Труды сотрудников ИВМ СО РАН

[Text] / H. Gunell [et al.] // Plasma Phys. Control. Fusion. - 2008. - Vol. 50, Is. 7. - Ст. 74018, DOI 10.1088/0741-3335/50/7/074018. - Cited References: 27 . - ISSN 0741-3335РУБ Physics, Fluids & Plasmas + Physics, Nuclear

Аннотация: We present measurements of oscillations in the electron density, ion density and ion velocity in the induced magnetosphere of Mars. The fundamental frequency of the oscillations is a few millihertz, but higher harmonics are present in the spectrum. The oscillations are observed in a region where there is a velocity shear in the plasma flow. The fundamental frequency is in agreement with computational results from an ideal-MHD model. An interpretation based on velocity-shear instabilities is described.


Доп.точки доступа:
Gunell, H.; Amerstorfer, U.V.; Nilsson, H.; Grima, C.; Koepke, M.; Franz, M.; Winningham, J.D.; Frahm, R.A.; Sauvaud, J.A.; Fedorov, A.; Erkaev, N.V.; Еркаев, Николай Васильевич; Biernat, H.K.; Holmstrom, M.; Lundin, R.; Barabash, S.

[Text] / U. V. Amerstorfer [et al.] // Planet Space Sci. - 2007. - Vol. 55, Is. 12. - P1811-1816, DOI 10.1016/j.pss.2007.01.015. - Cited References: 20 . - ISSN 0032-0633РУБ Astronomy & Astrophysics

Аннотация: In this paper, the Kelvin-Helmholtz instability is studied by solving the ideal MHD equations for a compressible plasma. A transition layer of finite thickness between two plasmas, across which the magnitude of the velocity and the density change, is assumed. Growth rates are presented for the transverse case, i.e., the flow velocity is perpendicular to the magnetic field. If only the velocity changes across the boundary layer and the density is kept constant, an important quantity affecting the growth of the Kelvin-Helmholtz instability is the magnetosonic Mach number, which characterizes compressibility. The growth rates for the case when both, the velocity and the density, change are very sensitive to the ratio of the upper plasma density to the lower plasma density: a decrease of the density ratio yields a decrease of the growth rate. Including a density profile is very important for the application of the Kelvin-Helmholtz instability to the solar wind flow around unmagnetized planets, e.g., Venus, where the plasma density increases from the magnetosheath to the ionosphere. (C) 2007 Elsevier Ltd. All rights reserved.


Доп.точки доступа:
Amerstorfer, U.V.; Erkaev, N.V.; Еркаев, Николай Васильевич; Langmayr, D.; Biernat, H.K.

[Text] / N. V. Erkaev [et al.] // Ann. Geophys. - 2007. - Vol. 25, Is. 1. - P145-159. - Cited References: 32 . - ISSN 0992-7689РУБ Astronomy & Astrophysics + Geosciences, Multidisciplinary + Meteorology & Atmospheric Sciences

Аннотация: Mars has no global intrinsic magnetic field, and consequently the solar wind plasma interacts directly with the planetary ionosphere. The main factors of this interaction are: thermalization of plasma after the bow shock, ion pick-up process, and the magnetic barrier effect, which results in the magnetic field enhancement in the vicinity of the obstacle. Results of ideal magnetohydrodynamic and hybrid simulations are compared in the subsolar magnetosheath region. Good agreement between the models is obtained for the magnetic field and plasma parameters just after the shock front, and also for the magnetic field profiles in the magnetosheath. Both models predict similar positions of the proton stoppage boundary, which is known as the ion composition boundary. This comparison allows one to estimate applicability of magnetohydrodynamics for Mars, and also to check the consistency of the hybrid model with Rankine-Hugoniot conditions at the bow shock. An additional effect existing only in the hybrid model is a diffusive penetration of the magnetic field inside the ionosphere. Collisions between ions and neutrals are analyzed as a possible physical reason for the magnetic diffusion seen in the hybrid simulations.


Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Bosswetter, A.; Motschmann, U.; Biernat, H.K.

[Text] / N. V. Erkaev [et al.] // Astrophys. J. Suppl. Ser. - 2005. - Vol. 157, Is. 2. - P396-401, DOI 10.1086/427904. - Cited References: 48 . - ISSN 0067-0049РУБ Astronomy & Astrophysics

Аннотация: During the past years, more than 130 giant planets were discovered in extrasolar planetary systems. Because of the fact that the orbital distances are very close to their host stars, these planets are embedded in a dense stellar wind, which can pick up planetary ions. We model the stellar wind interaction of the short-periodic exoplanets OGLE-TR-56b and HD 209458b at their orbital distances of approximate to 0.023 AU and approximate to 0.045 AU, by calculating the Alfven Mach number and the magnetosonic Mach number in the stellar wind plasma flow. We then analyze the different plasma interaction regimes around the planetary obstacles, which appear for different stellar wind parameters. Our study shows that the stellar wind plasma parameters like temperature, interplanetary magnetic field, particle density, and velocity near planetary obstacles at orbital distances closer than 0.1-0.2 AU have conditions such that no bow shocks evolve. Our study shows also that these close-in exoplanets are in a submagnetosonic regime comparable to the magnetospheric plasma interaction of the inner satellites of Jupiter and Saturn. Furthermore, we compare the results achieved for both exoplanets with the Jupiter-class exoplanet HD 28185b at its orbital distance of approximate to 1.03 AU. Finally, we also discuss the behavior of the stellar wind plasma flow close to the planetary obstacles of two highly eccentric gas giants, namely, HD 108147b and HD 162020b. Because of their eccentric orbits, these two exoplanets periodically experience both regimes with and without a bow shock. Finally, we simulate the neutral gas density of HD 209458b with a Monte Carlo model. By using the plasma parameters obtained in our study we calculate the ion production and loss rate of H+ with a test particle model. Our simulations yield H+ loss rates for HD 209458b or similar giant exoplanets in orders of about 10(8)-10(9) g s(-1). These ion loss rates are at least 1 order of magnitude lower than the observed loss rate of evaporating neutral H atoms. Our study indicates, that similar gas giants at larger orbital distances have lower ion loss rates. Thus, the dominating component of particle loss of short-periodic Jupiter-class exoplanets will be neutral hydrogen.


Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Penz, T.; Lammer, H.; Lichtenegger, H.I.M.; Biernat, H.K.; Wurz, P.; Griessmeier, J.M.; Weiss, W.W.

[Text] / H. Lammer [et al.] // Celest. Mech. Dyn. Astron. - 2005. - Vol. 92, Is. 01.03.2013. - P273-285, DOI 10.1007/s10569-005-0004-4. - Cited References: 27 . - ISSN 0923-2958РУБ Astronomy & Astrophysics + Mathematics, Interdisciplinary Applications

Аннотация: The region around a star where a life-supporting biosphere can evolve is the so-called Habitable Zone (HZ). The current definition of the HZ is based only on the mass-luminosity relation of the star and climatological and meteorological considerations of Earth-like planets, but neglects atmospheric loss processes due to the interaction with the stellar radiation and particle environment. From the knowledge of the planets in the Solar System, we know that planets can only evolve into a habitable world if they have a stable orbit around its host star and if they keep the atmosphere and water inventory during: (i) the period of heavy bombardment by asteroids and comets and (ii) during the host stars' active X-ray and extreme ultraviolet (XUV) and stellar wind periods. Impacts play a minor role for planets with the size and mass like Earth, while high XUV fluxes and strong stellar winds during the active periods of the young host star can destroy the atmospheres and water inventories. We show that XUV produced temperatures in the upper atmospheres of Earth-like planets can lead to hydrodynamic "blow off", resulting in the total loss of the planets water inventory and atmosphere, even if their orbits lie inside the HZ. Further, our study indicates that Earth-like planets inside the HZ of low mass stars may not develop an atmosphere, because at orbital distances closer than 0.3 AU, their atmospheres are highly affected by strong stellar winds and coronal mass ejections (CME's). Our study suggests that planetary magnetospheres will not protect the atmosphere of such planets, because the strong stellar wind of the young star can compress the magnetopause to the atmospheric obstacle. Moreover, planets inside close-in HZ's are tidally locked, therefore, their magnetic moments are weaker than those of an Earth-like planet at 1 AU. Our results indicate that Earth-like planets in orbits of low mass stars may not develop stable biospheres. From this point of view, a HZ, where higher life forms like on Earth may evolve is possibly restricted to higher mass K stars and G stars.


Доп.точки доступа:
Lammer, H.; Kulikov, Y.N.; Penz, T.; Leitner, M.; Biernat, H.K.; Erkaev, N.V.; Еркаев, Николай Васильевич

[Text] / H. . Lammer [et al.] // Astron. Astrophys. - 2009. - Vol. 506, Is. 1. - P399-410, DOI 10.1051/0004-6361/200911922. - Cited References: 46. - The authors thank the anonymous referee for constructive comments and suggestions which helped to improve the paper. H. Lammer, P. Odert, M. Leitzinger, M. L. Khodachenko and A. Hanslmeier gratefully acknowledge the Austrian Fonds zur Forderung der wissenschaftlichen Forschung (FWF grant P19446) for supporting this project. M. Panchenko and M. L. Khodachenko acknowledge also the Austrian Fonds zur Forderung der wissenschaftlichen Forschung (project P20680-N16). H. Lammer, H. I. M. Lichtenegger, H. K. Biernat, Yu. N. Kulikov and N. V. Erkaev thank the AAS "Verwaltungsstelle fur Auslandsbeziehungen" and the RAS. H. Lammer, H. I. M. Lichtenegger, M. L. Khodachenko and Yu. N. Kulikov acknowledge support from the Helmholtz-Gemeinschaft as this research has been supported by the Helmholtz Association through the research alliance "Planetary Evolution and Life". H. Lammer, M. L. Khodachenko, T. Penz, and Yu. N. Kulikov also acknowledge the International Space Science Institute (ISSI; Bern, Switzerland) and the ISSI teams "Evolution of Habitable Planets" and "Evolution of Exoplanet Atmospheres and their Characterization". H. K. Biernat acknowledges additional support due to the Austrian Science Fund under project P20145-N16. The authors also acknowledge fruitful discussions during various meetings related to the Europlanet N2 activities as well as within the N2 Exoplanet discipline working group DWG 7. T. Penz and G. Micela acknowledge support by the Marie Curie Fellowship Contract No. MTKD-CT-2004-002769 of the project "The influence of stellar high radiation on planetary atmospheres". The authors also thank the Austrian Ministry bm:bwk and ASA for funding the CoRoT project. . - ISSN 0004-6361РУБ Astronomy & Astrophysics

Аннотация: Aims. We study the possible atmospheric mass loss from 57 known transiting exoplanets around F, G, K, and M-type stars over evolutionary timescales. For stellar wind induced mass loss studies, we estimate the position of the pressure balance boundary between Coronal Mass Ejection (CME) and stellar wind ram pressures and the planetary ionosphere pressure for non- or weakly magnetized gas giants at close orbits. Methods. The thermal mass loss of atomic hydrogen is calculated by a mass loss equation where we consider a realistic heating efficiency, a radius-scaling law and a mass loss enhancement factor due to stellar tidal forces. The model takes into account the temporal evolution of the stellar EUV flux by applying power laws for F, G, K, and M-type stars. The planetary ionopause obstacle, which is an important factor for ion pick-up escape from non- or weakly magnetized gas giants is estimated by applying empirical power-laws. Results. By assuming a realistic heating efficiency of about 10-25% we found that WASP-12b may have lost about 6-12% of its mass during its lifetime. A few transiting low density gas giants at similar orbital location, like WASP-13b, WASP-15b, CoRoT-1b or CoRoT-5b may have lost up to 1-4% of their initial mass. All other transiting exoplanets in our sample experience negligible thermal loss (<= 1%) during their lifetime. We found that the ionospheric pressure can balance the impinging dense stellar wind and average CME plasma flows at distances which are above the visual radius of "Hot Jupiters", resulting in mass losses <2% over evolutionary timescales. The ram pressure of fast CMEs cannot be balanced by the ionospheric plasma pressure for orbital distances between 0.02-0.1 AU. Therefore, collisions of fast CMEs with hot gas giants should result in large atmospheric losses which may influence the mass evolution of gas giants with masses
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Доп.точки доступа:
Lammer, H.; Odert, P.; Leitzinger, M.; Khodachenko, M.L.; Panchenko, M.; Kulikov, Y.N.; Zhang, T.L.; Lichtenegger, H.I.M.; Erkaev, N.V.; Еркаев, Николай Васильевич; Wuchterl, G.; Micela, G.; Penz, T.; Biernat, H.K.; Weingrill, J.; Steller, M.; Ottacher, H.; Hasiba, J.; Hanslmeier, A.; Austrian Fonds zur Forderung der wissenschaftlichen Forschung [P19446, P20680-N16]; Helmholtz Association; Austrian Science Fund [P20145-N16]; "The influence of stellar high radiation on planetary atmospheres" [MTKD-CT-2004-002769]

[Text] / H. . Lammer [et al.] // Mon. Not. Roy. Astron. Soc. - 2014. - Vol. 439, Is. 4. - P. 3225-3238, DOI 10.1093/mnras/stu085. - Cited References: 75. - The authors acknowledge the support by the FWF NFN project S11601-N16 'Pathways to Habitability: From Disks to Active Stars, Planets and Life', and the related FWF NFN subprojects, S 116 02-N16 'Hydrodynamics in Young Star-Disk Systems', S116 604-N16 'Radiation & Wind Evolution from T Tauri Phase to ZAMS and Beyond', and S116607-N16 'Particle/Radiative Interactions with Upper Atmospheres of Planetary Bodies Under Extreme Stellar Conditions'. KGK, YNK, HL, and PO thank also the Helmholtz Alliance project 'Planetary Evolution and Life'. ML and PO acknowledge support from the FWF project P22950-N16. NVE acknowledges support by the RFBR grant no. 12-05-00152-a. Finally, the authors thank the International Space Science Institute (ISSI) in Bern, and the ISSI team 'Characterizing stellar-and exoplanetary environments'. . - ISSN 0035-8711. - ISSN 1365-2966РУБ Astronomy & Astrophysics

Аннотация: We investigate the origin and loss of captured hydrogen envelopes from protoplanets having masses in a range between 'sub-Earth'-like bodies of 0.1 M-circle plus and 'super-Earths' with 5 M-circle plus in the habitable zone at 1 au of a Sun-like G star, assuming that their rocky cores had formed before the nebula gas dissipated. We model the gravitational attraction and accumulation of nebula gas around a planet's core as a function of protoplanetary luminosity during accretion and calculate the resulting surface temperature by solving the hydrostatic structure equations for the protoplanetary nebula. Depending on nebular properties, such as the dust grain depletion factor, planetesimal accretion rates, and resulting luminosities, for planetary bodies of 0.1-1 M-circle plus we obtain hydrogen envelopes with masses between similar to 2.5 x 10(19) and 1.5 x 10(26) g. For 'super-Earths' with masses between 2 and 5 M-circle plus more massive hydrogen envelopes within the mass range of similar to 7.5 x 10(23)-1.5 x 10(28) g can be captured from the nebula. For studying the escape of these accumulated hydrogen-dominated protoatmospheres, we apply a hydrodynamic upper atmosphere model and calculate the loss rates due to the heating by the high soft-X-ray and extreme ultraviolet (XUV) flux of the young Sun/star. The results of our study indicate that under most nebula conditions 'sub-Earth' and Earth-mass planets can lose their captured hydrogen envelopes by thermal escape during the first similar to 100 Myr after the disc dissipated. However, if a nebula has a low dust depletion factor or low accretion rates resulting in low protoplanetary luminosities, it is possible that even protoplanets with Earth-mass cores may keep their hydrogen envelopes during their whole lifetime. In contrast to lower mass protoplanets, more massive 'super-Earths', which can accumulate a huge amount of nebula gas, lose only tiny fractions of their primordial hydrogen envelopes. Our results agree with the fact that Venus, Earth, and Mars are not surrounded by dense hydrogen envelopes, as well as with the recent discoveries of low density 'super-Earths' that most likely could not get rid of their dense protoatmospheres.

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ИВМ СО РАН

Доп.точки доступа:
Lammer, H.; Stokl, A.; Erkaev, N.V.; Еркаев, Николай Васильевич; Dorfi, E.A.; Odert, P.; Gudel, M.; Kulikov, Y.N.; Kislyakova, K.G.; Leitzinger, M.; FWF NFN [S11601-N16, S 116 02-N16, S116 604-N16, S116607-N16]; FWF [P22950-N16]; RFBR [12-05-00152-a]