Search

Magnetospheres at ion kinetic scales, or mini-magnetospheres, possess unusual features as predicted by numerical simulations. However, there are practically no data on the subject from space observations and the data which are available are far too incomplete. In this paper we describe the results of a laboratory experiment on the interaction of plasma flow with a magnetic dipole with parameters such that the ion inertial length is larger than the size of an observed magnetosphere. A detailed structure of the non-coplanar or out-of-plane component of the magnetic field has been obtained in the meridian plane. The independence of this component on dipole moment reversal, as was reported in a previous work, has been verified. In the tail distinct lobes and a central current sheet have been observed. It was found that lobe regions adjacent to boundary layer are dominated by a non-coplanar component of magnetic field. Tail-ward oriented electric current in the plasma associated with that component appears to be equal to the ion current in the upstream part of magnetosphere and in the tail current sheet implying that electrons are stationary in those regions while the ions flow by. The data obtained strongly support the proposed model of mini-magnetosphere based on two-fluid effects as described by the Hall term. [ABSTRACT FROM AUTHOR]

In the present series of papers we propose a consistent description of the mass loss process. To study in a comprehensive way the effects of the intrinsic magnetic field of a close-orbit giant exoplanet (a so-called hot Jupiter) on atmospheric material escape and the formation of a planetary inner magnetosphere, we start with a hydrodynamic model of an upper atmosphere expansion in this paper. While considering a simple hydrogen atmosphere model, we focus on the self-consistent inclusion of the effects of radiative heating and ionization of the atmospheric gas with its consequent expansion in the outer space. Primary attention is paid to an investigation of the role of the specific conditions at the inner and outer boundaries of the simulation domain, under which different regimes of material escape (free and restricted flow) are formed. A comparative study is performed of different processes, such as X-ray and ultraviolet (XUV) heating, material ionization and recombination, cooling, adiabatic and Lyα cooling, and Lyα reabsorption. We confirm the basic consistency of the outcomes of our modeling with the results of other hydrodynamic models of expanding planetary atmospheres. In particular, we determine that, under the typical conditions of an orbital distance of 0.05 AU around a Sun-type star, a hot Jupiter plasma envelope may reach maximum temperatures up to ∼9000 K with a hydrodynamic escape speed of ∼9 km s–1, resulting in mass loss rates of ∼(4-7) · 1010 g s–1. In the range of the considered stellar-planetary parameters and XUV fluxes, that is close to the mass loss in the energy-limited case. The inclusion of planetary intrinsic magnetic fields in the model is a subject of the follow-up paper (Paper II). [ABSTRACT FROM AUTHOR]

Giant exoplanets at close orbits, or so-called hot Jupiters, are supposed to have an intensive escape of upper atmospheric material heated and ionized by the radiation of a host star. An interaction between outflowing atmospheric plasma and the intrinsic planetary magnetic dipole field leads to the formation of a crucial feature of a hot Jupiter's magnetosphere—an equatorial current-carrying magnetodisk. The presence of a magnetodisk has been shown to influence the topology of a hot Jupiter's magnetosphere and to change a standoff distance of the magnetopause. In this paper, the basic features of the formation of a hot Jupiter's magnetodisk are studied by means of a laboratory experiment. A localized central source produces plasma that expands outward from the surface of the dipole and inflates the magnetic field. The observed structure of magnetic fields, electric currents, and plasma density indicates the formation of a relatively thin current disk extending beyond the Alfvénic point. At the edge of the current disk, an induced magnetic field was found to be several times larger than the field of the initial dipole. [ABSTRACT FROM AUTHOR]