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  • 1.
    Behar, Etienne
    et al.
    Swedish Institute of Space Physics, Kiruna.
    Lindkvist, Jesper
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna.
    Holmström, Mats
    Swedish Institute of Space Physics, Kiruna.
    Stenberg-Wieser, Gabriella
    Swedish Institute of Space Physics, Kiruna.
    Ramstad, Robin
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.
    Götz, Charlotte
    Technicsche Universität Braunschweig, Institute for Geophysics an Extraterrestrial Physics, Braunschweig.
    Mass-loading of the solar wind at 67P/Churyumov-Gerasimenko: Observations and modelling2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 596, article id A42Article in journal (Refereed)
    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. 

  • 2.
    Behar, Etienne
    et al.
    Swedish Institute of Space Physics.
    Tabone, Benoit
    LERMA, Observatoire de Paris.
    Saillenfest, Melaine
    IMCCE, Observatoire de Paris.
    Henri, Pierre
    LPC2E, CNRS.
    Deca, Jan
    Laboratory for Atmospheric and Space Physics (LASP), University of Colorado Boulder.
    Lindkvist, Jesper
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Holmström, Mats
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics.
    Nilsson, Hans
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics.
    Solar wind dynamics around a comet: A 2D semi-analytical kinetic model2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed)
  • 3.
    Fatemi, Shahab
    et al.
    Swedish Institute of Space Physics.
    Poirier, Nicolas
    École nationale supérieure de mécanique et d’aérotechnique.
    Holmström, Mats
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics.
    Lindkvist, Jesper
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wieser, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics.
    Barabash, Stas
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics.
    A modelling approach to infer the solar wind dynamic pressure from magnetic field observations inside Mercury's magnetosphere2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed)
  • 4.
    Gunell, Herbert
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Belgium.
    Maggiolo, Romain
    Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Belgium.
    Nilsson, Hans
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics.
    Stenberg Wieser, Gabriella
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics.
    Slapak, Rikard
    EISCAT Scientific Association.
    Lindkvist, Jesper
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hamrin, Maria
    Umeå University, Faculty of Science and Technology, Department of Physics.
    De Keyser, Johan
    Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Belgium.
    Why an intrinsic magnetic field does not protect a planet against atmospheric escape2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed)
  • 5.
    Hamrin, Maria
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gunell, Herbert
    Umeå University, Faculty of Science and Technology, Department of Physics. Belgian Institute for Space Aeronomy, Brussels, Belgium.
    Lindkvist, Jesper
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lindqvist, Per-Arne
    Royal Institute of Technology, Stockholm, Sweden.
    Ergun, Robert E.
    Laboratory of Atmospheric and Space Physics, Boulder, CO, USA.
    Giles, Barbara L.
    NASA Goddard Space Flight Center, Greenbelt, MD, USA.
    Bow shock generator current systems: MMS observations of possible current closure2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, p. 242-258Article in journal (Refereed)
    Abstract [en]

    We use data from the first two dayside seasons of the Magnetospheric Multiscale (MMS) mission to study current systems associated with quasi‐perpendicular bow shocks of generator type. We have analyzed 154 MMS bow shock crossings near the equatorial plane. We compute the current density during the crossings and conclude that the component perpendicular to the shock normal (J⊥) is consistent with a pileup of the interplanetary magnetic field (IMF) inside the magnetosheath. For predominantly southward IMF, we observe a component Jn parallel (antiparallel) to the normal for GSM Y> 0 (<0), and oppositely directed for northward IMF. This indicates current closure across the equatorial magnetosheath, and it is observed for IMF clock angles near 0∘ and 180∘. To our knowledge, these are the first observational evidence for bow shock current closure across the magnetosheath. Since we observe no clear signatures of |J⊥| decreasing toward large |Y| we suggest that the main region of current closure is further tailward, outside MMS probing region. For IMF clock angles near 90∘, we find indications of the current system being tilted toward the north‐south direction, obtaining a significant Jz component, and we suggest that the current closes off the equatorial plane at higher latitudes where the spacecraft are not probing. The observations are complicated for several reasons. For example, variations in the solar wind and the magnetospheric currents and loads affect the closure, and Jn is distributed over large regions, making it difficult to resolve inside the magnetosheath proper.

  • 6.
    Khurana, Krishan K.
    et al.
    Institute of Geophysics and Planetary Physics and Dept. of Earth, Planetary and Space Sciences, University of California at Los Angeles, CA, 90095, USA.
    Fatemi, Shahab
    Space Sciences Laboratory, University of California, Berkeley, California, USA.
    Lindkvist, Jesper
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.
    Roussos, Elias
    Max Planck Institute, Göttingen, Germany.
    Krupp, Norbert
    Max Planck Institute, Göttingen, Germany.
    Holmström, Mats
    Swedish Institute of Space Physics, Kiruna.
    Russell, Christopher T.
    Institute of Geophysics and Planetary Physics and Dept. of Earth, Planetary and Space Sciences, University of California at Los Angeles, CA, 90095, USA.
    Dougherty, Michele K.
    Imperial College, London, U.K.
    The role of plasma slowdown in the generation of Rhea's Alfvén wings2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 2, p. 1778-1788Article in journal (Refereed)
    Abstract [en]

    Alfvén wings are known to form when a conducting or mass-loading object slows down a flowing plasma in its vicinity. Alfvén wings are not expected to be generated when an inert moon such as Rhea interacts with Saturn's magnetosphere, where the plasma impacting the moon is absorbed and the magnetic flux passes unimpeded through the moon. However, in two close polar passes of Rhea, Cassini clearly observed magnetic field signatures consistent with Alfvén wings. In addition, observations from a high-inclination flyby (Distance > 100 R Rh ) of Rhea on 3 June 2010 showed that the Alfvén wings continue to propagate away from Rhea even at this large distance. We have performed three-dimensional hybrid simulations of Rhea's interaction with Saturn's magnetosphere which show that the wake refilling process generates a plasma density gradient directed in the direction of corotating plasma. The resulting plasma pressure gradient exerts a force directed toward Rhea and slows down the plasma streaming into the wake along field lines. As on the same field lines, outside of the wake, the plasma continues to move close to its full speed, this differential motion of plasma bends the magnetic flux tubes, generating Alfvén wings in the wake. The current system excited by the Alfvén wings transfers momentum to the wake plasma extracting it from plasma outside the wake. Our work demonstrates that Alfvén wings can be excited even when a moon does not possess a conducting exosphere.

  • 7.
    Lindkvist, Jesper
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.
    Plasma Interactions with Icy Bodies in the Solar System2016Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 8.
    Lindkvist, Jesper
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hamrin, Maria
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gunell, Herbert
    Umeå University, Faculty of Science and Technology, Department of Physics. Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium.
    Nilsson, Hans
    Swedish Institute of Space Physics.
    Simon Wedlund, Cyril
    University of Oslo, Department of Physics, Oslo, Norway.
    Kallio, Esa
    Aalto University, Department of Electronics and Nanoengineering, Espoo, Finland.
    Mann, Ingrid
    University of Tromsø, Department of Physics and Technology, Tromsø, Norway.
    Pitkänen, Timo
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Karlsson, Tomas
    KTH Royal Institute of Technology, School of Electrical Engineering, Stockholm, Sweden.
    Energy conversion in cometary atmospheres: Hybrid modeling of 67P/Churyumov-Gerasimenko2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A81Article in journal (Refereed)
    Abstract [en]

    Aims. We wish to investigate the energy conversion between particles and electromagnetic fields and determine the location where it occurs in the plasma environment of comets.

    Methods. We used a hybrid plasma model that included photoionization, and we considered two cases of the solar extreme ultraviolet flux. Other parameters corresponded to the conditions of comet 67P/Churyumov-Gerasimenko at a heliocentric distance of 1.5 AU.

    Results. We find that a shock-like structure is formed upstream of the comet and acts as an electromagnetic generator, similar to the bow shock at Earth that slows down the solar wind. The Poynting flux transports electromagnetic energy toward the inner coma, where newly born cometary ions are accelerated. Upstream of the shock-like structure, we find local energy transfer from solar wind ions to cometary ions. We show that mass loading can be a local process with a direct transfer of energy, but also part of a dynamo system with electromagnetic generators and loads.

    Conclusions. The energization of cometary ions is governed by a dynamo system for weak ionization, but changes into a large conversion region with local transfer of energy directly from solar wind protons for high ionization.

  • 9.
    Lindkvist, Jesper
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.
    Holmström, Mats
    Swedish Institute of Space Physics, Kiruna.
    Fatemi, Shahab
    Space Sciences Laboratory, UC Berkeley.
    Wieser, Martin
    Swedish Institute of Space Physics, Kiruna.
    Barabash, Stas
    Swedish Institute of Space Physics, Kiruna.
    Ceres interaction with the solar wind2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 5, p. 2070-2077Article in journal (Refereed)
    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.

  • 10.
    Lindkvist, Jesper
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.
    Holmström, Mats
    Swedish Institute of Space Physics, Kiruna.
    Khurana, Krishan K.
    Department of Earth and Space Sciences, University of California, Los Angeles.
    Fatemi, Shahab
    Space Sciences Laboratory, University of California, Berkeley.
    Barabash, Stas
    Swedish Institute of Space Physics, Kiruna.
    Callisto plasma interactions: Hybrid modeling including induction by a subsurface ocean2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 6, p. 4877-4889Article in journal (Refereed)
    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.

  • 11.
    Pfleger, Martin
    et al.
    Institute for Chemical Engineering and Environmental Technology, Graz.
    Lindkvist, Jesper
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.
    Vorburger, Audrey
    Physikalisches Institut, University of Bern, Bern.
    Holmström, Mats
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.
    Lichtenegger, Herbert I. M.
    Space Research Institute, Austrian Academy of Sciences, Graz.
    Lammer, Helmut
    Space Research Institute, Austrian Academy of Sciences, Graz.
    Wurz, Peter
    Physikalisches Institut, University of Bern, Bern.
    Barabash, Stas
    Umeå University, Faculty of Science and Technology, Department of Physics. Swedish Institute of Space Physics, Kiruna.
    3D-modeling of Callisto's exosphere caused by thermal plasma sputtering2016In: Journal of Geophysical Research - Planets, ISSN 2169-9097, E-ISSN 2169-9100Article in journal (Other academic)
  • 12. Simon Wedlund, Cyril
    et al.
    Alho, Markku
    Gronoff, Guillaume
    Kallio, Esa
    Gunell, Herbert
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna.
    Lindkvist, Jesper
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Behar, Etienne
    Swedish Institute of Space Physics, Kiruna.
    Stenberg Wieser, Gabriella
    Swedish Institute of Space Physics, Kiruna.
    Miloch, Wojciech Jacek
    Hybrid modelling of cometary plasma environments: I. Impact of photoionisation, charge-exchange and electron ionisation on bow shock and cometopause at 67P/Churyumov-Gerasimenko2017In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 604, article id A73Article in journal (Refereed)
    Abstract [en]

    Context. The ESA/Rosetta mission made it possible to monitor the plasma environment of a comet, from near aphelion to perihelion conditions. To understand the complex dynamics and plasma structures found at the comet, a modelling effort must be carried out in parallel. Aims. Firstly, we present a 3D hybrid model of the cometary plasma environment including photoionisation, solar wind charge exchange, and electron ionisation reactions; this model is used in stationary and dynamic conditions (mimicking the solar wind variations), and is thus especially adapted to a weakly outgassing comet such as 67P/Churyumov-Gerasimenko, the target of the ESA/Rosetta mission. Secondly, we use the model to study the respective effects of ionisation processes on the formation of the dayside macroscopic magnetic and density boundaries upstream of comet 67P in perihelion conditions at 1.3 AU. Thirdly, we explore and discuss the effects of these processes on the magnetic field line draping, ionisation rates, and composition in the context of the Rosetta mission. Methods. We used a new quasi-neutral hybrid model, originally designed for weakly magnetised planetary bodies, such as Venus, Mars, and Titan, and adapted here to comets. Ionisation processes were monitored individually and together following a probabilistic interaction scheme. Three-dimensional paraboloid fits of the bow shock surface, identified for a magnetosonic Mach number equal to 2, and of the cometopause surface, were performed for a more quantitative analysis. Results. We show that charge exchange and electron ionisation play a major role in the formation of a bow shock-like structure far upstream, while photoionisation is the main driver at and below the cometopause boundary, within 1000 km cometocentric distance. Charge exchange contributes to 42% of the total production rate in the simulation box, whereas production rates from electron ionisation and photoionisation reach 33% and 25%, respectively. We also discuss implications for Rosetta's observations, regarding the detection of the bow shock and the cometopause.

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