The Role of Solar Wind Ion Processing in Space Weathering of Olivine: Unraveling the Paradox of Laboratory Irradiation Results Compared to Observations of Natural Samples

Ion irradiation by the solar wind plays a major role in space weathering. Among its multiple effects are ion damage and implantation processes that alter the crystal structure as well as chemical composition of the outer few 100 nanometers of space exposed regolith grains. This forms a portion of the space weathered rims on lunar and asteroidal regolith grains that is uniquely ion-processed. One aspect of these ion-processed grain rims is the possible link between their widths, and degree of ion damage, and the length of exposure of their host grain on the topmost surface of lunar and asteroidal regoliths. Ultimately, quantifying this link relies on laboratory ion irradiation experiments to calibrate the ion fluence or dose at which different degrees and depths of ion damage occur. Here we discuss evidence, specifically from the mineral olivine, suggesting there may be limitations in extrapolating the results of laboratory ion irradiation experiments to natural ion irradiation by the solar wind

Distribution of warm water alpheoid shrimp (crustacea, caridea) on the continental shelf of eastern south america between 23 and 35º lat. S

The southern boundaries of Tozeuma serratum A. Milne Edwards, Salmoneus ortmanni (Rankin) and Processa profunda Manning & Chace, previously known only from the northwestern Atlantic, have been extended to São Paulo, Paraná and Uruguay, respectively. Latreutes parvulus (Stimpson), previously not known beyond São Paulo has been found to as far south as the Province of Buenos Aires. A systematic account of these four species is furnished, based mainly on material collected by the R/V "Prof. W. Besnard". The 16 species of Alpheoidea whose southern boundaries occur in warm-temperate shelf waters of eastern South America belong to two distinct faunal assemblages: (1) Tropical species - Alpheus floridanus Kingsley, A. intrinsecus Bate, A. normanni Kingsley, Salmoneus ortmanni (Rankin) Synalpheus longicarpus (Herrick), Ogyrides alphaerostris (Kingsley) (= O. occidentalis(Ortmann)), Exhippolysmata oplophoroides (Holthuis), Latreutes parvalus (Stimpson), Processa bermudensis (Rankin) and P. hemphilli Manning & Chace - which are largely restricted to coastal and inshore shelf waters less than 50 m deep; and (2) Subtropical species - Alpheus pouang Chris toffersen, A. puapeba Christoffersen, Merhippolyte americana Holthuis, Tozeuma serratum A. Milne Edwards, Processa guyanae. Holthuis and P. profunda Manning & Chace - which are largely restricted to the outer portion of the continental shelf within the studied area. Considering the temperature and distributional data available for each species, it is suggested that the poleward boundaries of O. alphaerostris are set by maximum summer temperatures of about 20ºC required for the reproduction of the species, while the poleward boundaries of most of the tropical and subtropical species are set by minimum winter temperatures critical for their survival: about 15ºC for A. floridanus, about 11ºC for E. oplophoroides, about 9ºC for A. pouang, L. parvulus, P. guyanae., P. guyanae and P. hemphilli, and P. profunda and about 8ºC for A. puapeba and M. americana. It is further suggested that the shoreward boundaries of some of the subtropical species are set by maximum summer temperatures critical for their survival: about 20-22ºC for A. puapzba and about 17-18ºC for A. pouang and M. americana

Phylogenetic relationships between Oplophoridae, Atyidae, Pasiphaeidae, Alvinocarididae Fam. N., Bresiliidae, Psalidopodidae and Disciadidae (Crustacea caridea atyoidea)

Os Pasiphaeoidea syn.n., Psalidopodoidea syn.n. e Bresilioidea syn.n. foram incluídos nos Atyoidea (mais correntemente conhecidos como Oplophoroidea), para se obter um conceito natural deste táxon. A monofilia do táxon Atyoidea emendado é indicado pelo exópodo reduzido do primeiro maxilípede. Uma hierarquia de 20 subgrupos monofiléticos, delimitados por 42 novidades evolutivas hipotéticas, é sintetizada num cladograma. A seguinte classificação filogenética sequenciada é proposta: Superfamília Atyoidea; Família Oplophoridae; Família Atyidae; Subfamília Xiphocaridinae; Gênero Xiphocaris; Subfamília Atyinae; Família Pasiphaeidae; Família Alvinocarididae fam.n.; Gênero Alvinocaris; Família Bresiliidae; Gênero Bresilia; Família Psalidopodidae; Gênero Psalidopus; Família Disciadidae; Gênero Pseudocheles; Gênero Lucaya; Gênero Tridiscias; Gênero Discias

Space Plasma Ion Processing of Ilmenite in the Lunar Soil: Insights from In-Situ TEM Ion Irradiation Experiments

Space weathering on the moon and asteroids results largely from the alteration of the outer surfaces of regolith grains by the combined effects of solar ion irradiation and other processes that include deposition of impact or sputter-derived vapors. Although no longer considered the sole driver of space weathering, solar ion irradiation remains a key part of the space weathering puzzle, and quantitative data on its effects on regolith minerals are still in short supply. For the lunar regolith, previous transmission electron microscope (TEM) studies performed by ourselves and others have uncovered altered rims on ilmenite (FeTiO3) grains that point to this phase as a unique "witness plate" for unraveling nanoscale space weathering processes. Most notably, the radiation processed portions of these ilmenite rims consistently have a crystalline structure, in contrast to radiation damaged rims on regolith silicates that are characteristically amorphous. While this has tended to support informal designation of ilmenite as a "radiation resistant" regolith mineral, there are to date no experimental data that directly and quantitatively compare ilmenite s response to ion radiation relative to lunar silicates. Such data are needed because the radiation processed rims on ilmenite grains, although crystalline, are microstructurally and chemically complex, and exhibit changes linked to the formation of nanophase Fe metal, a key space weathering process. We report here the first ion radiation processing study of ilmenite performed by in-situ means using the Intermediate Voltage Electron Microscope- Tandem Irradiation facility (IVEM-Tandem) at Argonne National Laboratory. The capability of this facility for performing real time TEM observations of samples concurrent with ion irradiation makes it uniquely suited for studying the dose-dependence of amorphization and other changes in irradiated samples

Solar Ion Processing of Itokawa Grains: Reconciling Model Predictions with Sample Observations

Analytical TEM observations of Itokawa grains reported to date show complex solar wind ion processing effects in the outer 30-100 nm of pyroxene and olivine grains. The effects include loss of long-range structural order, formation of isolated interval cavities or "bubbles", and other nanoscale compositional/microstructural variations. None of the effects so far described have, however, included complete ion-induced amorphization. To link the array of observed relationships to grain surface exposure times, we have adapted our previous numerical model for progressive solar ion processing effects in lunar regolith grains to the Itokawa samples. The model uses SRIM ion collision damage and implantation calculations within a framework of a constant-deposited-energy model for amorphization. Inputs include experimentally-measured amorphization fluences, a Pi steradian variable ion incidence geometry required for a rotating asteroid, and a numerical flux-versus-velocity solar wind spectrum

Space Plasma Ion Processing of the Lunar Soil: Modeling of Radiation-Damaged Rim Widths on Lunar Grains

Chemically and microstructurally complex altered rims around grains in the finest size fraction (<20 micron) of the lunar regolith are the result of multi-stage processes involving both solar ion radiation damage and nanoscale deposition of impact or sputter-derived vapors. The formation of the rims is an important part of the space weathering process, and is closely linked to key changes in optical reflectance and other bulk properties of the lunar surface. Recent application of field-emission scanning transmission electron microscope techniques, including energy dispersive X-ray spectral imaging, is making it easier to unravel the "nano-stratigraphy" of grain rims, and to delineate the portions of rims that represent Radiation-Amorphized (RA) host grain from overlying amorphous material that represents vapor/sputter deposits. For the portion of rims formed by host grain amorphization (henceforth called RA rims), we have been investigating the feasibility of using Monte Carlo-type ion-atom collision models, combined with experimental ion irradiation data, to derive predictive numerical models linking the width of RA rims to the grain s integrated solar ion radiation exposure time

Space Weathering of Olivine: Samples, Experiments and Modeling

Olivine is a major constituent of chondritic bodies and its response to space weathering processes likely dominates the optical properties of asteroid regoliths (e.g. S- and many C-type asteroids). Analyses of olivine in returned samples and laboratory experiments provide details and insights regarding the mechanisms and rates of space weathering. Analyses of olivine grains from lunar soils and asteroid Itokawa reveal that they display solar wind damaged rims that are typically not amorphized despite long surface exposure ages, which are inferred from solar flare track densities (up to 10 (sup 7 y)). The olivine damaged rim width rapidly approaches approximately 120 nm in approximately 10 (sup 6 y) and then reaches steady-state with longer exposure times. The damaged rims are nanocrystalline with high dislocation densities, but crystalline order exists up to the outermost exposed surface. Sparse nanophase Fe metal inclusions occur in the damaged rims and are believed to be produced during irradiation through preferential sputtering of oxygen from the rims. The observed space weathering effects in lunar and Itokawa olivine grains are difficult to reconcile with laboratory irradiation studies and our numerical models that indicate that olivine surfaces should readily blister and amorphize on relatively short time scales (less than 10 (sup 3 y)). These results suggest that it is not just the ion fluence alone, but other variable, the ion flux that controls the type and extent of irradiation damage that develops in olivine. This flux dependence argues for caution in extrapolating between high flux laboratory experiments and the natural case. Additional measurements, experiments, and modeling are required to resolve the discrepancies among the observations and calculations involving solar wind processing of olivine

Surface Exposure Ages of Space-Weathered Grains from Asteroid 25143 Itokawa

We use the observed effects of solar wind ion irradiation and the accumulation of solar flare particle tracks recorded in Itokawa grains to constrain the rates of space weathering and yield information about regolith dynamics. The track densities are consistent with exposure at mm depths for 104-105 years. The solar wind damaged rims form on a much faster timescale, <10(exp 3) years

Sampling the Uppermost Surface of Airless Bodies

The uppermost surface of an airless body is a critical source of ground-truth information for the various remote sensing techniques that only penetrate nanometers to micrometers into the surface. Such samples will also be vital for understanding conditions at the surface and acquiring information about how the body interacts with its environment, including solar wind interaction, grain charging and levitation [1]. Sampling the uppermost surface while preserving its structure (e.g. porosity, grain-to-grain contacts) however, is a daunting task that has not been achieved on any sample return mission to date

Solar Ion Processing of Major Element Surface Compositions of Mature Mare Soils: Insights from Combined XPS and Analytical TEM Observations

Solar wind ions are capable of altering the sur-face chemistry of the lunar regolith by a number of mechanisms including preferential sputtering, radiation-enhanced diffusion and sputter erosion of space weathered surfaces containing pre-existing compositional profiles. We have previously reported in-situ ion irradiation experiments supported by X-ray photoelectron spectroscopy (XPS) and analytical TEM that show how solar ions potentially drive Fe and Ti reduction at the monolayer scale as well as the 10-100 nm depth scale in lunar soils [1]. Here we report experimental data on the effect of ion irradiation on the major element surface composition in a mature mare soil