved gas species released from different planetary analogs were determined as a function of temperature using a laboratory breadboard. Evolved gas measurements of an Apollo 16 regolith sample and a fragment of the carbonaceous meteorite Murchison were made by VAPoR and our results compared with existing data. The results imply that in situ evolved gas measurements of the lunar regolith at the polar regions by VAPoR will be a very powerful tool for identifying water and other volatile signatures of lunar or exogenous origin as potential resources for future human exploration.

ten Kate, I. L.↗
NASA NTRS2022

Noble Gases and Nitrogen in Samples of Asteroid Ryugu Record Its Volatile Sources and Recent Surface Evolution

The Hayabusa2 spacecraft retrieved surface and subsurface samples from the carbonaceous near-Earth asteroid (162173) Ryugu, which was expected to be enriched in volatile species. The samples were collected from two locations, one undisturbed surface and the other including material excavated by an artificial impact. Unlike meteorites, these samples have experienced minimal alteration by Earth’s atmosphere. Ryugu is thought to have formed from material ejected (by an impact) from a parent body, which had experienced aqueous alteration (reactions with liquid water) ~4.56 billion years (Gyr) ago. Ryugu’s orbit later migrated from the main asteroid belt to become a near-Earth asteroid.

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