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Three‐Dimensional Modeling of Callisto's Surface Sputtered Exosphere Environment
Physikalisches Institut, University of Bern, Bern.
Institute for Chemical Engineering and Environmental Technology, Graz.
Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna, Sweden.ORCID iD: 0000-0002-5765-2806
Swedish Institute of Space Physics, Kiruna, Sweden.ORCID iD: 0000-0001-5494-5374
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2019 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 8, p. 7157-7169Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2019. Vol. 124, no 8, p. 7157-7169
Keywords [en]
Callisto, atmosphere, exosphere, Jupiter, plasma, sputtering
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:umu:diva-119795DOI: 10.1029/2019JA026610Scopus ID: 2-s2.0-85070838044OAI: oai:DiVA.org:umu-119795DiVA, id: diva2:923874
Note

Originally included in thesis in manuscript form with title "3D-modeling of Callisto's exosphere caused by thermal plasma sputtering" by the authors Pfleger, Martin; Lindkvist, Jesper; Vorburger, Audrey; Holmström, Mats; Lichtenegger, Herbert I. M.; Lammer, Helmut; Wurz, Peter; Barabash, Stas.

Available from: 2016-04-27 Created: 2016-04-27 Last updated: 2019-10-03Bibliographically approved
In thesis
1. Plasma Interactions with Icy Bodies in the Solar System
Open this publication in new window or tab >>Plasma Interactions with Icy Bodies in the Solar System
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Plasmaväxelverkan med isiga kroppar i solsystemet
Abstract [en]

Here I study the “plasma interactions with icy bodies in the solar system”, that is, my quest to understand the fundamental processes that govern such interactions. By using numerical modelling combined with in situ observations, one can infer the internal structure of icy bodies and their plasma environments.

After a broad overview of the laws governing space plasmas a more detailed part follows. This contains the method on how to model the interaction between space plasmas and icy bodies. Numerical modelling of space plasmas is applied to the icy bodies Callisto (a satellite of Jupiter), the dwarf planet Ceres (located in the asteroid main belt) and the comet 67P/Churyumov-Gerasimenko.

The time-varying magnetic field of Jupiter induces currents inside the electrically conducting moon Callisto. These create magnetic field perturbations thought to be related to conducting subsurface oceans. The flow of plasma in the vicinity of Callisto is greatly affected by these magnetic field perturbations. By using a hybrid plasma solver, the interaction has been modelled when including magnetic induction and agrees well with magnetometer data from flybys (C3 and C9) made by the Galileo spacecraft. The magnetic field configuration allows an inflow of ions onto Callisto’s surface in the central wake. Plasma that hits the surface knocks away matter (sputtering) and creates Callisto’s tenuous atmosphere.

A long term study of solar wind protons as seen by the Rosetta spacecraft was conducted as the comet 67P/Churyumov-Gerasimenko approached the Sun. Here, extreme ultraviolet radiation from the Sun ionizes the neutral water of the comet’s coma. Newly produced water ions get picked up by the solar wind flow, and forces the solar wind protons to deflect due to conservation of momentum. This effect of mass-loading increases steadily as the comet draws closer to the Sun. The solar wind is deflected, but does not lose much energy. Hybrid modelling of the solar wind interaction with the coma agrees with the observations; the force acting to deflect the bulk of the solar wind plasma is greater than the force acting to slow it down.

Ceres can have high outgassing of water vapour, according to observations by the Herschel Space Observatory in 2012 and 2013. There, two regions were identified as sources of water vapour. As Ceres rotates, so will the source regions. The plasma interaction close to Ceres depends greatly on the source location of water vapour, whereas far from Ceres it does not. On a global scale, Ceres has a comet-like interaction with the solar wind, where the solar wind is perturbed far downstream of Ceres.

Abstract [sv]

Här studerar jag “plasmaväxelverkan med isiga kroppar i solsystemet”, det vill säga, min strävan är att förstå de grundläggande processerna som styr sådana interaktioner. Genom att använda numerisk modellering i kombination med observationer på plats vid himlakropparna kan man förstå sig på deras interna strukturer och rymdmiljöer.

Efter en bred översikt över de fysiska lagar som styr ett rymdplasma följer en mer detaljerad del. Denna innehåller metoder för hur man kan modellera växelverkan mellan rymdplasma och isiga kroppar. Numerisk modellering av rymdplasma appliceras på de isiga himlakropparna Callisto (en måne kring Jupiter), dvärgplaneten Ceres (lokaliserad i asteroidbältet mellan Mars och Jupiter) och kometen 67P/Churyumov-Gerasimenko.

Det tidsvarierande magnetiska fältet kring Jupiter inducerar strömmar inuti den elektriskt ledande månen Callisto. Dessa strömmar skapar magnetfältsstörningar som tros vara relaterade till ett elektriskt ledande hav under Callistos yta. Plasmaflödet i närheten av Callisto påverkas i hög grad av dessa magnetfältsstörningar. Genom att använda en hybrid-plasma-lösare har växelverkan modellerats, där effekten av magnetisk induktion har inkluderats. Resultaten stämmer väl överens med magnetfältsdata från förbiflygningarna av Callisto (C3 och C9) som gjordes av den obemannade rymdfarkosten Galileo i dess bana kring Jupiter. Den magnetiska konfigurationen som uppstår möjliggör ett inflöde av laddade joner på Callistos baksida. Plasma som träffar ytan slår bort materia och skapar Callistos tunna atmosfär.

En långtidsstudie av solvindsprotoner sett från rymdfarkosten Rosetta utfördes då kometen 67P/Churyumov-Gerasimenko närmade sig solen. Ultraviolett strålning från solen joniserar det neutrala vattnet i kometens koma (kometens atmosfär). Nyligt joniserade vattenmolekyler plockas upp av solvindsflödet och tvingar solvindsprotonernas banor att böjas av, så att rörelsemängden bevaras. Denna effekt ökar stadigt då kometen närmar sig solen. Solvinden böjs av kraftigt, men förlorar inte mycket energi. Hybridmodellering av solvindens växelverkan bekräftar att kraften som verkar på solvinden till störst del får den att böjas av, medan kraften som verkar till att sänka dess fart är mycket lägre.

Ceres har enligt observationer av rymdteleskopet Herschel under 2012 och 2013 haft högt utflöde av vattenånga från dess yta. Där har två regioner identifierats som källor för vattenångan. Eftersom Ceres roterar kommer källornas regioner göra det också. Plasmaväxelverkan i närheten av Ceres beror i hög grad på vattenångskällans placeringen, medan det inte gör det långt ifrån Ceres. På global nivå har Ceres en kometliknande växelverkan med solvinden, där störningar i solvinden propagerar långt nedströms från Ceres.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2016. p. 80
Series
IRF Scientific Report, ISSN 0284-1703 ; 307
Keywords
plasma interactions, icy bodies, solar system, space physics, plasma physics, hybrid model, numerical model, solar wind, magnetosphere, sub-Alfvénic, subsonic, non-collisional, atmosphereless, exosphere, coma, subsurface ocean, induction, magnetic dipole, pick-up ion, mass-loading, moon, natural satellite, dwarf planet, comet, Jupiter, Jovian, Callisto, Ceres, 67P, Churyumov-Gerasimenko
National Category
Fusion, Plasma and Space Physics
Research subject
Space and Plasma Physics
Identifiers
urn:nbn:se:umu:diva-117666 (URN)978-91-982951-1-5 (ISBN)
External cooperation:
Public defence
2016-05-31, Aulan, Rymdcampus 1, Kiruna, 09:00 (English)
Opponent
Supervisors
Funder
Swedish National Space BoardThe Royal Swedish Academy of Sciences
Available from: 2016-05-10 Created: 2016-03-03 Last updated: 2018-06-07Bibliographically approved

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