I. F. Shaikhislamov

ATMOSPHERE EXPANSION AND MASS LOSS OF CLOSE-ORBIT GIANT EXOPLANETS HEATED BY STELLAR XUV. II. EFFECTS OF PLANETARY MAGNETIC FIELD; STRUCTURING OF INNER MAGNETOSPHERE

This is the second paper in a series where we build a self-consistent model to simulate the mass-loss process of a close-orbit magnetized giant exoplanet, so-called hot Jupiter (HJ). In this paper we generalize the hydrodynamic (HD) model of an HJ expanding hydrogen atmosphere, proposed in the first paper, to include the effects of intrinsic planetary magnetic field. The proposed self-consistent axisymmetric 2D magnetohydrodynamics model incorporates radiative heating and ionization of the atmospheric gas, basic hydrogen chemistry for the appropriate account of major species composing HJs upper atmosphere and related radiative energy deposition, and H3+ and Ly{\alpha} cooling processes. The model also takes into account a realistic solar-type X-ray/EUV spectrum for calculation of intensity and column density distribution of the radiative energy input, as well as gravitational and rotational forces acting in a tidally locked planet-star system. An interaction between the expanding atmospheric plasma and an intrinsic planetary magnetic dipole field leads to the formation of a current-carrying magnetodisk that plays an important role for topology and scaling of the planetary magnetosphere. A cyclic character of the magnetodisk behavior, composed of consequent phases of the disk formation followed by the magnetic reconnection with the ejection of a ring-type plasmoid, has been discovered and investigated. We found that the mass-loss rate of an HD 209458b analog planet is weakly affected by the equatorial surface field <0.3 G, but is suppressed by an order of magnitude at the field of 1 G.

Experimental study of a mini-magnetosphere

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.

Laboratory simulation of field aligned currents in an experiment on laser-produced plasma interacting with a magnetic dipole

In an experiment on a magnetic dipole interacting with a laser-produced plasma the generation of an intense field aligned current (FAC) system was observed for the first time in a laboratory. The detailed measurements of the total value and local current density, of the magnetic field at the poles and in the equatorial magnetopause, and particular features of electron motion in the current channels revealed its similarity to the Region-1 current system in the Earth magnetosphere. Such currents were found to exist only if they can close via conductive cover of the dipole. Comparison of conductive and dielectric cases revealed specific magnetic features produced by FAC and their connection with electric potential generated in the equatorial part of the magnetopause. To interpret the data we consider a model of electric potential generation in the boundary layer which agrees with experiment and with measurements of the Earths transpolar potential in the absence of an interplanetary magnetic field as well. The results could be of importance for the investigation of Mercury as a magnetic disturbance due to FAC could be especially large because of the small size of the Hermean magnetosphere.

Laser Plasma Experiments to Simulate Coronal Mass Ejections During Giant Solar Flare and Their Strong Impact on Magnetospheres

Giant solar flares are the most powerful phenomenon in the solar system, which can strongly affect various geospheres and technical systems in the near Earths space or its surface. During the space era, only few events with a total energy of more than 1034 erg happened, and probably, only one of these ldquowas directedrdquo to the Earth (August 4, 1972). In this paper, we report on the first attempts to simulate in a laboratory both the initial (at the Sun) and final (near the Earth) stages of relevant interaction processes between the plasma flows and magnetic fields. By using laser-produced plasmas and intense magnetic dipole, we performed two types of simulation experiments: 1) on the interaction of ejected solar plasma flows with/in dipole magnetic field and 2) on the extreme (three fold) compression of the Earths magnetopause by giant coronal mass ejections from the Sun. General physical conditions of these phenomena are briefly described, and the developed methods of laboratory simulation and numerical modeling of various explosive processes in collisionless space plasmas are discussed on the basis of relevant dimensionless criteria of the problems.

Experimental study of collisionless super-Alfvénic interaction of interpenetrating plasma flows

An experiment on the interaction between an expanding super-Alfvénic laser-produced plasma flow and a magnetized background plasma under conditions in which the ion gyroradius is comparable with the characteristic scale length of magnetic field displacement is described. The depletion of the background plasma in a substantial volume and the formation of a large-amplitude compression pulse propagating with a super-Alfvénic velocity are revealed. The efficiency of energy conversion into perturbations of the background plasma was found to be 25%. Combined data from magnetic, electric, and plasma measurements indicate that the interaction occurs via the magnetic laminar mechanism.

INFLATION OF A DIPOLE FIELD IN LABORATORY EXPERIMENTS: TOWARD AN UNDERSTANDING OF MAGNETODISK FORMATION IN THE MAGNETOSPHERE OF A HOT JUPITER

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 Jupiters magnetosphere—an equatorial current-carrying magnetodisk. The presence of a magnetodisk has been shown to influence the topology of a hot Jupiters magnetosphere and to change a standoff distance of the magnetopause. In this paper, the basic features of the formation of a hot Jupiters 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 Alfvenic 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.

Charge-exchange pumping of laser-produced plasma colliding with vapour cloud for lasing in XUV

A charge-exchange pumping of laser-produced ions on a compact gas cloud is experimentally investigated. An interaction at density of neutrals has been achieved for the first time. A record efficiency of charge-transfer pumping 10% has been measured which is close to maximum 25% predicted by developed analytical model. The intensity of VUV-emission from the region amounted to 1 MW with duration ns. The results obtained are promising for future laser gain experiments.

Laboratory experiment on region-1 field-aligned current and its origin in the low-latitude boundary layer

In previous experiments by the authors on a magnetic dipole interacting with a laser-produced plasma the generation of an intense field-aligned current (FAC) system on terrella poles was observed. In this paper the question of the origin of these currents in a low-latitude boundary layer of magnetosphere is investigated. Experimental evidence of such a link was obtained by measurements of the magnetic field generated by tangential drag and sheared stress. This specific azimuthal field was found to have quadruple symmetry and local maxima inside the magnetosphere adjacent to the boundary layer. Cases of metallic and dielectric dipole covers modeling good conductive and non-conductive ionosphere revealed that the presence or absence of FACs results in different amplitudes and spatial structures of the sheared field. The current associated with the azimuthal field flows upward at the dawnside, and toward the equator plane at the duskside. It was found to coincide by direction and to correspond by amplitude to a total cross-polar current measured independently. The results suggest that compressional and Alfven waves are responsible for FAC generation. The study is most relevant to FAC generation in the magnetospheres of Earth and Mercury following pressure jumps in solar wind.

Simulation of astrophysical plasma dynamics in the laser experiments

The properties of laser‐produced plasma are similar in many features to the ones of various space plasma releases of explosive nature. It allows to investigate the processes of an interaction of those plasmas with background media by the means of laboratory simulation. In the given paper such simulation experiments with quasispherical plasma clouds at KI‐1 laser facility are presented. The experiments are related to dynamics of collisionless expansion of exploding space plasmas in the surrounding magnetized media at various Alfven‐Much numbers. A non‐uniform media as well has been simulated. The results on generation of shock and wistler waves in background, on formation of diamagnetic cavity and flute instability of plasma clouds are described. Data on a dynamics of laser‐produced plasma in a dipole magnetic field are presented also. Results are analyzed in connection with dynamics of Supernova remnants in interstellar medium, Barium releases in Earth magnetosphere and possible disturbances of the latter...

Lyα Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions

To shed more light on the nature of the observed Ly{\alpha} absorption during transits of HD 209458b and to quantify the major mechanisms responsible for the production of fast hydrogen atoms (the so called energetic neutral atoms, ENAs) around the planet, 2D hydrodynamic multifluid modeling of the expanding planetary upper atmosphere, which is driven by stellar XUV, and its interaction with the stellar wind has been performed. The model selfconsistently describes the escaping planetary wind, taking into account the generation of ENAs due to particle acceleration by the radiation pressure and by the charge exchange between the stellar wind protons and planetary atoms. The calculations in a wide range of stellar wind parameters and XUV flux values showed that under typical Sun-like star conditions, the amount of generated ENAs is too small, and the observed absorption at the level of 6-8 percent can be attributed only to the non-resonant natural line broadening. For lower XUV fluxes, e.g., during the activity minima, the number of planetary atoms that survive photoionization and give rise to ENAs increases, resulting in up to 10-15 percent absorption at the blue wing of the Lya line, caused by resonant thermal line broadening. A similar asymmetric absorption can be seen under the conditions realized during coronal mass ejections, when sufficiently high stellar wind pressure confines the escaping planetary material within a kind of bowshock around the planet. It was found that the radiation pressure in all considered cases has a negligible contribution to the production of ENAs and the corresponding absorption.