| 1. |
- Biber, Herbert, et al.
(författare)
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Solar wind Helium ion interaction with Mg and Fe rich pyroxene as Mercury surface analogue
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : ELSEVIER. - 0168-583X .- 1872-9584. ; 480, s. 10-15
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Tidskriftsartikel (refereegranskat)abstract
- The surface of Mercury is continuously exposed to impinging solar wind ions. To improve the understanding of space weathering and exosphere formation, a detailed investigation of the ion-surface interaction is necessary. Magnesium and iron rich pyroxene (Ca,Mg,Fe)(2)[Si2O6] samples were used as analogues for Mercury's surface and irradiated with He+ ions at solar wind energies of 4 keV. Several regimes of implantation and sputtering were observed there. The total estimated mass of implanted He coincides with the mass decrease due to He outgassing during subsequent Thermal Desorption Spectroscopy measurements. Comparison to established modeling efforts and SDTrimSP simulations show that a He saturation concentration of 10 at.% has to be assumed. A complete removal of He is observed by heating to 530 K. On the surface of Mercury, temperatures between about 100 K and 700 K are expected. This temperature will therefore influence the implantation and release of He into Mercury's exosphere.
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| 2. |
- Galli, André, et al.
(författare)
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The tailward flow of energetic neutral atoms observed at Mars
- 2008
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Ingår i: Journal of Geophysical Research. - Washington : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 113
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Tidskriftsartikel (refereegranskat)abstract
- The ASPERA-3 experiment on Mars Express provides the first measurements of energetic neutral atoms (ENAs) from Mars. These measurements are used to study the global structure of the interaction of the solar wind with the Martian atmosphere. In this study we describe the tailward ENA flow observed at the nightside of Mars. After characterizing energy spectra of hydrogen ENA signals, we present composite images of the ENA intensities and compare them to theoretical predictions (empirical and MHD models). We find that the tailward flow of hydrogen ENAs is mainly generated by shocked solar wind protons. Despite intensive search, no oxygen ENAs above the instrument threshold are detected. The results challenge existing plasma models and constrain the hydrogen exospheric densities and atmospheric hydrogen and oxygen loss rates at low solar activity.
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| 3. |
- Mogan, Shane R. Carberry R., et al.
(författare)
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Callisto's Atmosphere : First Evidence for H-2 and Constraints on H2O
- 2022
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Ingår i: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 127:11
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Tidskriftsartikel (refereegranskat)abstract
- We explore the parameter space for the contribution to Callisto's H corona observed by the Hubble Space Telescope from sublimated H2O and radiolytically produced H-2 using the Direct Simulation Monte Carlo method. The spatial morphology of this corona produced via photoelectron and magnetospheric electron-impact-induced dissociation is described by tracking the motion of and simulating collisions between the hot H atoms and thermal molecules including a near-surface O-2 component. Our results indicate that sublimated H2O produced from the surface ice, whether assumed to be intimately mixed with or distinctly segregated from the dark nonice or ice-poor regolith, cannot explain the observed structure of the H corona. On the other hand, a global H-2 component can reproduce the observation, and is also capable of producing the enhanced electron densities observed at high altitudes by Galileo's plasma-wave instrument, providing the first evidence of H-2 in Callisto's atmosphere. The range of H-2 surface densities explored, under a variety of conditions, that are consistent with these observations is similar to(0.4-1) x 10(8) cm(-3). The simulated H-2 escape rates and estimated lifetimes suggest that Callisto has a neutral H-2 torus. We also place a rough upper limit on the peak H2O number density (less than or similar to 10(8) cm(-3)), column density (less than or similar to 10(15) cm(-2)), and sublimation flux (less than or similar to 10(12) cm(-2) s(-1)), all of which are 1-2 orders of magnitude less than that assumed in previous models. Finally, we discuss the implications of these results, as well as how they compare to Europa and Ganymede.
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| 4. |
- Szabo, Paul S., et al.
(författare)
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Dynamic Potential Sputtering of Lunar Analog Material by Solar Wind Ions
- 2020
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Ingår i: Astrophysical Journal. - : IOP PUBLISHING LTD. - 0004-637X .- 1538-4357. ; 891:1
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Tidskriftsartikel (refereegranskat)abstract
- Pyroxenes ((Ca, Mg, Fe, Mn)(2)Si2O6) belong to the most abundant rock forming minerals that make up the surface of rocky planets and moons. Therefore, sputtering of pyroxenes by solar wind ions has to be considered as a very important process for modifying the surface of planetary bodies. This is increased due to potential sputtering by multiply charged ions; to quantify this effect, sputtering of wollastonite (CaSiO3) by He2+ ions was investigated. Thin films of CaSiO3 deposited on a quartz crystal microbalance were irradiated, allowing precise, in situ, real time sputtering yield measurements. Experimental results were compared with SDTrimSP simulations, which were improved by adapting the used input parameters. On freshly prepared surfaces, He2+ ions show a significant increase in sputtering, as compared to equally fast He+ ions. However, the yield decreases exponentially with fluence, reaching a lower steady state after sputtering of the first few monolayers. Experiments using Ar8+ ions show a similar behavior, which is qualitatively explained by a preferential depletion of surface oxygen due to potential sputtering. A corresponding quantitative model is applied, and the observed potential sputtering behaviors of both He and Ar are reproduced very well. The results of these calculations support the assumption that mainly O atoms are affected by potential sputtering. Based on our findings, we discuss the importance of potential sputtering for the solar wind eroding the lunar surface. Estimated concentration changes and sputtering yields are both in line with previous modeling for other materials, allowing a consistent perspective on the effects of solar wind potential sputtering.
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| 5. |
- Vorburger, Audrey, et al.
(författare)
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3D Monte-Carlo simulation of Ganymede's atmosphere
- 2024
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 409
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Tidskriftsartikel (refereegranskat)abstract
- We present new model results for H2O, O2, H2, O, and H in the atmosphere of Ganymede. The results are obtained from a collision-less 3D Monte-Carlo model that includes sublimation, ion and electron sputtering, and ion and electron radiolysis. Because Ganymede has its own magnetic field, its immediate plasma environment is particularly complex. The interaction between Ganymede's and Jupiter's magnetospheres makes it highly variable in both space and time. The recent Juno Ganymede flyby provided us with new data on the electron local environment. Based on the electron measurements recorded by the Jovian Auroral Distributions Experiment (JADE), we implement two electron populations, one for the moon's polar regions and one for the moon's auroral regions. Comparing the atmospheric contribution of these newly defined electron populations to the overall source and loss processes is one of the main goals of this work. Our analysis shows that for H2O, sublimation remains the most important source process even after accounting for the new electron populations, delivering more than three orders of magnitude more H2O molecules to the atmosphere than all other source processes combined. The source fluxes for O2 and H2, on the other hand, are dominated by radiolysis induced by the auroral electrons, assuming that the electron fluxes JADE measured during Juno's transit of Ganymede's magnetopause current layer are representative of auroral electrons. Atomic O and H are mainly added to the atmosphere through the dissociation of O2 and H2, which is primarily induced by auroral electrons. Our understanding of Ganymede's atmosphere today is mainly based on spectroscopic observations. The interpretation of spectroscopic data strongly depends on assumptions taken, though. Our analysis shows that for a holistic understanding of Ganymede's atmosphere, simultaneous observations of the moon's surface, atmosphere, and full plasma environment (thermal and energetic ions and electrons) at different times and locations (both with respect to Ganymede and with respect to Jupiter) are particularly important. Such measurements are planned by ESA's Jupiter ICy moons Explorer (JUICE), in particular by the Particle Environment Package (PEP), which will greatly advance our understanding of Ganymede and its atmosphere and plasma environment.
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| 6. |
- Vorburger, Audrey, et al.
(författare)
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3D Monte-Carlo simulation of Ganymede's water exosphere
- 2022
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Ingår i: Icarus. - : Academia Press. - 0019-1035 .- 1090-2643. ; 375
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present ab initio 3D Monte-Carlo simulations of Ganymede's surface sputtered and sublimated H2O exosphere. As inputs, we include surface water content maps and temperature distribution maps based on Galileo and Very Large Telescope (VLT) observations. For plasma precipitation, we use hybrid model results for thermal H+ and O+, energetic H+, O++, S+++, and electrons, with unprecedented energy resolution. Our results show that up to a solar zenith angle of ∼60° and up to ∼600 km altitude, sublimated H2O dominates the atmosphere by up to four orders of magnitudes in number density, while sputtering dominates elsewhere. Sputtering is mainly induced by the impinging O+, O++, and S+++ ions, while protons (H+) and electrons only add about 1% of the total sputtered H2O molecules to the atmosphere. Electrons are thus not important for the generation of the atmosphere, but they are important for spectroscopic observability of the atmosphere since they are the main inducer of the Lyman-α and O I emission lines. The extended H2O atmosphere at altitudes ≳1 Ganymede radius is mainly the result of sputtering by thermal O+ ions, which is the only ion species with substantial fluxes in the low-energy range (10 eV–10 keV), i.e., is the only species that efficiently induces nuclear sputtering. Most released H2O molecules return to the surface where they immediately adsorb, not forming a thermalized atmosphere. The morphology of Ganymede's magnetosphere, and the resulting dichotomies in the surface fluxes of the precipitating magnetospheric particles (polar fluxes > equatorial fluxes and leading equatorial fluxes > trailing equatorial fluxes), are thus well discernible in the sputtered atmosphere, persisting up to altitudes of a few thousand kilometers. In-situ measurements, as they are planned for the upcoming JUpiter ICy Moons Explorer (JUICE) mission, will mainly probe this sputtered atmosphere, except for encounters with the near-surface atmosphere on Ganymede's day-side, where the sublimated atmosphere will be probed instead. Finally, we compare our model results to the first observational evidence for a sublimated H2O atmosphere on Ganymede, and find a very good agreement.
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| 7. |
- Vorburger, Audrey, et al.
(författare)
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Three‐Dimensional Modeling of Callisto's Surface Sputtered Exosphere Environment
- 2019
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 124:8, s. 7157-7169
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Tidskriftsartikel (refereegranskat)abstract
- We study the release of various elements from Callisto's surface into its exosphere by plasma sputtering. The cold Jovian plasma is simulated with a 3‐D plasma‐planetary interaction hybrid model, which produces 2‐D surface precipitation maps for magnetospheric H+, O+, O++, and S++. For the hot Jovian plasma, we assume isotropic precipitation onto the complete spherical surface. Two scenarios are investigated: one where no ionospheric shielding takes place and accordingly full plasma penetration is implemented (no‐ionosphere scenario) and one where an ionosphere lets virtually none of the cold plasma but all of the hot plasma reach Callisto's surface (ionosphere scenario). In the 3‐D exosphere model, neutral particles are sputtered from the surface and followed on their individual trajectories. The 3‐D density profiles show that whereas in the no‐ionosphere scenario the ram direction is favored, the ionosphere scenario produces almost uniform density profiles. In addition, the density profiles in the ionosphere scenario are reduced by a factor of ∼2.5 with respect to the no‐ionosphere scenario. We find that the Neutral Gas and Ion Mass Spectrometer, which is part of the Particle Environment Package on board the JUpiter ICy moons Explorer mission, will be able to detect the different sputter populations from Callisto's icy surface and the major sputter populations from Callisto's nonicy surface. The chemical composition of Callisto's exosphere can be directly linked to the chemical composition of its surface and will offer us information not only on Callisto's formation scenario but also on the building blocks of the Jupiter system.
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