Source rates and ion recycling rates for Na and K in Mercury's atmosphere

Killen, R. M.; Sarantos, M.; Potter, A. E.; Reiff, P. H.

doi:10.1016/j.icarus.2004.04.007

Cited by 93 publications

(101 citation statements)

References 45 publications

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“…Charged particle and photon sputtering work on the first few monolayers of the surface grains, so pre-sputtered atoms must first make their way to the monolayers by diffusion. Gardening rates for the crust are much faster than the time required to deplete a grain of a given species, providing a constant supply of neutrals to the exosphere (Killen et al, 2004). Based upon the Mariner 10 observations, the magnetospheric reconfiguratim time is only a few minutes Slavin and Holzer, 1979a;Luhmann et al, 1998).…”

Section: Magnetosphere?mentioning

confidence: 99%

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MESSENGER: Exploring Mercury’s Magnetosphere

et al. 2007

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Abstract. The MESSENGER mission to Mercury offers our first opportunity to explore this planet's miniature magnetosphere since the brief flybys of Mariner 10. Mercury's magnetosphere is unique in many respects. The magnetosphere of Mercury is among the smallest in the solar system; its magnetic field typically stands off the solar wind only -1000 to 2000 km above the surface. For this reason there are no closed drift paths for energetic particles and, hence, no radiation belts. The characteristic time scales for wave propagation and convective transport are short and kinetic and fluid modes may be coupled. Magnetic reconnection at the dayside magnetopause may erode the subsolar magnetosphere allowing solar wind ions to impact directly the regolith. Inductive currents in Mercury's interior may act to modify the solar wind interaction by resisting changes due to solar wind pressure variations. Indeed, observations of these induction effects may be an important source of information on the state of Mercury's interior. In addition, Mercury's magnetosphere is the only one with its defining magnetic flux tubes rooted in a planetary regolith as opposed to an atmosphere with a conductive ionospheric layer. This lack of an ionosphere is probably the underlying reason for the brevity of the very intense, but short-lived, -1-2 min, substorm-like energetic particle events observed by Mariner 10 during its first traversal of Mercury's magnetic tail. Because of Mercury's proximity to the sun, 0.3 -0.5 AU, this magnetosphere experiences the most extreme driving forces in the solar system. All of these factors are expected to produce complicated interactions involving the exchange and re-cycling of neutrals and ions between the solar wind, magnetosphere, and regolith. The electrodynamics of Mercury's magnetosphere are expected to be equally complex, with strong forcing by the solar wind, magnetic reconnection at the magnetopause and in the tail, and the pick-up of planetary ions all driving field-aligned electric currents.However, these field-aligned currents do not close in an ionosphere, but in some other manner. In addition to the insights-into magnetospheric physics offered by study of the solar wind -Mercury system, quantitative specification of the "external" magnetic field generated by magnetospheric currents is necessary for accurate determination of the strength and multi-polar decomposition of Mercury's intrinsic magnetic field.MESSENGER'S highly capable instrumentation and broad orbital coverage will greatly advance our understanding of both the origin of Mercury's magnetic field and the acceleration of charged particles in small magnetospheres. In. this article, we review what is known about Mercury's magnetosphere and describe the MESSENGER science team's strategy for obtaining answers to the outstanding science questions surrounding the interaction of the solar wind with Mercury and its small, but dynamic, magnetosphere.2

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Section: Magnetosphere?mentioning

confidence: 99%

“…Recycling rates for these studies were 10-1596. Killen et al (2004) utilized a new model (see Sarantos 2000) that, unlike Delcourt et al (2003), takes into account radial magnetic field orientation. Their ion initial energies were also -1 eV.…”

Section: Magnetosphere?mentioning

confidence: 99%

MESSENGER: Exploring Mercury’s Magnetosphere

et al. 2007

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“…"Self sputtering" is itself an inconsequential source for the exosphere [e.g., 1298 Delcourt et al, Poppe et al, 2013] as the recycled ion fluxes are a small 1299 portion of the inferred neutral efflux (~10 7 Na cm -2 s -1 ). However, recycling could be 1300 important if ions neutralized in the soil increase the available reservoir for trace 1301 species [Killen et al, 2004]. High ion recycling rates will obviously increase the 1302 reservoir for exogenous species of the exosphere that are in balance with the solar 1303 wind influx (e.g., He, Ne); but they could also increase the reservoir for exospheric 1304 Na and K, which are very nearly depleted on the dayside [Leblanc and Johnson, 2003, 1305 to levels that can be supported by grain diffusion [Killen et al, 2004].…”

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confidence: 99%

“…However, recycling could be 1300 important if ions neutralized in the soil increase the available reservoir for trace 1301 species [Killen et al, 2004]. High ion recycling rates will obviously increase the 1302 reservoir for exogenous species of the exosphere that are in balance with the solar 1303 wind influx (e.g., He, Ne); but they could also increase the reservoir for exospheric 1304 Na and K, which are very nearly depleted on the dayside [Leblanc and Johnson, 2003, 1305 to levels that can be supported by grain diffusion [Killen et al, 2004]. Broad 1306 bands of nightside precipitation of Na+ with fluxes ~10 5 Na+ cm -2 s -1 and extending 1307 up to ±50° latitude form when realistic conditions about the surface conductance are 1308 adopted [Seki et al, 2013].…”

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confidence: 99%

Plasma Sources in Planetary Magnetospheres: Mercury

Raines¹,

DiBraccio²,

Cassidy³

et al. 2016

Plasma Sources of Solar System Magnetospheres

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“…In LJ2003, some of the possible exospheric signatures induced by the impoverishment of the dayside surface were Simulated. Killen et al (2004) also calculated how surface depletion might impact the local surface ejection rates. These authors showed, as an example, how the reservoir for thermal desorption (TD) is quickly reduced with increasing local time, so that the TD rate becomes of the same order of magnitude as the photon stimulated desorption (PSD) rate (see Leblanc et al 2007 for further explanations of these processes).…”

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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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Source rates and ion recycling rates for Na and K in Mercury's atmosphere

Cited by 93 publications

References 45 publications

MESSENGER: Exploring Mercury’s Magnetosphere

MESSENGER: Exploring Mercury’s Magnetosphere

Plasma Sources in Planetary Magnetospheres: Mercury

Mercury exosphere I. Global circulation model of its sodium component

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