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Since the discovery of a potentially low-mass exoplanet around our nearest neighbour star Proxima Centauri, several works have investigated the likelihood of a shielding atmosphere and therefore the potential surface habitability of Proxima Cen b. However, outgassing processes are influenced by several different (unknown) factors such as the actual planet mass, mantle and core composition, and different heating mechanisms in the interior.We aim to identify the critical parameters that influence the mantle and surface evolution of the planet over time, as well as to potentially constrain the time-dependent input of volatiles from mantle into the atmosphere.To study the coupled star-planet evolution, we analyse the heating produced in the interior of Proxima Cen b due to induction heating, which strongly varies with both depth and latitude. We calculate different rotation evolutionary tracks for Proxima Centauri and investigate the change in its rotation period and magnetic field strength. Unlike the Sun, Proxima Centauri possesses a very strong magnetic field of at least a few hundred Gauss, which was likely higher in the past. We apply an interior structure model for varying planet masses (derived from the unknown inclination of observation of the Proxima Centauri system) and iron weight fractions, i.e. different core sizes, in the range of observed Fe-Mg variations in the stellar spectrum. We use a mantle convection model to study the thermal evolution and outgassing efficiency of Proxima Cen b. For unknown planetary parameters such as initial conditions we chose randomly selected values. We take into account heating in the interior due to variable radioactive heat sources and latitute- and radius-dependent induction heating, and compare the heating efficiency to tidal heating.Our results show that induction heating may have been significant in the past, leading to local temperature increases of several hundreds of Kelvin (see Fig. 1). This early heating leads to an earlier depletion of the interior and volatile outgassing compared to if the planet would not have been subject to induction heating. We show that induction heating has an impact comparable to tidal heating when assuming latest estimates on its eccentricity. We furthermore find that the planet mass (linked to the planetary orbital inclination) has a first-order influence on the efficiency of outgassing from the interior. Fig 1: Local induction heating and resulting temperature variations compared to a simulation without induction heating after 1 Gyr of thermal evolution for an example rocky planet of 1.8 Earth masses with an iron content of 20 wt-%.

Self-Consistent 2D modelling of stellar wind interaction with the upper atmosphere of WASP-12b has been performed. The two case-scenarios of the planetary material escape and interaction with the stellar wind, namely the ‘blown by the wind’ (without the inclusion of tidal force) and ‘captured by the star’ (with the tidal force) have been modelled under different stellar XUV radiations and stellar wind parameters. In the first scenario, a shock is formed around the planet, and the planetary mass loss is controlled completely by the stellar radiation energy input. In the second scenario, the mass loss is mainly due to the gravitational interaction effects. The dynamics of MGII and related absorption were modelled with three sets of different stellar wind parameters and XUV flux values.

Thousands of planets outside the Solar system have been discovered, with exoplanets in different environments. Since we cannot expect to find an exoplanetary system fully resembling our Solar System, we consider a Solar System type configuration where the Earth moves in an eccentric orbit. We focus on young Earth 1 billion years ago, when the Sun’s extreme UV (EUV) flux was about 5 times higher than the current radiation. In case of eccentric motion of Earth, strong variations of the EUV flux would influence the evolution of the planet’s atmosphere (EUV radiation of 50 times the current EUV flux would be possible). Taking into account a certain amount of Nitrogen in the atmosphere of such a young Earth, we study the non-thermal loss of N2 over a long time interval. We therefore investigate to what extent eccentric motion will influence the conditions of habitability of a terrestrial planet.

Appearance of microflares in the solar corona during five-minute oscillations in the photosphericconvection rate is considered. Photospheric-convection rate oscillations result in the oscillations of electric current flowing along the loop and the electric-current oscillations in turn lead to generation of inductive electric field which accelerates the particles. Maximum flows of accelerated particles emerge near the apex of the coronal magnetic loop, where the ratio of the accelerating electric field to the Dreicer field is maximal. The heating function due to evaporation of the hot chromospheric plasma, which results from interaction between the accelerated particles and chromospheric bases of the loop is calculated. The microflare energy and the quasi-stationary plasma temperature in a loop as well as the dependence of the latter on the rate amplitude in five-minute photospheric oscillations, are also determined.

In the analysis of low-frequency modulation of the microwave radiation of coronal magnetic loops, we detected modulation whose frequency increases from two to three times just before the beginning of the flare and then decreases to the initial values as the flare proceeds. It is shown that such an effect can be evidence for a sharp increase in the loop current just before the flare process, which leads to the plasma heating and increased energy release. The flute instability can serve as a possible reason for the sharp increase in current.

When studying microwave emission of active regions on the Sun, an effect of parametric resonance between 5-min velocity oscillations in the solar photosphere and sound oscillations of coronal magnetic loops modulating the microwave emission has been discovered for the first time. The effect shows itself as simultaneous excitation in coronal magnetic loop of oscillations with periods 5, 10, and 3 min, which correspond to the pumping frequency, subharmonic, and the first upper frequency of parametric resonance. The parametric resonance can serve as an effective channel of transporting the energy of photospheric oscillations into the upper layers of the solar atmosphere. This effect opens up the important prospects in understanding the mechanisms of coronal plasma heating.

We examined records of the radiation of three flare processes obtained in the Nobeyama observatory in 1992, 2001, and 2003. Observations with the Nobeyama radio heliograph at the frequencies 17 and 34GHz were performed with a sufficient spatial resolution to determine the physical nature of the radiation source. In the first two cases, the radiation source appeared to be a coronal magnetic loop; in the third case, a group of sunspots. In the spectra of the first two events a characteristic modulation was detected, with the frequency that increased by a factor of 2–3 for a fairly short period immediately before the beginning of the flare and later decreased gradually to the initial value. In the spectrum of the event on June 17, 2003 (the radiation source were the sunspots), no modulation of such a type was seen.

Long-periodic (LP) modulations of intensity of Saturnian Kilometric Radiation (SKR) recorded by RPWS instrument onboard Cassini spacecraft were studied by means of a combined data analysis algorithm based on a ”sliding window” Fourier (SWF) procedure and the nonlinearWigner-Ville (WV) method. The analyzed SKR data record covers the years 2004-2005. It has been found that SKR has well pronounced impulsive modulation, with quasi-periodic pulses appeared approximately each 10.74 hours and having duration of about 5 hours. The period of pulses, in spite of the overall stability, has sometimes the disturbances within the interval of 10.74 - 10.76 hours. By this, the whole impulsive modulation of SKR appeared in 2004-2005 in a form of quasi-regularly repeated modulation activity storms. Time interval between the adjacent modulation activity storms most often was within 8-13 days. Altogether, 55 impulsive modulation activity storms were registered during 2004-2005. Besides of the storms of 10.7 h pulses, the intensity of SKR has several more long periodic modulations. In particular, ~6-7 days, ~8-9 days, ~12-13 days and ~25-27 days components were detected. These are connected probably with the quasi-regular character of the storms of 10.74 h pulses. While the origin of 10.74 hour pulses can be associated with the rotation of Saturn, the long periodic modulation features are very likely connected with the detected similar variations of the solar wind parameters. The last in their turn may be caused by the varying solar surface magnetic activity and rotating streams of high speed solar wind. Besides of that, the performed analysis shows that some Saturnian moons may also have influence on the intensity of SKR. In particular, specific modulations with periods corresponding to orbital motions of close moons (Enceladus, Tethys) as well as Titan, Hyperion and Dione were detected.

When studying microwave emission of active regions on the Sun, an effect of parametric resonance between 5-min velocity oscillations in the solar photosphere and sound oscillations of coronal magnetic loops modulating the microwave emission has been discovered for the first time. The effect shows itself as simultaneous excitation in coronal magnetic loop oscillations with periods 5, 10, and 3 min, which correspond to the pumping frequency, subharmonic, and the first upper frequency of parametric resonance. The parametric resonance can serve as an effective channel of transporting the energy of photospheric oscillations into the upper layers of the solar atmosphere. The energy of acoustic waves excited in a coronal magnetic loop, rate of dissipation of acoustic waves, and rate of heating of the coronal plasma are determined. The maximum temperature predicted for the apex of the loop is calculated as a function of velocity of photospheric oscillations, length of the loop, and electric current in the loop. It is shown that the mechanism proposed can explain the origin of quasi-stationary X-ray loops with temperatures of 3-6 MK. The lengths of these loops are resonant for acoustic waves excited by the 5-min photospheric oscillations. The use of the proposed mechanism to explain heating of the X-ray loops expected to be on stars of late spectral types is discussed.

International audience; The discovery of more than 500 exoplanets during the past 15 years has enabled us to characterize the upper atmosphere structure of some exosolar gas giants and to compare observational and modelling results to the known planets in the Solar System. It is of great interest to understand if these exosolar "Hot Jupiters" share similar physical processes compared to the giant planets (Jupiter and Saturn) in the Solar System with regard to their magnetic dynamos and the corresponding expected magnetic field strengths. In this work we discuss how observations of stellar Lyman-alpha absorption by so-called Energetic Neutral Atoms (ENAs) around transiting exoplanets together with theoretical modelling efforts can be used as a tool for estimating magnetic obstacle sizes and the corresponding magnetic field strength. For demonstrating this method we model the production of stellar wind related planetary hydrogen and ENA populations around the exosolar gas giant HD 209458b and show how a detailed analysis of attenuation spectra obtained during transits can be used for the estimation of the planet's magnetic obstacle size and hence its dynamo field strength. Our study indicates that the magnetic field strength of HD 209458b which is able to balance the stellar wind plasma flow by a magnetic obstacle around the planet which can explain the observed Lyman-alpha line profiles observed before and during the transits by HST corresponds to a magnetic dipole moment which is about 40 percent of Jupiters value.