Potassium in Europa's Atmosphere

Brown, Michael E.

doi:10.1006/icar.2001.6612

Cited by 96 publications

(119 citation statements)

References 19 publications

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“…Beyond 2 R E , few measurements of the Na and K exospheric densities should provide crucial information on their relative abundances below the radiation's penetration depth . Good agreement with Brown [2001] observations is obtained by adjusting the average surface source rates of potassium and sodium. Using the average sodium source rate of 3 Â 10 6 cm…”

Section: Model's Descriptionsupporting

confidence: 60%

“…[5] Brown [2001] observations of the Na/K exospheric ratio (hereafter noted F E ) were carried out with a slit parallel to the rotational pole of Jupiter and placed at various distances from Europa's center along an east/west axis. Variations of the average simulated ratio of the line of sight column densities of Na and K along an east/west axis and as a function of the distance from Europa's surface are shown in Figure 1 (red line).…”

Section: Model's Descriptionmentioning

confidence: 99%

“…[2] Brown [2001] observed simultaneously sodium and potassium at Io and Europa using the HIRES Echelle spectrograph at the Keck telescope. He derived a Na/K line-of-sight density ratio close to 25 at radial distances between 5 and 15 Europa radii (R E ) from Europa center and a ratio close to 10 from 10 to 20 Io radii from Io center.…”

Section: Introductionmentioning

confidence: 99%

“…This model accounts for non-uniform sources of alkalis at Europa's surface and allows us to describe the relation between exospheric and surface densities of the ejected material. In the present paper, the exospheres of sodium and potassium are built and compared to observations by Brown [2001] in order to better constrain the Na/K source rates ratio F S at the surface and to analyze possible signatures of the Na/K surface distribution in Europa's exosphere.…”

Section: Introductionmentioning

confidence: 99%

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Exospheric signatures of alkali abundances in Europa's regolith

Cipriani¹,

Leblanc²,

Witasse³

et al. 2009

Geophysical Research Letters

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International audienceThe sodium and potassium exospheres of Europa are described as well as the variations of the Na/K ratio from Europa's surface up to about 20 Europa radii. Observations carried out by M. E. Brown (2001) are used to constrain the Na and K source terms. We find that an average source rates ratio of 17 ± 2 at the surface and loss rates ratio of 26 ± 2 reproduce well the observations. These values are consistent with the conclusions by R. E. Johnson et al. (2002) on its most probable origin. Moreover, we here show that a local increase of the surface Na/K ratio by a factor 2 in a 20° × 30° wide region should induce an observable exospheric signature between 80 and 300 km above the surface. Therefore simultaneous observations of sodium and potassium from an Europa orbiter would allow one to derive important properties of the surface and subsurface of the Galilean moon

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Section: Model's Descriptionsupporting

confidence: 60%

Section: Model's Descriptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Exospheric signatures of alkali abundances in Europa's regolith

Cipriani¹,

Leblanc²,

Witasse³

et al. 2009

Geophysical Research Letters

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“…First, we decrease the potassium concentration to set the oceanic Na/K atomic ratio to 25 to match the value observed in the atmosphere of Europa [Brown, 2001]. Second, thermodynamic calculations of aqueous chemistry, which bMg is adjusted to achieve charge balance for the Kla model.…”

Section: A Working Model For Oceanic Chemistry To Get a Working Chemmentioning

confidence: 99%

Composition and stability of salts on the surface of Europa and their oceanic origin

2001

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Abstract. We present theoretical models of the composition, the relative abundances, and the stability of hydrated salts on the surface and in the icy shell of Jupiter's satellite Europa and discuss whether those salts have an oceanic origin. The evaluations were done with thermodynamic calculations of (1) salt dehydration equilibria at the conditions of the surface of Europa and its icy shell, (2) chemical equilibria involving solids and water vapor in the Na-K-Mg-Ca-S-C1-H20 system at surface temperatures and variable partial pressures of water vapor, and (3) changes in aquatic chemistry and sequences of salt precipitation from freezing oceanic water, using cosmochemical, mass balance, and physical-chemical constraints on the elemental and ionic composition of the ocean. Mass balance calculations of total or partial extraction of elements into an ocean from a carbonaceous chonddhte type mantle show that magnesium and sulfate rather than chloride and sodium could be the most abundant solutes in the ocean. Freezing oceanic water of this composition leads to brines that differ in composition from the original water and to deposition of ice and highly hydrated sulfates of Mg, Na, and Ca as well as alkali chlorides. After freezing is complete, highly hydrated salts remain stable in ice-bearing surface matedhals and throughout the icy shell. For hypothetical surface salt lag deposits, formed through sublimation/sputtedhng of ice and dehydration of salts, we predict hydration stratification with depth, approaching the highest hydration states in ice-beadhng matedhals in the lowest parts of the deposits. We discuss the effects of fast disequilibrium freezing and variable dehydration rates of salts on the predicted mineral assemblages at the surface. All of our models, which are independent of observations, predict the predominance of Mg and Na sulfates in surface salts, in agreement with spectroscopic models for the nonicy surface matedhal in the near infrared spectral region. IntroductionGalileo spacecraft reflectance spectroscopy in the near-infrared spectral region tentatively indicates the presence of hydrated saks in a non-H20 ice component on the surface of Jupiter's moon Europa [McCord et al., 1998a[McCord et al., , 1998b[McCord et al., , 1999. It was shown that magnesium and sodium sulfates (MgSO4.7H20, epsomite; MgSO4.Na2SO4.4H20, bloedite; Na2SO4.10H20, mirabilite), sodium carbonate (Na2CO3.10H20, natron), and mixtures of these salts provide good fits for the near-infrared spectra for the nonicy material Here we undertake evaluations of this type from a theoretical basis. In this paper we present internally consistent geochemical and thermodynamic models that describe leaching of aqueous components from a silicate mantle, aquatic chemistry of the ocean, freezing of oceanic water during upwelling in fractures in the icy crust and on the surface, and dehydration of salts on the surface of Europa. The results are compared with observational models for the composition and distribution of the nonicy surface mater...

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Europa's far ultraviolet oxygen aurora from a comprehensive set of HST observations

et al. 2016

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We analyze a large set of far ultraviolet oxygen aurora images of Europa's atmosphere taken by Hubble's Space Telescope Imaging Spectrograph (HST/STIS) in 1999 and on 19 occasions between 2012 and 2015. We find that both brightness and aurora morphology undergo systematic variations correlated to the periodically changing plasma environment. The time variable morphology seems to be strongly affected by Europa's interaction with the magnetospheric plasma. The brightest emissions are often found in the polar region where the ambient Jovian magnetic field line is normal to Europa's disk. Near the equator, where bright spots are found at Io, Europa's aurora is faint suggesting a general difference in how the plasma interaction shapes the aurora at Io and Europa. The dusk side is consistently brighter than the dawnside with only few exceptions, which cannot be readily explained by obvious plasma physical or known atmospheric effects. Brightness ratios of the near‐surface OI] 1356 Å to OI 1304 Å emissions between 1.5 and 2.8 with a mean ratio of 2.0 are measured, confirming that Europa's bound atmosphere is dominated by O2. The 1356/1304 ratio decreases with increasing altitude in agreement with a more extended atomic O corona, but O2 prevails at least up to altitudes of ∼900 km. Differing 1356/1304 line ratios on the plasma upstream and downstream hemispheres are explained by a differing O mixing ratio in the near‐surface O2 atmosphere of ∼5% (upstream) and ≲1% (downstream), respectively. During several eclipse observations, the aurora does not reveal any signs of systematic changes compared to the sunlit images suggesting no or only weak influence of sunlight on the aurora and an optically thin atmosphere.

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Potassium in Europa's Atmosphere

Cited by 96 publications

References 19 publications

Exospheric signatures of alkali abundances in Europa's regolith

Exospheric signatures of alkali abundances in Europa's regolith

Composition and stability of salts on the surface of Europa and their oceanic origin

Europa's far ultraviolet oxygen aurora from a comprehensive set of HST observations

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