Surface-bounded atmosphere of Europa

Shematovich, V. I.; Johnson, R. E.; Cooper, J. F.; Wong, M. C.

doi:10.1016/j.icarus.2004.08.013

Cited by 113 publications

(161 citation statements)

References 66 publications

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“…The maximum electron density of ~10 4 cm -3 was observed over the trailing hemisphere. The measured scale height, 240 ± 40 km for alititudes less than 300 km, and 440 ± 60 km for altitudes above 300 km, differed significantly from the 20-km scale height predicted for O 2 (e.g., Shematovich et al, 2005). The nondetection occurred over the downstream hemisphere near the center of the plasma wake.…”

Section: Atmospheric Observationsmentioning

confidence: 64%

“…The production of O 2 is equal to the second term in equation (2), and is roughly half that of H 2 . For the ion flux at Europa, the H 2 O yield is on the order of 10 9 /cm 2 s -1 and, due to the effect of the regolith, the O 2 yield is of the same order of magnitude (Shematovich et al, 2005).…”

Section: Sputtering Yieldsmentioning

confidence: 97%

“…(Cooper et al, 2001;Paranicas et al, 2002). Although this rate is lower than the resurfacing rate induced by meteoroid gardening, sputtering is the principal source of Europa's atmosphere (Shematovich et al, 2005;Smyth and Marconi, 2006).…”

Section: Radiation Environmentmentioning

confidence: 98%

“…Atmospheric sputtering by ion-neutral collisions, and dissociation and ionization of atmospheric molecules by low-energy (thermal) electrons, are important loss processes (Table 1) (Saur et al, 1998;Shematovich et al, 2005;Smyth and Marconi, 2006). This radiation also makes the atmosphere visible by producing the UV emissions from O 2 .…”

Section: Radiation Environmentmentioning

confidence: 99%

“…If this atmosphere was only populated by thermal desorption (i.e., evaporation), it would consist only of trace volatiles that would be rapidly depleted, plus a small subsolar component, <~10 12 H 2 O/cm 2 depending on the ice fraction in the surface (Shematovich et al, 2005;Smyth and Marconi, 2006). However, Europa orbits in a region of the jovian magnetosphere in which the trapped plasma density and temperature are relatively high, and its surface is exposed to the solar EUV flux.…”

Section: Introductionmentioning

confidence: 99%

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Composition and Detection of Europa’s Sputter-induced Atmosphere

Johnson¹,

Burger²,

Cassidy³

et al.

Europa

118

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An intense flux of ions and electrons from the jovian magnetosphere both alters and erodes Europa's surface, producing a tenuous atmosphere. This chapter discusses the physical processes that create and remove the atmosphere, such as ion erosion (sputtering), radiation-induced chemical alteration of the surface (radiolysis), and atmospheric loss processes such as ionization and pickup. Special emphasis is placed on ongoing modeling efforts to connect atmospheric properties to surface composition. Models are at present constrained by a small number of observations, but a future mission to Europa has the potential to detect even trace atmospheric species.

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Section: Atmospheric Observationsmentioning

confidence: 64%

Section: Sputtering Yieldsmentioning

confidence: 97%

Section: Radiation Environmentmentioning

confidence: 98%

Section: Radiation Environmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Composition and Detection of Europa’s Sputter-induced Atmosphere

Johnson¹,

Burger²,

Cassidy³

et al.

Europa

118

View full text Add to dashboard Cite

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Self‐consistent multifluid MHD simulations of Europa's exospheric interaction with Jupiter's magnetosphere

et al. 2015

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The Jovian moon, Europa, hosts a thin neutral gas atmosphere, which is tightly coupled to Jupiter's magnetosphere. Magnetospheric ions impacting the surface sputter off neutral atoms, which, upon ionization, carry currents that modify the magnetic field around the moon. The magnetic field in the plasma is also affected by Europa's induced magnetic field. In this paper we investigate the environment of Europa using our multifluid MHD model and focus on the effects introduced by both the magnetospheric and the pickup ion populations. The model self‐consistently derives the electron temperature that governs the electron impact ionization process, which is the major source of ionization in this environment. The resulting magnetic field is compared to measurements performed by the Galileo magnetometer, the bulk properties of the modeled thermal plasma population is compared to the Galileo Plasma Subsystem observations, and the modeled surface precipitation fluxes are compared to Galileo Ultraviolet Spectrometer observations. The model shows good agreement with the measured magnetic field and reproduces the basic features of the plasma interaction observed at the moon for both the E4 and the E26 flybys of the Galileo spacecraft. The simulation also produces perturbations asymmetric about the flow direction that account for observed asymmetries.

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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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Surface-bounded atmosphere of Europa

Cited by 113 publications

References 66 publications

Composition and Detection of Europa’s Sputter-induced Atmosphere

Composition and Detection of Europa’s Sputter-induced Atmosphere

Self‐consistent multifluid MHD simulations of Europa's exospheric interaction with Jupiter's magnetosphere

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

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