The strong effect of electron thermal conduction on the global structure of the heliosphere

Voyager 1 and 2 crossed the heliopause at $\sim$122 AU in 2012 and $\sim$119 AU in 2018, respectively. It was quite a surprise because the thickness of the inner heliosheath obtained by the existing at that time models of the global heliosphere was significantly larger (by 20-40 AU). Until now, the problem of the heliosheath thickness has not been fully resolved. Earlier in the frame of an oversimplified toy model of nearly isothermal solar wind plasma it has been shown that the effect of electron thermal conduction may significantly reduce the thickness of the inner heliosheath. In this paper, we present the first results of our 3D kinetic-MHD model of the global heliosphere, where the effect of thermal electron conduction has been considered rigorously. The thermal conduction acts mainly along the magnetic field lines. Classical and saturated thermal fluxes are employed when appropriate. It is shown the effects of thermal conduction are significant. The thickness of the inner heliospheric is reduced. It is desired effect since it helps to reconcile the thickness obtained in the model with Voyager data. The other effects are the strong depletion of the heliosheath plasma temperature toward the heliopause and the increase of the plasma temperature in the supersonic solar wind upstream of the termination shock.Comment: 7 pages, 5 figures, accepted for publication in MNRA

Scatter-free pickup ions beyond the heliopause as a model for the Interstellar Boundary Explorer (IBEX) ribbon

We present new kinetic-gasdynamic model of the solar wind interaction with the local interstellar medium. The model incorporates several processes suggested by McComas et al. (2009) for the origin of the heliospheric ENA ribbon -- the most prominent feature seen in the all sky maps of heliospheric ENAs discovered by the Interstellar Boundary Explorer (IBEX). The ribbon is a region of enhanced fluxes of ENAs crossing almost the entire sky. Soon after the ribbon's discovery it was realized (McComas et al., 2009) that the enhancement of the fluxes could be in the directions where the radial component of the interstellar magnetic field around the heliopause is close to zero (Schwadron et al., 2009). Our model includes secondary charge exchange of the interstellar H atoms with the interstellar pickup protons outside the heliopause and is a further advancement of the kinetic-gasdynamic model by Malama et al. (2006) where pickup protons were treated as a separate kinetic component. Izmodenov et al. (2009) have shown in the frame of Malama's model that the interstellar pickup protons outside the heliopause maybe a significant source of ENAs at energies above 1 keV. The difference between the current work and that of Izmodenov et al. (2009) is in the assumption of no-scattering for newly created pickup protons outside the heliopause. In this limit the model produces a feature qualitatively similar to the ribbon observed by IBEX.Comment: submitted to ApJ

Heating of the solar wind in the outer heliosphere

International audienceSmall-scale Alfvènic turbulence in the outer heliosphere is mainly determined by a source which is connected with the instability of the initially highly anisotropic velocity distribution of interstellar pick-up protons. The main portion of the generated turbulent energy is subsequently absorbed by the pick-up protons themselves due to the cyclotron-resonant interaction between waves and particles. A small fraction of this energy can be transferred to solar wind protons resulting in their heating. The heating is more efficient in the high-speed solar wind

Adiabatic energy change in the inner heliosheath: How does it affect the distribution of pickup protons and energetic neutral atom fluxes?

The hydrogen atoms penetrate the heliosphere from the local interstellar medium, and while being ionized, they form the population of pickup protons. The distribution of pickup protons is modified by the adiabatic heating (cooling) induced by the solar wind plasma compression (expansion). In this study, we emphasize the importance of the adiabatic energy change in the inner heliosheath that is usually either neglected or considered improperly. The effect of this process on the energy and spatial distributions of pickup protons and energetic neutral atoms (ENAs), which originate in the charge exchange of pickup protons, has been investigated and quantified using a kinetic model. The model employs the global distributions of plasma and hydrogen atoms in the heliosphere from the simulations of a kinetic-magnetohydrodynamic model of solar wind interaction with the local interstellar medium. The findings indicate that the adiabatic energy change is responsible for the broadening of the pickup proton velocity distribution and the significant enhancement of ENA fluxes (up to $\sim$5 and $\sim$20 times in the upwind and downwind directions at energies $\sim$1-2 keV for an observer at 1 au). It sheds light on the role of adiabatic energy change in explaining the discrepancies between the ENA flux observations and the results of numerical simulations.Comment: 7 pages, 4 figures; accepted for publication in MNRA

Analysis of the IBEX-Lo interstellar hydrogen fluxes collected in 2009–2018 as a tool for sensing of the solar radiation pressure and the hydrogen ionization rate

The Interstellar Boundary Explorer (IBEX) has been measuring interstellar hydrogen fluxes at 1 au since 2009. In this paper,we analysed all available data obtained with the IBEX-Lo instrument at energies 11–41 eV using our numerical kinetic modelof the interstellar hydrogen distribution in the heliosphere. We performed a fitting of the data to find independently the modelparameters: the ratio of the solar radiation pressure to the solar gravitation (μ0), ionization rate of hydrogen atoms at 1 au(β0), parameters of the secondary interstellar atoms at 70 au from the Sun, which provide the best agreement with the data byminimization of metricχ2. We also analysed temporal variations of the ratio of the fluxes measured in a fixed direction at energybin 1 and energy bin 2. It is found that in 2009–2011 and 2017–2016 the ratio provided by the model is smaller than in the IBEX-Lo data, while in 2012–2015, oppositely, the model ratio is larger compared to the data. This might be caused by the incorrectseparation of the measured fluxes between energy channels in the data, or by some additional physical factors that are omitted inthe model. Understanding this issue may be important for the preparation of future Interstellar Mapping and Acceleration Probemission. At this stage, we relied on the sum of the fluxes measured in energy bins 1 and 2 for comparison to model predictions