Sputtering Products of Sodium Sulfate: Implications for Io's Surface and for Sodium-Bearing Molecules in the Io Torus

Wiens, R. C.; Burnett, D. S.; Calaway, W. F.; Hansen, Chris S; Lykke, Keith R.; Pellin, Michael J.

doi:10.1006/icar.1997.5758

Cited by 53 publications

(61 citation statements)

References 29 publications

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“…A good analogue of the energy distribution of the SWS was measured in laboratory by Wiens et al (1997) for Na 2 SO 4 pressed-powder samples. Lammer et al (2003) The effect would be difficult to take into account without further laboratory studies.…”

Section: Discussionmentioning

confidence: 99%

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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Section: Discussionmentioning

confidence: 99%

Mercury exosphere I. Global circulation model of its sodium component

Leblanc

Johnson

2010

Icarus

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“…Yields are undoubtedly lower on an irradiated regolith due to the prolonged effect of irradiation, sticking and the "fairy castle" structure of a regolith. Ion sputtering of sodium sulfate (Na2SO4) and albite (NaSi3A1Os) has been studied with an Ar + ion beam [Wiens et al, 1997]. The sputter products of albite include oxides (NaO, A10, and SiO) and dimers (Na2, A12, and Si2) , and NaS, but not NaSi or NaA1.…”

Section: Composition Of the Surface And Corementioning

confidence: 99%

The surface‐bounded atmospheres of Mercury and the Moon

Killen¹,

Ip²

1999

Reviews of Geophysics

171

123

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Abstract. Surface-bounded exospheres have been detected at the Moon, Mercury, and Europa and almost certainly exist about other objects. Historically, the first of these systems to be observed was the lunar exosphere, where He and Ar were detected by the Apollo spacecraft. The Hermean exosphere is archetypical of these systems in that it is part of a coupled system including the surface and magnetosphere interacting dynamically with the solar wind and fields. Studies of the Hermean exosphere heretofore have neglected or only superficially considered these interactions. We will review the current state of knowledge of the exospheres of Mercury and the Moon and discuss areas in which our knowledge is most incomplete. We will focus on the exosphere as part of a coupled system including the surface at its base and the particle, field, and interplanetary environment as both a source and sink for neutrals. Apollo era instruments made unambiguous detections of 36mr, 4ømr, Early Work and OverviewIn a review prior to the Mariner 10 encounter, Banks et al. [1970] reported no observational evidence for the presence of an atmosphere about Mercury. They predicted an exosphere (N < 2 x 10 TM cm -2) or thin atmosphere resulting from diffusion or effusion from the interior, solar wind implantation with subsequent thermal evaporation, or sputtering. By scaling terrestrial noble gas production and diffusion rates and assuming a lunar-like solar wind interaction, they suggested that the most abundant constituents should be the noble gases derived from the solar wind and radiogenic sources, the most abundant being 4He, followed by 4øAr and 2øNe.

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“…Charged particle irradiation can preferentially deplete such materials of sodium (Wiens et al 1997, Chrisey et al 1988, Madey et al 1998, leaving behind, for instance, the frozen hydrated sulfuric acid (Johnson 2001) suggested by Galileo spacecraft data (Carlson et al 1999). Most of the ejected sodium atoms return to the surface but their large excursion distances lead to redistribution across the surface of Europa.…”

Section: Introductionmentioning

confidence: 97%