Desorption of alkali atoms and ions from oxide surfaces: Relevance to origins of Na and K in atmospheres of Mercury and the Moon

Madey, Theodore E.; Yakshinskiy, B. V.; Ageev, V. N.; Johnson, R. E.

doi:10.1029/98je00230

Cited by 141 publications

(129 citation statements)

References 98 publications

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“…Sputter-ing of the lunar surface has also been suggested to contribute subsidiarily to creation of the lunar Na atmosphere by enhancing diffusion of Na to the ground surface. Laboratory work also concluded that a photon-stimulated process could achieve a yield and kinetic temperature of the Na atmosphere consistent with previous observations (Madey et al, 1998;Yakshinskiy and Madey, 1999). On the other hand, optical observations by Flynn and Stern (1996) and by Stern et al (1997) did not detect Si, Al, Ca, Mg, Fe and Ti, or Al, Si, Mg and Mg + , respectively, and hence the researchers could only estimate the upper limits of their number densities.…”

Section: Introductionsupporting

confidence: 53%

Estimation of picked-up lunar ions for future compositional remote SIMS analyses of the lunar surface

Yokota

Saito

2005

Earth Planet Sp

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In situ measurement of Moon-originating ions picked-up in orbit round the Moon is expected to provide valuable information regarding the thin lunar atmosphere and surface. Secondary ions sputtered by the solar wind ions reflect the surface abundance. Global composition mapping of the lunar surface may be thus achieved by measuring the sputtered ions as one would perform laboratory SIMS. We studied the dynamics of picked-up lunar ions when the Moon was exposed to the solar wind. Our model's source mechanism involved photoionization of the lunar exospheric atoms, photon-stimulated ion desorption, and ion sputtering. We propose that an intense flux of picked-up lunar ions (10 4 /cm 2 sec) exists at an altitude of 100 km, for nearly a quarter of the orbit. The ion flux originating from the lunar surface is mono-directional and mono-energetic, and is distinguishable from that of lunar atmospheric origin whose energy spectra correspond to their spatial distribution. Our calculation suggested that ion measurements in orbit round the Moon enable remote SIMS analyses.

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Section: Introductionsupporting

confidence: 53%

Estimation of picked-up lunar ions for future compositional remote SIMS analyses of the lunar surface

Yokota

Saito

2005

Earth Planet Sp

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“…Ambient atoms were assumed to be physisorbed with weak van der Waals forces and a binding energy less than 0.5 eV . However, as shown by Madey et al (1998), the difference between the ambient and source populations in the regolith is not as large as suggested by Hunten et al (1988), since the returning Na mostly reabsorbs in an ionic form with the binding energy determined by the local defect density. …”

mentioning

confidence: 73%

“…Source atoms are chemically bonded to the grains with strong chemical bonds between the substrate and the absorbing atoms. These are predominantly ionically bonded to the oxygen in a bulk silicate (Madey et al 1998) with a binding energy larger than 0.5 eV. Ambient atoms were assumed to be physisorbed with weak van der Waals forces and a binding energy less than 0.5 eV .…”

mentioning

confidence: 99%

“…The second population was introduced in order to describe the source population of fresh atoms brought to the surface by meteoroid gardening or diffusion within grains. The binding energy distribution of this source population is chosen to be a Gaussian distribution between 2 and 3 eV and a most probable value of 2.5 eV (Madey et al 1998;). We also This scaling implies that the total sodium ejection rate is 25% of the rate if the nominal surface was permanently bombarded.…”

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confidence: 99%

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Mercury exosphere I. Global circulation model of its sodium component

Leblanc

Johnson

2010

Icarus

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Our understanding of Mercury's sodium exosphere has improved considerably in the last 5 years thanks to new observations (Schleicher et al. 2004) and to the publication of a summary of the large set of ground based observations (Potter et al. 2008;2007;. In particular, the non-uniformity in longitude of the dayside sodium distribution (the dawn/dusk asymmetry) has now been clearly observed. This suggests that Mercury's sodium exosphere is partly driven by a global day to night side migration of the volatiles. One of the key questions remaining is the nature of the prevailing sodium ejection mechanisms. Because of the uncertain parameters for each ejection mechanisms, solving this problem has been difficult as indicated by the numerous papers over the last 15 years with very different conclusions. In addition, the variation of the size and of the spatial distribution of the surface reservoir varies with distance from the sun affecting the importance of each ejection mechanism on Mercury's orbital position We here present an updated version of the model. We take into account the two populations of sodium in the surface reservoir , one ambient population (physisorbed in the regolith with low binding energy) and one source population (chemisorbed coming from grain interior or from fresh dust brought to the surface and characterized by a higher binding energy). We also incorporate a better description of the solar wind sputtering variation with solar conditions. The results of a large number of simulations of the sodium exosphere are compared with the measured annual cycle of Mercury sodium emission brightness. These measurements were obtained from the published data by Potter et al. (2007) as well as from our own data obtained during the last two years using THEMIS solar telescope. These data show that: the annual cycle in the emission brightness is roughly the same from one year to another; there are significant discrepancies ACCEPTED MANUSCRIPT3 between what would be observed if the exospheric content were constant; and t the annual cycle of Mercury's sodium exosphere strongly depends on its position in its orbit so that there are seasons in Mercury's exosphere.Based on these comparisons we derived the principal signatures for each ejection mechanism during a Mercury year and show that none of the ejection mechanisms dominates over the whole year. Rather, particular features of the annual cycle of the sodium intensity appear to be induced by one, temporarily dominant, ejection mechanism. Based on this analysis, we are able to roughly explain the annual cycle of Mercury's exospheric sodium emission brightness.We also derive a set of parameters defining those ejection mechanisms which best reproduce this cycle. For our best case, Mercury's exosphere content varies from ~1.6±0.1×10 28 Na atoms at TAA=140° and 70° respectively to ~4.5±0.3×10 28 Na atoms at TAA=180° and 0°. In addition, Mercury's exospheric surface reservoir contains ~1×10 31 Na atoms at TAA=300° and at TAA=170° with up to three times more so...

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“…Different mechanisms and source processes have been proposed as possible sources of the sodium and potassium (Hunten & Sprague 1997;Killen & IP 1999), including sputtering by the solar wind, photon-stimulated desorption (Madey et al 1998;Mendillo et al 1999;Yakshinskiy & Madey 2004), thermal desorption (Yakshinskiy & Madey 2000), and micrometeoritic impacts (Cintala 1992;Mendillo & Baumgardner 1995;Cremonese & Verani 1997;Verani et al 1998;Smith et al 1999).…”

Section: Introductionmentioning

confidence: 99%

Micrometeoroids flux on the Moon

Cremonese

Borin

Lucchetti

et al. 2013

A&A

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Context. The Moon has a tenuous exosphere consisting of atoms that are ejected from the surface by energetic processes, including hypervelocity micrometeoritic impacts, photon-stimulated desorption by UV radiation, and ion sputtering. Aims. We calculate the vapor and neutral Na production rates on the Moon caused by impacts of meteoroids in the radius range of 5−100 μm. We considered a previously published dynamical model to compute the flux of meteoroids at the heliocentric distance of the Moon. Methods. The orbital evolution of dust particles of different sizes is computed with an N-body numerical code. It includes the effects of Poynting-Robertson drag, solar wind drag, and planetary perturbations. The vapor production rate and the number of neutral atoms released in the exosphere of the Moon are computed with a well-established formulation. Results. The result shows that the neutral Na production rate computed following our model is higher than previous estimates. This difference can be due to the dynamical evolution model that we used to compute the flux and also to the mean velocity, which is 15.3 km s −1 instead of 12.75 km s −1 as reported in literature. Conclusions. Until now, the micrometeoritic impacts have been considered a negligible source for the release of neutral sodium atoms into the exosphere compared to other mechanisms, but according to our calculations, the contribution may be 8% of the photostimulated desorption at the subsolar point, becoming similar in the dawn and dusk regions and dominant on the night side.

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Desorption of alkali atoms and ions from oxide surfaces: Relevance to origins of Na and K in atmospheres of Mercury and the Moon

Cited by 141 publications

References 98 publications

Estimation of picked-up lunar ions for future compositional remote SIMS analyses of the lunar surface

Estimation of picked-up lunar ions for future compositional remote SIMS analyses of the lunar surface

Mercury exosphere I. Global circulation model of its sodium component

Micrometeoroids flux on the Moon

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