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Friday, June 23, 2017

Astrophysicists have dealt with the interaction between the solar wind and comets

Scientists have constructed a three-dimensional model for the dynamics of particles around the comet. The work identified a complex interaction of different components: electrons and protons of the solar wind electrons and ions emitted from the surface of a solid body. The results are applicable in particular to the comet Churyumov-Gerasimenko, published in the journal Physical Review Letters.

Photo: J. Deca et al., Phys. Rev. Lett. (2017)

The solar wind is a supersonic flow of particles emanating from the sun. It was his interaction with the nuclei of the comets causes them glow coma and tails in some cases. Like the wind, and the gas in the halo of comets are collisionless environment, that is, their constituent particles do not interact directly. However, their dynamics are linked via large-scale electromagnetic fields, so in General they form a multicomponent plasma, which behaves like a weakly interacting multiple fluids occupying the same space.

American astrophysicists have applied to this task, method of particles in cells, designed for such situations: they describe the plasma as a set of separate noninteracting particles, which collectively alter the electromagnetic field, defined in a separate cell space. The masses and charges of the simulated particles is much larger than the real, but in General they produce more complex behaviour than would be obtained in a fully hydrodynamic model.

Probe Rosetta noted several unusual phenomena around the comet Churyumov-Gerasimenko. Near it there are two populations of electrons with different temperatures. In the simulation managed to reproduce one of the proposed mechanisms: the selection of more hot electrons, since the ions have lower energy and form a region of positive potential, which can be removed only electrons with high energy. However, alternative explanations, such as the acceleration in the electromagnetic field or generated by albinowski waves regions with nonzero electric field, not refuted completely.

The scientists also found that the simulated components is amazingly effective exchange particles at large spatial scales: for example, the electron wind and the comet’s roles change in the surroundings during the interaction. It is connected with different behavior of electrons and protons of the wind due to the different ratio of charge to mass of these particles. The magnetic field lines frozen into the plasma of the wind, envelop the comet that causes a component of the field guiding charged particles around it. However, due to the large mass, protons are only slightly deflected by this field and penetrate much closer to the nucleus. In General, these processes lead to transfer of momentum from the wind to particles of the comet, which leads to a fast capture of the last and their passion flows from the sun.

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