F. Bühler

Solar Wind Neon from Genesis: Implications for the Lunar Noble Gas Record

Lunar soils have been thought to contain two solar noble gas components with distinct isotopic composition. One has been identified as implanted solar wind, the other as higher-energy solar particles. The latter was puzzling because its relative amounts were much too large compared with present-day fluxes, suggesting periodic, very high solar activity in the past. Here we show that the depth-dependent isotopic composition of neon in a metallic glass exposed on NASAs Genesis mission agrees with the expected depth profile for solar wind neon with uniform isotopic composition. Our results strongly indicate that no extra high-energy component is required and that the solar neon isotope composition of lunar samples can be explained as implantation-fractionated solar wind.

Apollo 11 Solar Wind Composition Experiment: First Results

The helium-4 solar wind flux during the Apollo 11 lunar surface excursion was (6.3 � 1.2) x 106 atoms per square centimeter per second. The solar wind direction and energy are essentially not perturbed by the moon. Evidence for a lunar solar wind albedo was found.

Trapping of the solar wind in solids: Part I. Trapping probability of low energy He, Ne and Ar ions

Abstract The trapping probability in Al foils of He, Ne and Ar ions with energies between 0.46 and 7 keV has been determined. Argon is trapped quantitatively for ion energies higher than 2.5 keV. At 2.5 keV the trapping probabilities of neon and helium are about 0.6. For lower energies the trapping probability of argon decreases rapidly. No saturation effects were observed for integrated bombardment fluxes up to 2 × 10 14 Ar ions/cm 2 at 2.5 keV and 3 × 10 13 Ar ions/cm 2 at 0.46 keV. The trapped gases are held quite firmly. Foils bombarded with ions of 2.5 and 7.5 keV were heated at 200 and 400°C for times up to 650 hours. Only 10–20% of the helium and virtually no neon and argon were lost at 200°C. However, at 400°C, gas losses become quite serious within 24 hours. These results show that an Al foil exposed to the solar wind would trap and retain a large fraction of the solar wind ions.

Fingerprints of carbon, nitrogen, and silicon isotopes in small interstellar SiC grains from the murchison meteorite

We report ion microprobe determinations of the carbon, nitrogen, and silicon isotopic compositions of small SiC grains (0.2–2.4 μm) from the Murchison CM2 chondrite. Analyses were made on samples containing variable numbers of grains (of sizes 0.2–1 μm) and on fourteen individual grains (1.3–2.4 μm). In some cases the multiple-grain sample compositions were probably dominated by only one or two grains. Total ranges observed are: 2.9 2 μm) SiC grains. Two rare components appear .to be present in the smaller-size fraction (0.2–1 μm), one characterized by 12C13C ~ 12−16 and the other (not directly observed) by very heavy nitrogen (14N15N < 100). The carbon and nitrogen isotopic compositions qualitatively may reflect hydrostatic H-burning via the CNO cycle and He-burning in red giants (most grains), as well as explosive H-burning in novae. The silicon isotopic compositions of most grains qualitatively show what is the signature of He-burning (enrichment in 29Si and 30Si). The silicon isotopic composition of one grain, however, suggests a different process.

Osmium isotopes in the aerosols of the mantle volcano Mauna Loa

Aerosols and reactive gases from the spring 1984 eruption of Mauna Loa Volcano on Hawaii were collected and analyzed for osmium and its isotopic composition. The measured187Os/186Os ratio of1.14 ± 0.03 is close to the ratio in matter with solar systemRe/Os abundance. This result shows that the aerosols from Mauna Loa originated in the mantle and that their composition was not or only slightly influenced by their contact with the crust.

Trapped solar wind helium and neon in Surveyor 3 material

The He-4 and Ne-20 contents in sections of the Surveyor 3 support strut samples were determined by optical and scanning electron microscopy and are compared to the results of the Apollo solar wind composition (SWC) experiments. The He-4/Ne-20 ratio in the samples from the sunlit side of the strut was approximately 300; the ratios determined in Apollo 12 lunar fines and SWC foil were below 100. The He-4/He-3 ratios were also determined, and the ratio obtained from Surveyor 3 material is higher than those found with Apollo 11 and 12 SWC experiments. The effects of spallation by cosmic rays or solar protons, stripping by cosmic ray or energetic solar alpha particles, recycling of solar wind He and radiogenic Ne, He from terrestrial atmosphere, mass discrimination near the moon, mass dependence of trapping probability, diffusion, and contamination by lunar dust are considered.

Measurement of 3He/4He in the Local Interstellar Medium: the Collisa Experiment on Mir

An accurate measurement of the noble gas isotopic composition in the local interstellar medium (LISM) provides a constraint of primary importance for modeling Galactic evolution and, in some cases, for studying the production of light nuclei in the early universe. The foil collection technique offers a direct way to measure some local interstellar gas abundances. With this method thin metal foils are exposed to the flux of neutral interstellar particles. Particles with sufficient energy penetrate the foil and remain trapped within its atomic structure. With the COLLISA experiment we have used this technique to collect a sample of interstellar neutral matter with the aim of determining the helium isotopic ratio in the LISM. The foils were exposed on board the Russian space station Mir. After exposure in space, the foils were brought back to the Earth, and the amount of captured particles was determined by mass spectrometric analysis at the University of Bern. The analysis has allowed the detection of interstellar 3He and 4He and the determination of the LISM isotopic number ratio 3He/4He = (1.7 ± 0.8) × 10-4. This value is consistent with protosolar ratios obtained from meteorites and Jupiters atmosphere, supporting the hypothesis that negligible changes of the abundance of 3He occurred in the Galaxy during the past 4.5 Gyr.

Interstellar helium trapped with the collisa experiment on the MIR space station-improved isotope analysis by in vacuo etching

We have redetermined the helium isotopic composition of the local interstellar cloud (LIC) in the framework of the Swiss-Russian Collection of Interstellar Atoms (COLLISA) collaboration. Based on in vacuo etching analyses of foils that have been exposed to the interstellar neutral particle flux on board the Mir space station, we obtain (3He/4He)LIC = (1.62 ± 0.29) × 10-4. This is the most precise determination of the He isotopic composition of the LIC, with errors being lower by more than a factor of 2 compared to an earlier experiment on similar foils and compared to the analysis of interstellar pick-up ions. Comparing our improved result with current models of Galactic chemical evolution reveals that close to 100% of all Galactic low-mass stars must have undergone extra mixing associated with cool bottom processing. The 3He abundance relative to 4He in the LIC is within the uncertainty identical to the value of (1.66 ± 0.06) × 10-4 inferred for the protosolar cloud (PSC), showing that no significant evolution of the 3He abundance took place since 4.6 Gyr ago at the solar distance (~8 kpc) from the Galactic center. Our value sets new rigorous constraints on Galactic evolution models. Since the Big Bang nucleosynthesis theory predicts a value of ≤(1.1 ± 0.2) × 10-4, a noticeable increase of the relative abundance of 3He has apparently occurred in the Galaxy before the formation of the solar system, but, contrary to earlier expectations, only a modest or negligible increase is registered after the formation of the solar system.

Direct Measurement of 3He/4He in the LISM with the COLLISA experiment

Results from direct measurements of the helium isotopic ratio in the closest regions of the Local Intersteller Medium (LISM) are presented. Neutral 3He and 4He atoms coming from the LISM were captured in space by means of the foil collection technique, a method already successfully used during the Apollo missions to determine the noble gas isotopic ratios in the solar wind. In the framework of the Swiss-Russian project COLLISA (COLLection of InterStellar Atoms), beryllium-copper foils were placed on the outer surface of the space station Mir and directly exposed to the flux of interstellar neutrals. The neutral particles of the LISM cross the heliopause and reach, almost unaltered, the Mir orbit at 400 km height above the Earth. Here, the kinetic energy of the interstellar flux ramming against the foils is sufficient to trap the particles into the atomic structure of the metal. After an exposure of ∼60 hours, the foils were recovered by the cosmonauts and brought back to Earth by the American space shuttl...

3 He and 4 He in the local interstellar gas as observed with the COLLISA foil experiment on the Mir space station

With the COLLISA foil experiment onboard the Mir space station we have collected samples of interstellar helium, which have been returned to the Earth and investigated by mass spectrometric analysis. Recently, we have been able to reduce the experimental uncertainties as given earlier (Salerno et al. 2003). Our improved estimate of the helium isotopic ratio in the local interstellar medium is now (