Note: This article was originally published with an incorrect version of the Acknowledgments, which appeared on p. 218 of the print version. The correct version of the Acknowledgments appeared on pp. 1–2. The corrected article is available below.

/pdf/human-health-risk-assessment-for-aluminium-aluminium-oxide-5dfetd69xm.pdf

Human Health Risk Assessment for Aluminium, Aluminium Oxide, and Aluminium Hydroxide

The variety of evidence bearing on the nature of space weathering is reviewed. The effects of space weathering include spectral darkening, reddening and subdued absorption bands, and the distinctive magnetic electron spin resonance caused by single-domain metallic iron particles. Ever since the Apollo missions, two paradigms have dominated the thinking of the planetary science community concerning space weathering: (1) the optical effects are caused by impact-vitrified glass in agglutinates, and (2) the submicroscopic metallic iron results from the reduction of ferrous iron by the impact melting of minerals whose surfaces have been saturated with hydrogen from the solar wind. However, studies carried out since the Apollo program showed that both of these paradigms are invalid. A hypothesis first suggested by the author and his colleagues 26 years ago, but not generally accepted at that time, now appears to be essentially correct: Both the optical and magnetic effects are caused by metallic iron particles smaller than the wavelength in ubiquitous vapor-deposited coatings on soil particle surfaces and inside agglutinates. The vapor is generated by both solar wind sputtering and micrometeorite impact vaporization and injected preferentially downward into the porous regolith. The iron is reduced by a physical process, the selective loss of oxygen that occurs during deposition of the vapor, and does not require heating, melting, or a reducing environment. A mathematical theory that describes the optical effects of the submicroscopic iron quantitatively is derived and applied to the regoliths of the Moon, Mercury and an S asteroid.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JE001338

Space weathering from Mercury to the asteroid belt

Energy levels of A = 21−44 nuclei (V)

Structure and properties of cast binary Ti-Mo alloys.

— Using new techniques to examine the products of space weathering of lunar soils, we demonstrate that nanophase reduced iron (npFe0) is produced on the surface of grains by a combination of vapor deposition and irradiation effects. The optical properties of soils (both measured and modeled) are shown to be highly dependent on the cumulative amount of npFe0, which varies with different starting materials and the energetics of different parts of the solar system. The measured properties of intermediate albedo asteroids, the abundant S-type asteroids in particular, are shown to directly mimic the effects predicted for small amounts of npFe0 on grains of an ordinary chondrite regolith. This measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1945-5100.2000.tb01496.x

Space weathering on airless bodies: Resolving a mystery with lunar samples

To date, areas contaminated by radionuclides discharged from the Fukushima Dai-ichi nuclear power plant accident have been mapped in detail. However, size of the radionuclides and their mixing state with other aerosol components, which are critical in their removal from the atmosphere, have not yet been revealed. We measured activity size distributions of 134Cs and 137Cs in aerosols collected 47 days after the accident at Tsukuba, Japan, and found that the activity median aerodynamic diameters of 134Cs and 137Cs in the first sample (April 28–May 12) were 0.54 and 0.53 μm, respectively, and those in the second sample (May 12–26) were both 0.63 μm. The activity size distributions of these radiocesium were within the accumulation mode size range and almost overlapped with the mass size distribution of non-sea-salt sulfate aerosol. From the analysis of other aerosol components, we found that sulfate was the potential transport medium for these radionuclides, and resuspended soil particles that attached radion...

Sulfate aerosol as a potential transport medium of radiocesium from the Fukushima nuclear accident.

For the purpose of simulating the surface alteration process called “space weathering”, experiments of pulse laser irradiation, proton implantation, and laser irradiation to proton implanted samples were performed and reflectance spectra of altered materials were measured. To simulate the impact heating by micrometeorite bombardments, we made a new apparatus using a pulse laser whose pulse duration is 6‐8 nanoseconds, comparable with a timescale of micrometeorite impacts. We find that the degree of space weathering, i.e., change of reflectance spectrum should depend on mineral composition. Laser irradiation onto olivine produces the largest reduction of albedo and the highest reddening of reflectance spectrum. In general, variation of olivine spectra is much larger than that of pyroxenes. Depths of absorption bands do not change in the scaled spectra. The olivine spectrum after the laser irradiation can match spectra of some olivine asteroids within a subtype of S-type asteroids. Comparison of Vesta spectrum with altered pyroxene spectra suggests that Vesta surface would be relatively older than olivine asteroids. We also investigate the influence of solar wind proton and pyroxene FeO content. The proton implantation causes small changes in olivine and enstatite spectra. Implanted protons do not influence spectral change by the laser irradiation: the laser irradiation and the proton implantation do not produce multiplicative but additive changes on the reflectance spectra. FeO content of pyroxenes does not relate to the degree of reflectance change.

/pdf/simulation-of-space-weathering-of-planet-forming-materials-3vwe7fkvyj.pdf

Simulation of space weathering of planet-forming materials: Nanosecond pulse laser irradiation and proton implantation on olivine and pyroxene samples

Thin film formation using the process of spin coating is investigated. The liquid film and surrounding gas phase two‐dimensional (2‐D) full governing equations with applicable boundary conditions are formulated. The heat and mass transfer that occurs in the gas and liquid phase and across the free surface, including the evaporation of solvent, are taken into account. The governing equations and boundary conditions are then reduced to a 1‐D case based on the variables radial dependency. The detailed film formation process that commences at the start of the spinning and ends with the dry‐up of the coated film is numerically simulated by utilizing the 1‐D governing equations. The complex effects of various process parameters, e.g., spinning speed, initial solute concentration, and disk heating, are clarified by the present numerical analysis. It was found that the final film thickness is mainly determined at the time when the film thinning rate resulting from radial convection has the same order as the film thinning rate resulting from solvent evaporation.

The film formation dynamics in spin coating

To investigate the etiology of Alzheimer’s disease, we administered aluminum to healthy rats and examined the aluminum uptake in the brain and isolated brain cell nuclei by particle-induced X-ray emission (PIXE) analysis. Ten days after the last injection, Al was detected in the rat brain and in isolated brain cell nuclei by PIXE analysis. Al was also demonstrated in the brain after 15 months of oral aluminum administration. Moreover, Al was detected in the brain and isolated brain cell nuclei from the patients with Alzheimer’s disease. Silver impregnation studies revealed that spines attached to the dendritic processes of cortical nerve cells decreased remarkably after aluminum administration. Electron microscopy revealed characteristic inclusion bodies in the hippocampal nerve cells 75 days after the injection. These morphological changes in the rat brain after the aluminum administration were similar to those reportedly observed in the brain of Alzheimer’s disease patients. Our results indicate that Alzheimer’s disease is caused by irreversible accumulation of aluminum in the brain, as well as in the nuclei of brain cells.

Hideo Ohashi

Papers

Sulfate aerosol as a potential transport medium of radiocesium from the Fukushima nuclear accident.

Simulation of space weathering of planet-forming materials: Nanosecond pulse laser irradiation and proton implantation on olivine and pyroxene samples

The film formation dynamics in spin coating

Aluminum neurotoxicity in the rat brain

Antarctic micrometeorites collected at the Dome Fuji Station