Solar wind contribution to surficial lunar water: Laboratory investigations

Burke, Daren J.; Dukes, C. A.; Kim, J.-H.; Shi, J.; Famá, M.; Baragiola, R. A.

doi:10.1016/j.icarus.2010.11.007

Cited by 52 publications

(46 citation statements)

References 29 publications

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“…Similar cation depletions and oxygen excesses are observed in amorphous rims produced during laboratory irradiation of crystalline silicate standards using H + and He + ions at SW fluences (12). * Previous attempts to detect water in rims on the surfaces of irradiated oxygen-rich minerals using bulk analytical methods, where water, if present, is close to detection limits, have yielded conflicting results (13,14). We used valence electron energy-loss spectroscopy (VEELS) because its ability to detect water in situ at the nanoscale has been demonstrated in aqueous liquids, biomaterials, and ices (15-17).…”

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confidence: 99%

Detection of solar wind-produced water in irradiated rims on silicate minerals

Bradley

Ishii

Gillis-Davis

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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The solar wind (SW), composed of predominantly ∼1-keV H + ions, produces amorphous rims up to ∼150 nm thick on the surfaces of minerals exposed in space. Silicates with amorphous rims are observed on interplanetary dust particles and on lunar and asteroid soil regolith grains. Implanted H + may react with oxygen in the minerals to form trace amounts of hydroxyl (−OH) and/or water (H 2 O). Previous studies have detected hydroxyl in lunar soils, but its chemical state, physical location in the soils, and source(s) are debated. If −OH or H 2 O is generated in rims on silicate grains, there are important implications for the origins of water in the solar system and other astrophysical environments. By exploiting the high spatial resolution of transmission electron microscopy and valence electron energy-loss spectroscopy, we detect water sealed in vesicles within amorphous rims produced by SW irradiation of silicate mineral grains on the exterior surfaces of interplanetary dust particles. Our findings establish that water is a byproduct of SW space weathering. We conclude, on the basis of the pervasiveness of the SW and silicate materials, that the production of radiolytic SW water on airless bodies is a ubiquitous process throughout the solar system. solar wind radiolysis | prebiotic water | cosmic dust | astrobiology | aberration-corrected scanning transmission electron microscopy T here are two principal space weathering processes, solar wind (SW) ion irradiation and micrometeorite impacts, that produce rims on exposed mineral surfaces (1). Our focus here is on SW irradiation because of its possible connection to the production of water and hydroxyl radicals (2-5). Space-weathered rim thicknesses vary with the densities of implanted solar flare (SF) tracks, and track densities depend on the exposure ages of individual interplanetary dust particles (IDPs) in space. On lunar soil grains and grains on surfaces of IDPs, rims are typically 75-150 nm thick with SF track densities of 10 10 -10 11 cm −2 that are consistent with 10 4 -to 10 5 -y SW exposure ages (6, 7) ( Fig. 1 B-D). Rims on asteroid Itokawa regolith grains are 30-60 nm thick with SF track densities of 5 × 10 9 cm −2 that are consistent with ∼10 3 -y exposure ages (8) (Origins and Properties of Rims on IDPs, Asteroid Itokawa, and Lunar Soil Grains). This correlation between amorphous rim thicknesses and SF track densities indicates that SW irradiation is the primary mechanism for amorphous rim formation. We examine rims on surface grains in IDPs because they are solely due to SW irradiation, whereas rims on lunar soil grains are due to SW irradiation, impact vapor deposition, or a combination of both (9), and remote observations suggest that if water is indeed produced in rims on lunar soil grains, it is not efficiently retained (10). Typical 5-to 25-μm diameter chondritic porous (CP) IDPs are low-density aggregates of predominantly submicrometer-sized grains, and they are collected in the stratosphere (11) (Fig. 1 A-D and Origins of CP IDPs). Chemical ana...

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mentioning

confidence: 99%

Detection of solar wind-produced water in irradiated rims on silicate minerals

Bradley

Ishii

Gillis-Davis

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…However, because the irradiations were not done under ultra-high vacuum conditions and samples were exposed to air several times during the experiment, and additionally because of possible contamination of the ion beam with OH + (OD + ) ions in both studies, the assertion that ion irradiation under lunar conditions can produce sufficient OH to account for the remote IR observations of the Moon remained questionable. Meanwhile, Burke et al (2011), using thin slabs of terrestrial ilmenite and anorthite under UHV, obtained an upper limit on OH production that predicted lunar absorption band depths in the Moon of no more than 0.5% reflectance or ~2x10 16 OH/cm 2 , much lower than the remote lunar measurements of 3-14% reflectance.…”

Section: Astrophysical Motivationmentioning

confidence: 99%

“…Irradiations were performed at normal incidence with energies in the range of 2 -5 keV, slightly higher than the average solar wind energy (~1 keV) but still within typical ranges. Previous experiments were done using 2 keV H2 + ions which were expected to split on contact with the surface with an equal amount of energy (1keV) partitioned to each atom [Burke, et al, 2011;Ichimura, et al, 2012]. In the current experiments, the use of a mass analyzed beam means that it is unnecessary to assume that the OH production is the same for protons (H + ) and two-correlated hydrogen (H2 + ).…”

Section: Ion Implantation Into Minerals and A-sio2mentioning

confidence: 99%

“…The sensitivity of the FTIR measurements was ~3x10 -4 absorbance in transmission, corresponding to ~1x10 15 OH/cm 2 . Using a room temperature DTGS detector eliminated uncertainty due to water condensed on LN2 cooled detectors as seen in previous studies [Theocharous, 2005;Burke et al, 2011]. Infrared spectra were taken from 5000-500 cm -1 at a resolution of 8 cm -1 and averaged over 1024 scans for a high signal 0.36 mm to noise ratio.…”

Section: Ion Implantation Into Minerals and A-sio2mentioning

confidence: 99%

“…As mentioned above, one of the explanations offered for discrepancies in the measured hydroxyl production between the experiments of Burke et al (2011) and Ichimura et al (2012) was the exposure of irradiated samples to atmospheric air in the latter. To test the effects of background gas exposure during and after irradiation, samples were irradiated with He + and Ar + and subsequently exposed to background H2 gas or atmospheric air.…”

Section: Sample Exposure To H2 and Atmospherementioning

confidence: 99%

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The Role of Solar Wind in the Formation of Hydroxyl on Airless Silicate Bodies in Space

Schaible

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Dedicated to all individuals who work for the betterment of themselves, their world, and their connection with the oneness that binds us all. To all my family and friends that have seen my needs and helped me to the position I am in, thank you. AbstractStudies of the interaction of solar radiation with the surfaces of moons, asteroids and comets can provide fundamental information about the early history of our solar system and help elucidate the ways in which such systems evolve. Airless bodies in space such as the Moon, asteroids and interplanetary dust particles are subject to bombardment from energetic solar wind electrons and ions, ultraviolet photons, micrometeorites and cosmic rays. This process is known as space weathering and the cumulative effect of the radiation modifies the chemical and physical nature of the ices and minerals that make up such surfaces. The work presented here investigates the interaction of solar wind hydrogen and helium with analog minerals and lunar soil using infrared spectroscopy (FTIR), mass spectrometry (SIMS), and optical photometry. Experiments were performed under Ultra High Vacuum (UHV) pressures and over a temperature range of 15 K to 400 K to simulate lunar surface conditions, and radiation was performed using a mass analyzed ion accelerator that allowed samples to be irradiated with specific ions at energies in the range of the solar wind.

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Hydrogen implantation in silicates: The role of solar wind in SiOH bond formation on the surfaces of airless bodies in space

Schaible

Baragiola

2014

JGR Planets

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Hydroxyl on the lunar surface revealed by remote measurements has been thought to originate from solar wind hydrogen implantation in the regolith. The hypothesis is tested here through experimental studies of the rate and mechanisms of OH bond formation due to H + implantation of amorphous SiO 2 and olivine in ultrahigh vacuum. . The initial conversion rate of implanted H + into hydroxyl species was found to be~90% and decreased exponentially with fluence. There was no evidence for molecular water formation due to proton irradiation. Translating the laboratory measurements in thin plate samples to the granular lunar regolith, it is estimated that the measurements can account for a maximum of 17% relative OH absorption in reflectance spectroscopy of mature soils, consistent with spacecraft observations in the infrared of the Moon.

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Solar wind contribution to surficial lunar water: Laboratory investigations

Cited by 52 publications

References 29 publications

Detection of solar wind-produced water in irradiated rims on silicate minerals

Detection of solar wind-produced water in irradiated rims on silicate minerals

The Role of Solar Wind in the Formation of Hydroxyl on Airless Silicate Bodies in Space

Hydrogen implantation in silicates: The role of solar wind in SiOH bond formation on the surfaces of airless bodies in space

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