We have analyzed nitrogen, neon and argon abundances and isotopic ratios in target material exposed in space for 27
months to solar wind (SW) irradiation during the Genesis mission. SW ions were ...extracted by sequential UV (193
nm) laser ablation of gold-plated material, purified separately in a dedicated line, and analyzed by gas source static mass spectrometry. We analyzed gold-covered stainless steel pieces from the Concentrator, a device that concentrated SW ions by a factor of up to 50. Despite extensive terrestrial N contamination, we could identify a non-terrestrial,
15N-depleted nitrogen end-member that points to a 40% depletion of
15N in solar-wind N relative to inner planets and meteorites, and define a composition for the present-day Sun (
15N/
14N
=
2.26
±
0.67
×
10
−3, 2σ), which is indistinguishable from that of Jupiter’s atmosphere. These results indicate that the isotopic composition of nitrogen in the outer convective zone of the Sun has not changed through time, and is representative of the protosolar nebula. Large
15N enrichments due to e.g., irradiation, low temperature isotopic exchange, or contributions from
15N-rich presolar components, are therefore required to account for inner planet values.
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 NASA's 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.
Observations of interstellar pickup ions inside the heliosphere provide an indirect method to access information on the surrounding interstellar medium. The so‐called pickup ion focusing cone and ...pickup ion crescent, which show an imprint of the related longitudinal distribution of interstellar neutrals in form of two overabundances on the down‐ and upwind side of the sun, are both believed to be aligned along the inflow vector of the interstellar medium. By finding their longitudinal positions, we can give an accurate value for the inflow direction λISM of interstellar matter. For that we performed an epoch analysis of interstellar pickup ions measured by the PLAsma and SupraThermal Ion Composition instrument (PLASTIC) on the Solar TErrestrial RElations Observatory mission (STEREO) and were able to reveal in situ the longitudinal distribution of interstellar He+, O+, and Ne+ pickup ions in the ecliptic plane at 1 AU. The previously accepted values for the inflow direction of interstellar matter in ecliptic longitude, as obtained with Ulysses/GAS (λ = 75.4° ± 0.5°), Prognoz 6 (λ = 74.5° ± 1°), and ACE/SWICS (λ = 74.43° ± 0.33°), are currently debated, especially in view of recent results from the Interstellar Boundary Explorer (IBEX) mission that show an inflow direction of interstellar neutral helium of λ = 79° + 3.0°(−3.5°). Four years of data collected with PLASTIC aboard STEREO A provided statistics sufficient not only to obtain values for the inflow direction of interstellar helium (λCone = 77.4° ± 1.9° and λCrescent = 80.4° ± 5.4°, deduced from an analysis of the He+ focusing cone and crescent, respectively) but also to derive values for the inflow direction of interstellar neon (λCone = 77.4° ± 5.0° and λCrescent = 79.7° ± 2.6°) and oxygen (λCrescent = 78.9° ± 3.1°). Although our values for He+, O+, and Ne+ are consistent with results from ACE, Ulysses, and Prognoz 6, considering the statistical and systematic uncertainties (except λNe,Crescent), they are systematically larger than the previously accepted values of 74.99 ± 0.55° and show a better agreement with the values from IBEX.
Key Points
Determining the inflow direction of interstellar matter using a unique approach
Inflow directions of He+, Ne+, and O+ that are barely consistent with previous values
First time that Ne+ and O+ inflow could be determined independently
The Sun is the only star from which matter can be collected in order to investigate its elemental and isotopic composition. Solar elemental abundances provide the most important benchmark for the ...chemical evolution of the galaxy. They can be derived from photospheric observations, from in situ investigations of the solar wind, and from solar energetic particles. Solar isotopic abundances provide an important reference for the galactic evolution and if available with sufficient precision, also for the chemical and physical evolution of the solar system. The abundances of isotopes in the solar atmosphere can only be inferred from in situ observations of solar particles. This review makes an attempt to summarize current knowledge about the composition of the solar wind and shows how the elemental, isotopic, and charge state composition of solar wind particles is shaped as the solar corona expands throughout the heliosphere.
Minor ions in the solar wind Bochsler, Peter
The Astronomy and astrophysics review,
01/2007, Letnik:
14, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Ions heavier than 4 He are treated as "minors" in the solar wind. This is justified for many applications since minor ions have no significant influence on the dynamics of the interplanetary plasma. ...However, minor ions carry information on many aspects of the formation, on the acceleration and on the transfer of solar plasma from the corona into the interplanetary space. This review concentrates on various aspects of minor ions as diagnostic tracers. The elemental abundance patterns of the solar wind are shaped in the chromosphere and in the lower transition region by processes, which are not fully understood at this moment. Despite this lack of detailed understanding, observed abundance patterns have been classified and are now commonly used to characterize the sources, and to trace back solar-wind flows to their origins in the solar atmosphere. Furthermore, the solar wind is the most important source of information for solar isotopic abundances and for solar abundances of volatile elements. In order to fully exploit this information, a comprehensive understanding of elemental and isotopic fractionation processes is required. We provide observational clues to distinguish different processes at work. PUBLICATION ABSTRACT
Solar wind (SW) helium, neon, and argon trapped in a bulk metallic glass (BMG) target flown on NASA’s Genesis mission were analyzed for their bulk composition and depth-dependent distribution. The ...bulk isotopic and elemental composition for all three elements is in good agreement with the mean values observed in the Apollo Solar Wind Composition (SWC) experiment. Conversely, the He fluence derived from the BMG is up to 30% lower than values reported from other Genesis bulk targets or in-situ measurements during the exposure period. SRIM implantation simulations using a uniform isotopic composition and the observed bulk velocity histogram during exposure reproduces the Ne and Ar isotopic variations with depth within the BMG in a way which is generally consistent with observations. The similarity of the BMG release patterns with the depth-dependent distributions of trapped solar He, Ne, and Ar found in lunar and asteroidal regolith samples shows that also the solar noble gas record of extraterrestrial samples can be explained by mass separation of implanted SW ions with depth. Consequently, we conclude that a second solar noble gas component in lunar samples, referred to as the “SEP” component, is not needed. On the other hand, a small fraction of the total solar gas in the BMG released from shallow depths is markedly enriched in the light isotopes relative to predictions from implantation simulations with a uniform isotopic composition. Contributions from a neutral solar or interstellar component are too small to explain this shallow sited gas. We tentatively attribute this superficially implanted gas to low-speed, current-sheet related SW, which was fractionated in the corona due to inefficient Coulomb drag. This fractionation process could also explain relatively high Ne/Ar elemental ratios in the same initial gas fraction.
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.
On the origin of inner-source pickup ions Wimmer-Schweingruber, Robert F.; Bochsler, Peter
Geophysical research letters,
January 2003, Letnik:
30, Številka:
2
Journal Article
Recenzirano
In situ measurements of pickup ions (PUI) exhibit a component that has nearly thermalized with the solar wind. This implies an origin close to the Sun and is generally ascribed to interaction of the ...solar wind with interplanetary dust particles (IDPs). We propose a scenario for the origin of inner‐source PUIs in which a population of very small IDPs serves as the neutralizing agent for solar wind ions. The size of these IDPs is less than or comparable to the penetration range, of solar wind ions in IDP material. The interaction of the solar wind with such particles results in a net charge exchange in which solar wind ions exit the IDPs as predominantly neutral or singly‐charged ions. When the neutralized solar wind is reionized, it is picked up and can then be measured as a PUI.
In view of new observational evidence from isotope spectrometers on WIND, SOHO (Solar Heliospheric Observatory), and ACE (Advanced Composition Explorer), we explore the efficiency of isotope ...fractionation processes in the inner corona. We reinvestigate the role of Coulomb collisions in the acceleration of minor ions using a multifluid model. To model the main gas, we study stationary solutions for the continuity and momentum equations of electrons, protons, and alpha particles. As a closure of the system of equations, we prescribe expansion geometry and temperature profiles based on observations. The behavior of minor ions, which are treated as test particles, depends in a complicated manner on their mass and on their charge, structured by the interplay of acceleration, gravity, pressure gradient, electromagnetic fields, Coulomb drag, and thermal diffusion. We compare the fractionation effects in different solar wind regimes: In our model high‐speed solar wind emanating from polar coronal holes, Coulomb friction practically equalizes the velocities of all species, and no substantial fractionation takes place. In the case of a rapidly expanding magnetic field geometry, for example, in the vicinity of a coronal streamer, the proton flux and thus the Coulomb friction on minor ions is reduced, leading to depletion of heavy species in the solar wind. The model also predicts a substantial depletion of alpha particles relative to protons in the heliospheric current sheet, consistent with observations. In such a situation, heavy elements are depleted in the solar wind relative to protons as well, but the effect is strongest for alpha particles. Isotopic fractionation of helium of the order of 30% is possible, while the isotope effect on heavier elements amounts at most to a few percent per mass unit.
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