Constraining Europa's Subsolar Atmosphere With a Joint Analysis of HST Spectral Images and Galileo Magnetic Field Data

Villa, J. S. Cervantes; Saur, Joachim

doi:10.1029/2022ja030472

Cited by 7 publications

(21 citation statements)

References 57 publications

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“…Nevertheless, a localized, persistent H 2 O exosphere has recently been detected by HST above Europa's subsolar point, which at the time of observation was located in the moon's orbital trailing hemisphere (Roth, 2021). Evidence for this local H 2 O exosphere was also found in Galileo magnetometer data from the E12 flyby (Cervantes & Saur, 2022). Neutral oxygen largely remains bound by Europa's gravity, and does not efficiently stick to the surface ice upon re‐impacting (Eviatar et al., 1985), residing in the exosphere on timescales of tens of hours (Smyth & Marconi, 2006).…”

Section: Introductionsupporting

confidence: 61%

“…Laboratory data on electron impact ionization frequencies of H 2 O is not available in the peer‐reviewed literature. Therefore, Cervantes and Saur (2022) utilized the same electron impact ionization frequencies for H 2 O as for O 2 , similar to Arnold et al. (2019).…”

Section: Modeling Energetic Electron Influx Onto Europamentioning

confidence: 99%

“…Using an MHD model, Cervantes and Saur (2022) recently investigated the influence of an additional H 2 O exosphere above Europa's upstream apex, as identified by Roth (2021), on the local electromagnetic field structure during the Galileo E12 flyby. By including such a localized H 2 O exosphere they were able to explain several fine structures in the magnetometer data from this flyby which could not be reproduced with their radially symmetric, barometric O 2 exosphere (see Figure 10 from that paper).…”

Section: Modeling Energetic Electron Influx Onto Europamentioning

confidence: 99%

“…During the E12 Galileo flyby, Europa's subsolar and sub‐plasma points were indeed co‐located. Therefore, the study of Cervantes and Saur (2022) could not provide any additional insights into the local time dependence of the H 2 O exospheric density bulge. In other words, it is currently not feasible to include the proper location of such an H 2 O density enhancement as we model Europa's plasma interaction over the course of a synodic rotation.…”

Section: Modeling Energetic Electron Influx Onto Europamentioning

confidence: 99%

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Surface‐Plasma Interactions at Europa in Draped Magnetospheric Fields: The Contribution of Energetic Electrons to Energy Deposition and Sputtering

Addison,

Liuzzo,

Simon

2023

JGR Space Physics

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We calculate the time‐varying spatial distribution of energetic magnetospheric electron influx onto Europa’s surface by combining a hybrid model of the moon’s draped electromagnetic environment with a relativistic particle tracer. We generate maps of the energetic electron influx patterns at four distinct locations of Europa relative to the center of the Jovian magnetospheric current sheet. For a full synodic rotation of Jupiter, these results are applied to constrain the averaged number and energy influx patterns as well as the O2 sputtering rates associated with energetic electron precipitation. We also determine the relative contributions of magnetospheric ions and electrons to surface erosion and exospheric genesis at Europa. Our major results are: (a) Except for a small region near Europa’s downstream apex, the moon’s entire surface is exposed to heavy irradiation by magnetospheric electrons. (b) The spatial distribution of energetic electron influx onto Europa’s surface is only slightly modified by field line draping and the induced magnetic field from the moon’s subsurface ocean. (c) The contributions of magnetospheric electron and ion impacts to energy deposition onto Europa’s surface are of the same order of magnitude. (d) Within uncertainties, impinging magnetospheric electrons and ions make similar contributions to O2 sputtering from Europa’s surface. (e) The spatial distribution of electron energy influx and the observed concentrations of sulfuric acid (H2SO4) are only weakly correlated, suggesting that energy deposition by magnetospheric electron impacts is not a necessary agent for H2SO4 production within Europa’s surface.This article is protected by copyright. All rights reserved.

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Section: Introductionsupporting

confidence: 61%

Section: Modeling Energetic Electron Influx Onto Europamentioning

confidence: 99%

Section: Modeling Energetic Electron Influx Onto Europamentioning

confidence: 99%

Section: Modeling Energetic Electron Influx Onto Europamentioning

confidence: 99%

See 2 more Smart Citations

Surface‐Plasma Interactions at Europa in Draped Magnetospheric Fields: The Contribution of Energetic Electrons to Energy Deposition and Sputtering

Addison,

Liuzzo,

Simon

2023

JGR Space Physics

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“…(2019); Harris et al. (2021); Cervantes and Saur (2022). However, none of them have a perfect fit to all the flybys.…”

Section: Resultsmentioning

confidence: 99%

Europa's Perturbed Fields and Induced Dipole Affect Energetic Proton Depletions During Distant Alfvén Wing Flybys

et al. 2023

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We investigate the causes of energetic proton (80‐540 keV) depletions measured during the two most distant flybys of Europa by Galileo, E17 and E25A, which encountered the Alfvén wings. First, by simulating the proton flux with a Monte Carlo particle tracing code we investigate the effect of: electromagnetic field perturbations, the induced dipole, atmospheric charge exchange and plumes. Inhomogeneous fields associated with the Alfvén wings and the ionosphere strongly affect the depletions. For homogeneous fields the depletion along the trajectory is focused on a narrow pitch angle range and has no structure, whereas the depletion for perturbed (inhomogeneous) fields represents a wider and complex structure. Furthermore, also the induced dipole alters the depletion structure. The effect of plumes (density 2.5 × 1015m−3) and charge exchange on the proton depletion is minor. Secondly, we compare the simulations to the proton measurements. The simulations with inhomogeneous fields describe the data qualitatively better than the homogeneous case, suggesting that indeed field perturbations are responsible for the measured losses. We attribute discrepancies between the simulations and the proton measurements to discrepancies between the simulated and real fields. We argue that simulating the fields along the trajectory is a good first step, but that ideally the energetic ion flux is reconstructed well to gain confidence in the interpretation of the simulated magnetic field. In conclusion, energetic ion observations along distant flybys through the Alfvén wings are suitable for isolating the characteristics of the global configuration of the magnetospheric interaction region of Europa (or other moons).

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Magnetic Signatures of the Interaction Between Europa and Jupiter's Magnetosphere During the Juno Flyby

Addison,

Haynes,

Stahl

et al. 2024

Geophysical Research Letters

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Based on a hybrid model of Europa's magnetospheric interaction, we provide context for the magnetic field perturbations observed by the Juno spacecraft during its only close flyby of the moon in September 2022. By systematically varying the incident flow conditions and the density profile of Europa's atmosphere, we demonstrate that the observed, large‐scale signatures of magnetic field draping are consistent with a dawn‐dusk asymmetry in the moon's neutral envelope. During the flyby, such an asymmetry would have enhanced the magnetic perturbations in Europa's anti‐Jovian hemisphere, explaining why the spacecraft already detected strong field line draping while still several moon radii away. Conversely, a reduced neutral density in the sub‐Jovian hemisphere can explain why the perturbations in the flow‐aligned field component remained nearly constant as Juno approached Europa. While a dawn‐dusk asymmetry in Europa's atmosphere has been predicted by theoretical work, our results provide the first in situ hints of its presence.

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Constraining Europa's Subsolar Atmosphere With a Joint Analysis of HST Spectral Images and Galileo Magnetic Field Data

Cited by 7 publications

References 57 publications

Surface‐Plasma Interactions at Europa in Draped Magnetospheric Fields: The Contribution of Energetic Electrons to Energy Deposition and Sputtering

Surface‐Plasma Interactions at Europa in Draped Magnetospheric Fields: The Contribution of Energetic Electrons to Energy Deposition and Sputtering

Europa's Perturbed Fields and Induced Dipole Affect Energetic Proton Depletions During Distant Alfvén Wing Flybys

Magnetic Signatures of the Interaction Between Europa and Jupiter's Magnetosphere During the Juno Flyby

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