author = {Edberg, Niklas J. T. and Alho, M. and Andr, M. and Andrews, D. J. and Behar, E. and Burch, J. L. and Carr, C. M. and Cupido, E. and Engelhardt, I. A. D. and Eriksson, A. I. and Glassmeier, K.-H. and Goetz, C. and Goldstein, R. and Henri, P. and Johansson, F. L. and Koenders, C. and Mandt, K. and Möstl, C. and Nilsson, H. and Odelstad, E. and Richter, I. and Simon Wedlund, C. and Stenberg Wieser, G. and Szego, K. and Vigren, E. and Volwerk, M.},
  title = {CME impact on comet 67P/Churyumov-Gerasimenko},
  volume = {462},
  number = {Suppl 1},
  pages = {S45-S56},
  year = {2016},
  doi = {10.1093/mnras/stw2112},
  abstract = {We present Rosetta observations from comet 67P/Churyumov-Gerasimenko during the impact of a coronal mass ejection (CME). The CME impacted on 2015 Oct 5-6, when Rosetta was about 800 km from the comet nucleus, and 1.4 au from the Sun. Upon impact, the plasma environment is compressed to the level that solar wind ions, not seen a few days earlier when at 1500 km, now reach Rosetta. In response to the compression, the flux of suprathermal electrons increases by a factor of 5-10 and the background magnetic field strength increases by a factor of 2.5. The plasma density increases by a factor of 10 and reaches 600 cm3, due to increased particle impact ionization, charge exchange and the adiabatic compression of the plasma environment. We also observe unprecedentedly large magnetic field spikes at 800 km, reaching above 200 nT, which are interpreted as magnetic flux ropes. We suggest that these could possibly be formed by magnetic reconnection processes in the coma as the magnetic field across the CME changes polarity, or as a consequence of strong shears causing Kelvin-Helmholtz instabilities in the plasma flow. Due to the limited orbit of Rosetta, we are not able to observe if a tail disconnection occurs during the CME impact, which could be expected based on previous remote observations of other CME-comet interactions.},
  url = {},
  eprint = {},
  journal = {Monthly Notices of the Royal Astronomical Society}
  author = {{Simon Wedlund, C.} and {Kallio, E.} and {Alho, M.} and {Nilsson, H.} and {Stenberg Wieser, G.} and {Gunell, H.} and {Behar, E.} and {Pusa, J.} and {Gronoff, G.}},
  title = {The atmosphere of comet 67P/Churyumov-Gerasimenko diagnosed by charge-exchanged solar wind alpha particles},
  doi = {10.1051/0004-6361/201527532},
  url = {},
  journal = {A&A},
  year = 2016,
  volume = 587,
  pages = {A154},
  month = {}
  author = {Wang, X.-D. and Alho, M. and Jarvinen, R. and Kallio, E. and Barabash, S. and Futaana, Y.},
  title = {Emission of Hydrogen Energetic Neutral Atoms from the Martian Subsolar Magnetosheath},
  journal = {Journal of Geophysical Research: Space Physics},
  issn = {2169-9402},
  url = {},
  doi = {10.1002/2015JA021653},
  pages = {n/a--n/a},
  keywords = {Solar wind interactions with unmagnetized bodies, Mars, Charged particle motion and acceleration, Mathematical and numerical techniques, MHD waves and instabilities, Mars, energetic neutral atom, numerical simulation, dayside interaction, hybrid simulation},
  year = {2015},
  note = {2015JA021653},
  abstract = {We have simulated the hydrogen energetic neutral atom (ENA) emissions from the subsolar magnetosheath of Mars using a hybrid model of the proton plasma [Kallio et al., 2010] charge-exchanging with the Martian exosphere to study statistical features revealed from the observations of the Neutral Particle Detectors on Mars Express [Wang et al., 2013]. The simulations reproduce well the observed enhancement of the hydrogen ENA emissions from the dayside magnetosheath in directions perpendicular to the Sun-Mars line. Our results show that the neutralized protons from the shocked solar wind are the dominant ENA population rather than those originating from the pickup planetary ions. The simulation also suggests that the observed stronger ENA emissions in the direction opposite to the solar wind convective electric field result from a stronger proton flux in the same direction at the lower magnetosheath, i.e., the proton fluxes in the magnetosheath are not cylindrically symmetric. We also confirm the observed increasing of the ENA fluxes with the solar wind dynamical pressure in the simulations. This feature is associated with a low altitude of the induced magnetic boundary when the dynamic pressure is high and the magnetosheath protons can reach to a denser exosphere and thus the charge exchange rate becomes higher. Overall, the analysis suggests that kinetic effects play an important and pronounced role in the morphology of the hydrogen ENA distribution and the plasma environment at Mars in general.}
  title = {3D-modeling of Mercury's solar wind sputtered surface-exosphere environment },
  journal = {Planetary and Space Science },
  volume = {115},
  number = {},
  pages = {90 - 101},
  year = {2015},
  note = {Solar wind interaction with the terrestrial planets },
  issn = {0032-0633},
  doi = {},
  url = {},
  author = {M. Pfleger and H.I.M. Lichtenegger and P. Wurz and H. Lammer and E. Kallio and M. Alho and A. Mura and S. McKenna-Lawlor and J.A. Martín-Fernández},
  keywords = {Mercury},
  keywords = {Messenger},
  keywords = {BepiColombo},
  keywords = {Surface sputtering},
  keywords = {Exosphere},
  keywords = {Particle release },
  abstract = {Abstract The efficiency of sputtered refractory elements by H + and He++ solar wind ions from Mercury's surface and their contribution to the exosphere are studied for various solar wind conditions. A 3D solar wind–planetary interaction hybrid model is used for the evaluation of precipitation maps of the sputter agents on Mercury's surface. By assuming a global mineralogical surface composition, the related sputter yields are calculated by means of the 2013 \{SRIM\} code and are coupled with a 3D exosphere model. Because of Mercury's magnetic field, for quiet and nominal solar wind conditions the plasma can only precipitate around the polar areas, while for extreme solar events (fast solar wind, coronal mass ejections, interplanetary magnetic clouds) the solar wind plasma has access to the entire dayside. In that case the release of particles form the planet's surface can result in an exosphere density increase of more than one order of magnitude. The corresponding escape rates are also about an order of magnitude higher. Moreover, the amount of He++ ions in the precipitating solar plasma flow enhances also the release of sputtered elements from the surface in the exosphere. A comparison of our model results with \{MESSENGER\} observations of sputtered Mg and Ca elements in the exosphere shows a reasonable quantitative agreement. }
  title = {Dust environment of an airless object: A phase space study with kinetic models },
  journal = {Planetary and Space Science },
  volume = {},
  number = {},
  pages = { - },
  year = {2015},
  note = {},
  issn = {0032-0633},
  doi = {},
  url = {},
  author = {E. Kallio and S. Dyadechkin and S. Fatemi and M. Holmström and Y. Futaana and P. Wurz and V.A. Fernandes and F. Álvarez and J. Heilimo and R. Jarvinen and W. Schmidt and A.-M. Harri and S. Barabash and J. Mäkelä and N. Porjo and M. Alho},
  keywords = {Dust},
  keywords = {Moon},
  keywords = {asteroids},
  keywords = {Plasma–surface interaction},
  keywords = {Kinetic particle simulations},
  keywords = {Space plasma },
  abstract = {Abstract The study of dust above the lunar surface is important for both science and technology. Dust particles are electrically charged due to impact of the solar radiation and the solar wind plasma and, therefore, they affect the plasma above the lunar surface. Dust is also a health hazard for crewed missions because micron and sub-micron sized dust particles can be toxic and harmful to the human body. Dust also causes malfunctions in mechanical devices and is therefore a risk for spacecraft and instruments on the lunar surface. Properties of dust particles above the lunar surface are not fully known. However, it can be stated that their large surface area to volume ratio due to their irregular shape, broken chemical bonds on the surface of each dust particle, together with the reduced lunar environment cause the dust particles to be chemically very reactive. One critical unknown factor is the electric field and the electric potential near the lunar surface. We have developed a modelling suite, Dusty Plasma Environments: near-surface characterisation and Modelling (DPEM), to study globally and locally dust environments of the Moon and other airless bodies. The \{DPEM\} model combines three independent kinetic models: (1) a 3D hybrid model, where ions are modelled as particles and electrons are modelled as a charged neutralising fluid, (2) a 2D electrostatic Particle-in-Cell (PIC) model where both ions and electrons are treated as particles, and (3) a 3D Monte Carlo (MC) model where dust particles are modelled as test particles. The three models are linked to each other unidirectionally; the hybrid model provides upstream plasma parameters to be used as boundary conditions for the \{PIC\} model which generates the surface potential for the \{MC\} model. We have used the \{DPEM\} model to study properties of dust particles injected from the surface of airless objects such as the Moon, the Martian moon Phobos and the asteroid RQ36. We have performed a (v0, m/q)-phase space study where the property of dust particles at different initial velocity (v0) and initial mass per charge (m/q) ratio were analysed. The study especially identifies regions in the phase space where the electric field within a non-quasineutral plasma region above the surface of the object, the Debye layer, becomes important compared with the gravitational force. Properties of the dust particles in the phase space region where the electric field plays an important role are studied by a 3D Monte Carlo model. The current \{DPEM\} modelling suite does not include models of how dust particles are initially injected from the surface. Therefore, the presented phase space study cannot give absolute 3D dust density distributions around the analysed airless objects. For that, an additional emission model is necessary, which determines how many dust particles are emitted at various places on the analysed (v0, m/q)-phase space. However, this study identifies phase space regions where the electric field within the Debye layer plays an important role for dust particles. Overall, the initial results indicate that when a realistic dust emission model is available, the unified lunar based \{DPEM\} modelling suite is a powerful tool to study globally and locally the dust environments of airless bodies such as planetary moons, Mercury, asteroids and non-active comets far from the Sun. }
  title = {Paleo Mars energetic particle precipitation },
  journal = {Planetary and Space Science },
  volume = {119},
  number = {},
  pages = {103 - 110},
  year = {2015},
  note = {},
  issn = {0032-0633},
  doi = {},
  url = {},
  author = {Markku Alho and Susan McKenna-Lawlor and Esa Kallio},
  keywords = {Mars},
  keywords = {Solar energetic particles},
  keywords = {Magnetosphere},
  keywords = {Young Mars},
  keywords = {Upper atmosphere},
  keywords = {Ionosphere},
  keywords = {Precipitation },
  abstract = {Abstract A young Mars may well have possessed a global dipolar magnetic field that provided protection for the planet׳s atmosphere from the space weather environment. Against this background, we study in the present paper the effect of various dipole magnetic fields on particle precipitation (range 10 keV–4.5 MeV) on the upper Martian atmosphere as the magnetosphere gradually declined to become an induced magnetosphere. We utilized a hybrid plasma model to provide, in a self-consistent fashion, simulations (that included ion-kinetic effects) of the interaction between the Martian obstacle (magnetized or otherwise) and the solar wind. Besides the intrinsic dipole, with field strengths of ~100 nT and below, we assume modern solar and atmospheric parameters to examine the effect of the single variable, that is the dipole strength. We thereby investigated the precipitation of solar energetic particles on the upper atmosphere of the planet in circumstances characterized by the evolution of a diminishing Martian dynamo that initially generated an ideal dipolar field. It is demonstrated that an assumed Martian dipole would have provided, in the energy range investigated, significant shielding against proton impingement and that the interaction between the solar wind and the assumed Martian magnetic dipole would have been responsible for generating the shielding effect identified. }
  title = {Acceleration of ions and nano dust at a comet in the solar wind },
  journal = {Planetary and Space Science },
  volume = {119},
  number = {},
  pages = {13 - 23},
  year = {2015},
  note = {},
  issn = {0032-0633},
  doi = {},
  url = {},
  author = {H. Gunell and I. Mann and C. Simon Wedlund and E. Kallio and M. Alho and H. Nilsson and J. De Keyser and F. Dhooghe and R. Maggiolo},
  keywords = {Comet},
  keywords = {Dust},
  keywords = {Hybrid model },
  abstract = {Abstract A quasi-neutral hybrid simulation of the interaction of the solar wind with the atmosphere of a comet is used together with a test particle simulation of cometary ions and dust to compute trajectories and velocity distribution functions of charged particles, starting outside the diamagnetic cavity at 150 km cometocentric distance. The simulations are run with parameters suited to make predictions for comet 67P/Churyumov–Gerasimenko when it is at a heliocentric distance of 1.45 AU. It is found that the shape of the ion trajectories depends on the location of the source, and that a velocity distribution that is observed at a given point in space is influenced by the spatial structure of the source. Charged dust grains with radii in the 1–10 nm range are accelerated from the nucleus to a distance of 2.9 × 10 4 km in between 15 min and 2 h approximately. Dust particles smaller than 10 nm in radius are accelerated to speeds over 10 km/s. }
  author = {Vech, D. and Szego, K. and Opitz, A. and Kajdic, P. and Fraenz, M. and Kallio, E. and Alho, M.},
  title = {Space weather effects on the bow shock, the magnetic barrier, and the ion composition boundary at Venus},
  journal = {Journal of Geophysical Research: Space Physics},
  volume = {120},
  number = {6},
  issn = {2169-9402},
  url = {},
  doi = {10.1002/2014JA020782},
  pages = {4613--4627},
  keywords = {Coronal mass ejections, Venus, Shock waves, Solar effects, Venus, interplanetary coronal mass ejections, plasma interaction, bow shock, ion composition boundary, magnetic barrier},
  year = {2015},
  note = {2014JA020782}
  author = {{Jarvinen}, R. and {Alho}, M. and {Kallio}, E. and {Wurz}, P. and 
	{Barabash}, S. and {Futaana}, Y.},
  title = {{On vertical electric fields at lunar magnetic anomalies}},
  journal = {Geophysical Research Letters},
  keywords = {lunar, magnetic anomalies, solar wind, electric field, potential, Hall field},
  year = 2014,
  month = apr,
  volume = 41,
  pages = {2243-2249},
  abstract = {{We study the interaction between a magnetic dipole mimicking the
Gerasimovich magnetic anomaly on the lunar surface and the solar wind in
a self-consistent 3-D quasi-neutral hybrid simulation where ions are
modeled as particles and electrons as a charge-neutralizing fluid.
Especially, we consider the origin of the recently observed electric
potentials at lunar magnetic anomalies. An antimoonward Hall electric
field forms in our simulation resulting in a potential difference of
{\lt}300V on the lunar surface, in which the value is similar to
observations. Since the hybrid model assumes charge neutrality, our
results suggest that the electric potentials at lunar magnetic anomalies
can be formed by decoupling of ion and electron motion even without
charge separation.
  doi = {10.1002/2014GL059788},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
  author = {{Kallio}, E. and {McKenna-Lawlor}, S. and {Alho}, M. and {Jarvinen}, R. and 
	{Dyadechkin}, S. and {Afonin}, V.~V.},
  title = {{Energetic protons at Mars: interpretation of SLED/Phobos-2 observations by a kinetic model}},
  journal = {Annales Geophysicae},
  year = 2012,
  month = nov,
  volume = 30,
  pages = {1595-1609},
  abstract = {{Mars has neither a significant global intrinsic magnetic field nor a
dense atmosphere. Therefore, solar energetic particles (SEPs) from the
Sun can penetrate close to the planet (under some circumstances reaching
the surface). On 13 March 1989 the SLED instrument aboard the Phobos-2
spacecraft recorded the presence of SEPs near Mars while traversing a
circular orbit (at 2.8 R$_{M}$). In the present study the response
of the Martian plasma environment to SEP impingement on 13 March was
simulated using a kinetic model. The electric and magnetic fields were
derived using a 3-D self-consistent hybrid model (HYB-Mars) where ions
are modelled as particles while electrons form a massless charge
neutralizing fluid. The case study shows that the model successfully
reproduced several of the observed features of the in situ observations:
(1) a flux enhancement near the inbound bow shock, (2) the formation of
a magnetic shadow where the energetic particle flux was decreased
relative to its solar wind values, (3) the energy dependency of the flux
enhancement near the bow shock and (4) how the size of the magnetic
shadow depends on the incident particle energy. Overall, it is
demonstrated that the Martian magnetic field environment resulting from
the Mars-solar wind interaction significantly modulated the Martian
energetic particle environment.
  doi = {10.5194/angeo-30-1595-2012},
  adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}

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