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Plasma Interactions with Icy Bodies in the Solar System
Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.ORCID iD: 0000-0002-5765-2806
2016 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Plasmaväxelverkan med isiga kroppar i solsystemet (Swedish)
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. , 80 p.
Series
IRF Scientific Report, ISSN 0284-1703 ; 307
Keyword [en]
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: urn:nbn:se:umu:diva-117666ISBN: 978-91-982951-1-5 (print)OAI: oai:DiVA.org:umu-117666DiVA: diva2:925397
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: 2016-09-02Bibliographically approved
List of papers
1. Callisto plasma interactions: Hybrid modeling including induction by a subsurface ocean
Open this publication in new window or tab >>Callisto plasma interactions: Hybrid modeling including induction by a subsurface ocean
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2015 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 6, 4877-4889 p.Article in journal (Refereed) Published
Abstract [en]

By using a hybrid plasma solver (ions as particles and electrons as a fluid), we have modeled the interaction between Callisto and Jupiter's magnetosphere for variable ambient plasma parameters. We compared the results with the magnetometer data from flybys (C3, C9, and C10) by the Galileo spacecraft. Modeling the interaction between Callisto and Jupiter's magnetosphere is important to establish the origin of the magnetic field perturbations observed by Galileo and thought to be related to a subsurface ocean. Using typical upstream magnetospheric plasma parameters and a magnetic dipole corresponding to the inductive response inside the moon, we show that the model results agree well with observations for the C3 and C9 flybys, but agrees poorly with the C10 flyby close to Callisto. The study does support the existence of a subsurface ocean at Callisto.

Keyword
Callisto, plasma interaction, hybrid model, subsurface ocean, Galileo flyby, magnetosphere
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-107178 (URN)10.1002/2015JA021212 (DOI)000358199100059 ()
Available from: 2015-09-01 Created: 2015-08-19 Last updated: 2017-12-04Bibliographically approved
2. 3D-modeling of Callisto's exosphere caused by thermal plasma sputtering
Open this publication in new window or tab >>3D-modeling of Callisto's exosphere caused by thermal plasma sputtering
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(English)In: Journal of Geophysical Research - Planets, ISSN 2169-9097, E-ISSN 2169-9100Article in journal (Other academic) Submitted
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-119795 (URN)
Available from: 2016-04-27 Created: 2016-04-27 Last updated: 2017-11-30
3. Ceres interaction with the solar wind
Open this publication in new window or tab >>Ceres interaction with the solar wind
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2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 5, 2070-2077 p.Article in journal (Refereed) Published
Abstract [en]

The solar wind interaction with Ceres is studied for a high water vapor release from its surface using a hybrid model including photoionization. We use a water vapor production rate of 6 kg/s, thought to be due to subsurface sublimation, corresponding to a detection on 6 March 2013 by the Herschel Space Observatory. We present the general morphology of the plasma interactions, both close to Ceres and on a larger scale. Mass loading of water ions causes a magnetic pileup region in front of Ceres, where the solar wind deflects up to 15 ∘ and slows down by 15%. The global plasma interaction with Ceres is not greatly affected by the source location of water vapor nor on gravity, only on the production rate of water vapor. On a global scale, Ceres has a comet-like interaction with the solar wind with observable perturbations farther than 250 Ceres radii downstream of the body.

National Category
Fusion, Plasma and Space Physics
Research subject
Space and Plasma Physics
Identifiers
urn:nbn:se:umu:diva-119797 (URN)10.1002/2016GL072375 (DOI)000398183700003 ()
Funder
Swedish National Space Board
Available from: 2016-04-27 Created: 2016-04-27 Last updated: 2017-05-12Bibliographically approved
4. Mass-loading of the solar wind at 67P/Churyumov-Gerasimenko: Observations and modelling
Open this publication in new window or tab >>Mass-loading of the solar wind at 67P/Churyumov-Gerasimenko: Observations and modelling
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2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 596, A42Article in journal (Refereed) Published
Abstract [en]

Context. The first long-term in-situ observation of the plasma environment in the vicinity of a comet, as provided by the European Rosetta spacecraft.

Aims. Here we offer characterisation of the solar wind flow near 67P/Churyumov-Gerasimenko (67P) and its long term evolution during low nucleus activity. We also aim to quantify and interpret the deflection and deceleration of the flow expected from ionization of neutral cometary particles within the undisturbed solar wind.

Methods. We have analysed in situ ion and magnetic field data and combined this with hybrid modeling of the interaction between the solar wind and the comet atmosphere.

Results. The solar wind deflection is increasing with decreasing heliocentric distances, and exhibits very little deceleration. This is seen both in observations and in modeled solar wind protons. According to our model, energy and momentum are transferred from the solar wind to the coma in a single region, centered on the nucleus, with a size in the order of 1000 km. This interaction affects, over larger scales, the downstream modeled solar wind flow. The energy gained by the cometary ions is a small fraction of the energy available in the solar wind.

Conclusions. The deflection of the solar wind is the strongest and clearest signature of the mass-loading for a small, low-activity comet, whereas there is little deceleration of the solar wind. 

Place, publisher, year, edition, pages
EDP Sciences, 2016
Keyword
comets: general, comets: individual: 67P/Churyumov-Gerasimenko, plasmas, methods: observational, methods: numerical, space vehicles: instruments
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-119798 (URN)10.1051/0004-6361/201628797 (DOI)000390797900062 ()
Available from: 2016-04-27 Created: 2016-04-27 Last updated: 2017-11-30Bibliographically approved

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