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We simulate with a global 3D aeronomy code two warm Neptunes in the TOI-421 system and show that both planets experience significant escape of their upper atmospheres. The double shock structures, generated around the planets in course of their interaction with the stellar wind (SW) plasma flow are revealed. The calculations of stellar Ly α transit absorption by the planets reveal that it reaches a detectable level only for a moderate or strong SW, with a sufficiently high density. In this case, the energetic neutral atoms provide significant absorption at the high velocity blue wing of the Ly α line, whereas the corresponding transit light curves exhibit an early ingress and extended egress features. With the same code, we also modelled the absorption at the position of the 10 830 Å line of the metastable helium, showing that it can be detected only for the farthest planet of the considered two, if the helium abundance is comparable to the solar value. [ABSTRACT FROM AUTHOR]

The signs of an expanding atmosphere of HD209458b have been observed with far-ultraviolet transmission spectroscopy and in the measurements of transit absorption by metastable He  i. These observations are interpreted using the hydrodynamic and Monte Carlo numerical simulations of various degree of complexity and consistency. At the same time, no attempt has been made to model atmospheric escape of a magnetized HD209458b, to see how the planetary magnetic field might affect the measured transit absorption lines. This paper presents the global 3D MHD self-consistent simulations of the expanding upper atmosphere of HD209458b interacting with the stellar wind, and models the observed H  i (Ly α), O  i (1306 Å), C  ii (1337 Å), and He  i (10 830 Å) transit absorption features. We find that the planetary dipole magnetic field with the equatorial surface value of Bp = 1 G profoundly changes the character of atmospheric material outflow and the related absorption. We also investigate the formation of planetary magnetosphere in the stellar wind and show that its size is more determined by the escaping atmosphere flow rather than by the strength of magnetic field. Fitting of the simulation results to observations enables constraining the stellar XUV flux and He abundance at F XUV ∼ 10 erg cm2 s–1 (at 1 au) and He/H ≈ 0.02, respectively, as well as setting an upper limit for the dipole magnetic field of Bp < 0.1 G on the planetary surface at the equator. This implies that the magnetic dipole moment µP of HD209458b should be less than 6 per cent of the Jovian value. [ABSTRACT FROM AUTHOR]

Possible reasons for the non-detection of absorption in the metastable He  i (23S) line at transit observations of warm Neptune GJ436b, in spite of the well-pronounced strong absorption features measured earlier in Lyα for this planet, are investigated. We perform numeric simulations of the escaping upper atmosphere of this planet and its He  i (23S) triplet absorption with a global 3D multifluid, self-consistent hydrodynamic model. By fitting the model parameters to the lowest detection level of absorption measurements, we constrain an upper limit for the He/H abundance three times smaller than the solar value. We demonstrate that neither the significant changes of the stellar wind related to possible stellar coronal mass ejections (CMEs), or possible variations in the stellar ionization radiation, nor the presence of heavy trace elements have a crucial effect on the absorption at the 10   830 Å line of He  i (23S) triplet. The main reason of weak signature is that the region populated by the absorbing metastable helium is rather small (<3 R p), as well as the small size of the planet itself in comparison to the host star. We show that the radiation pressure force acting on the He  i (23S) atoms spreads them along the line of sight and around the planet, thus further reducing peak absorption. [ABSTRACT FROM AUTHOR]

The results of modeling the Hα absorption spectrum of the atmosphere of the hot Jupiter WASP‑52b are presented. The atmosphere was modeled with a three-dimensional hydrodynamic code. Several different values of the XUV ionizing radiation were considered. The Lyα-photon transfer in the atmosphere was simulated by the Monte Carlo method. Spatial distributions of the volume density of hydrogen atoms excited to the second energy level H(2) were obtained, and absorption spectra in the Hα line were calculated. It was also shown that absorption takes place in a layer with a thickness of about 1.5 times the planetary radius, while the greatest influence on absorption is exerted by Lyα photons produced due to recombination of electrons and protons. [ABSTRACT FROM AUTHOR]

The laboratory experiment on modeling a sub-Alfvénic interaction of expanding plasma cloud with vacuum magnetic field is described. We produce spherically symmetric cloud by 4-beam laser irradiation of the pellet. The presented data reveal complex dynamic of cloud deceleration and formation of two field aligned jets, development of the flute instability and rapid collapse of the diamagnetic cavity. It is shown that cavity collapse can't be explained by plasma motion or anomalous diffusion and requires for explanation a new mechanism. [ABSTRACT FROM AUTHOR]

Structural instabilities that develop during pulsed injection of dense plasma jets into vacuum in the presence of an external quasi-homogeneous magnetic field are studied by high-speed photography using ICCD cameras. The experiments are carried out in the chamber of the "Krot" stand, which has record-breaking dimensions in its class of installations (diameter—3 m, length of the working section—10 m), and makes it possible to study plasma dynamics by various diagnostic methods at scales of more than 1 m both along the magnetic field and in the direction transverse to the magnetic field. During injection along the magnetic field, a transverse collimation of the flow of ionized matter and the development of a flute instability of the plasma boundary are observed, which, at the late stages of expansion, leads to the plasma leaving the injection region in the form of several jets across the field. During transverse injection, the formation of a collimated flow, a "plasma sheet," is observed, in which, as the plasma moves across the field, inhomogeneous structures develop in the direction of injection. [ABSTRACT FROM AUTHOR]

The paper presents the results of laboratory experiment modeling the interaction between Lunar magnetic anomalies and Solar wind. To model the LMA we use quadrupole magnetic field. The main dimensionless parameter of the problem, the ion inertia length relative to the mini-magnetosphere size, well corresponds between experiment and LMA conditions. The main result is measurement of the magnetically reflected proton fluxes, which show qualitative agreement to available satellite data. [ABSTRACT FROM AUTHOR]