The Boundary of Alkali Surface Boundary Exospheres of Mercury and the Moon

Sarantos, M.; Tsavachidis, S.

doi:10.1029/2020gl088930

Cited by 20 publications

(17 citation statements)

References 30 publications

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“…Still, kinetic models in Fig. 4 Sarantos and Tsavachidis 2020) demonstrate that this geometric effect is only a partial explanation of the observed linewidth enhancement and consequently the Moon's exosphere is hotter at New Moon phases. concluded that the largest measured scale heights are at dawn and dusk, and are correlated with local solar time.…”

Section: Used Anmentioning

confidence: 92%

“…Our inability to explain the observed Na cycle suggests that current models of the surfaceexosphere interaction may be incomplete. Some progress towards a better specification of the boundary conditions for models was contained in the recent work of Sarantos and Tsavachidis (2020). To understand how the microstructure of soil affects the exospheric reservoir for alkalis, a simulation of a porous soil (1 mm in depth) was produced in that work using spherical grains sampled with a distribution of grain sizes from Apollo Lunar Soil Sample 72141, a typical mature soil (keeping in mind that Mercury's regolith is probably different from Moon's regolith, as an example, in composition).…”

Section: The Role Of the Surface Interaction With The Exospherementioning

confidence: 99%

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Comparative Na and K Mercury and Moon Exospheres

et al. 2022

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Sodium and, in a lesser way, potassium atomic components of surface-bounded exospheres are among the brightest elements that can be observed from the Earth in our Solar System. Both species have been intensively observed around Mercury, the Moon and the Galilean Moons. During the last decade, new observations have been obtained thanks to space missions carrying remote and in situ instrumentation that provide a completely original view of these species in the exospheres of Mercury and the Moon. They challenged our understanding and modelling of these exospheres and opened new directions of research by suggesting the need to better take into account the relationship between the surface-exosphere and the magnetosphere. In this paper, we first review the large set of observations of Mercury and the Moon Sodium and Potassium exospheres. In the second part, we list what it tells us on the sources and sinks of these exospheres focusing in particular on the role of their magnetospheres of these objects and then discuss, in a third section, how these observations help us to understand and identify the key drivers of these exospheres.

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Section: Used Anmentioning

confidence: 92%

Section: The Role Of the Surface Interaction With The Exospherementioning

confidence: 99%

Comparative Na and K Mercury and Moon Exospheres

et al. 2022

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“…When a particle was determined to stick to the surface, no subsequent desorption events were considered. It has been suggested that ∼60% of Na atoms that stick to the lunar regolith are lost to microscopic shadows on each bounce (Sarantos & Tsavachidis 2020). The model assumed that the Na source rate near the subsolar point is ∼2 × 10 6 Na atoms cm −2 s −1 (Sarantos et al 2010).…”

Section: Constraints On Exospheric Structurementioning

confidence: 99%

Selenographic and Local Time Dependence of Lunar Exospheric Sodium as Observed by LADEE

Dawkins¹,

Sarantos²,

Janches³

et al. 2022

Planet. Sci. J.

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Even though sodium (Na) has been known to be a constituent of the lunar exosphere for the past thirty years, limitations introduced by Earth-based observations make it difficult to determine how its distribution varies with local time. We used observations from the Ultraviolet and Visible Spectrometer instrument on board the NASA Lunar Atmosphere and Dust Environment Explorer mission to search for evidence of near-instantaneous dayside variation of exospheric Na across one lunation (2014 February–March). Through comparison with model simulations, the data appear to be consistent with persistent southern enhancements of Na, while no evidence of systematic depletion of the Na exosphere reservoir within two hours of local noon was obtained. The results indicate an enhancement of the gas density over Mare regions and the lunar nearside; though this finding could mean that the weak Na emission is lost in the scattering continuum over brighter soils. Day-to-day variability is observed and may reflect a changing solar wind and meteoroid environment combined with inhomogeneities in the gas–surface interaction parameters and Na distribution on the lunar surface. We found that, due to the limited viewing geometry and sensitivity of the instrument to scattering from the bright lunar surface, it is difficult to uniquely separate the latitudinal and local time variations of Na.

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“…Recent works have illustrated the need for more accurate simulations of the surfaceexosphere interaction in airless bodies. For example, Sarantos and Tsavachidis (2020) showed that the mobility of alkalis (Na and K) on the surface of regolith grains on both the Moon and Mercury reduce the overall desorption of these species from these grains. On the Moon, this effect might explain why the sodium exosphere reacts more slowly to the changes of the micrometeoroid flux compared to potassium, because the latter, being more massive than the former, has an overall reduced surface mobility, and therefore a higher chance to be photodesorbed.…”

Section: Simulationsmentioning

confidence: 99%

Volatiles and Refractories in Surface-Bounded Exospheres in the Inner Solar System

et al. 2021

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Volatiles and refractories represent the two end-members in the volatility range of species in any surface-bounded exosphere. Volatiles include elements that do not interact strongly with the surface, such as neon (detected on the Moon) and helium (detected both on the Moon and at Mercury), but also argon, a noble gas (detected on the Moon) that surprisingly adsorbs at the cold lunar nighttime surface. Refractories include species such as calcium, magnesium, iron, and aluminum, all of which have very strong bonds with the lunar surface and thus need energetic processes to be ejected into the exosphere. Here we focus on the properties of species that have been detected in the exospheres of inner Solar System bodies, specifically the Moon and Mercury, and how they provide important information to understand source and loss processes of these exospheres, as well as their dependence on variations in external drivers.

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The Boundary of Alkali Surface Boundary Exospheres of Mercury and the Moon

Cited by 20 publications

References 30 publications

Comparative Na and K Mercury and Moon Exospheres

Comparative Na and K Mercury and Moon Exospheres

Selenographic and Local Time Dependence of Lunar Exospheric Sodium as Observed by LADEE

Volatiles and Refractories in Surface-Bounded Exospheres in the Inner Solar System

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