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/ C. J. Farrugia [et al.] // Sol. Phys. - 2012. - Vol. 281, Is. 1. - pp. 461-489, DOI 10.1007/s11207-012-0119-1. - Cited References: 53 . - 29. - ISSN 0038-0938РУБ Astronomy & Astrophysics

Аннотация: We discuss the temporal variations and frequency distributions of solar wind and interplanetary magnetic field parameters during the solar minimum of 2007-2009 from measurements returned by the IMPACT and PLASTIC instruments on STEREO-A. We find that the density and total field strength were significantly weaker than in the previous minimum. The Alfv,n Mach number was higher than typical. This reflects the weakness of magnetohydrodynamic (MHD) forces, and has a direct effect on the solar wind-magnetosphere interactions. We then discuss two major aspects that this weak solar activity had on the magnetosphere, using data from Wind and ground-based observations: i) the dayside contribution to the cross-polar cap potential (CPCP), and ii) the shapes of the magnetopause and bow shock. For i) we find a low interplanetary electric field of 1.3 +/- 0.9 mV m(-1) and a CPCP of 37.3 +/- 20.2 kV. The auroral activity is closely correlated to the prevalent stream-stream interactions. We suggest that the Alfven wave trains in the fast streams and Kelvin-Helmholtz instability were the predominant agents mediating the transfer of solar wind momentum and energy to the magnetosphere during this three-year period. For ii) we determine 328 magnetopause and 271 bow shock crossings made by Geotail, Cluster 1, and the THEMIS B and C spacecraft during a three-month interval when the daily averages of the magnetic and kinetic energy densities attained their lowest value during the three years under survey. We use the same numerical approach as in Fairfield's (J. Geophys. Res. 76, 7600, 1971) empirical model and compare our findings with three magnetopause models. The stand-off distance of the subsolar magnetopause and bow shock were 11.8 R-E and 14.35 R-E, respectively. When comparing with Fairfield's (1971) classic result, we find that the subsolar magnetosheath is thinner by similar to 1 R-E. This is mainly due to the low dynamic pressure which results in a sunward shift of the magnetopause. The magnetopause is more flared than in Fairfield's model. By contrast the bow shock is less flared, and the latter is the result of weaker MHD forces.

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Farrugia, C.J.; Harris, B.; Leitner, M.; Mostl, C.; Galvin, A.B.; Simunac, K.D.C.; Torbert, R.B.; Temmer, M.B.; Veronig, A.M.; Erkaev, N.V.; Еркаев, Николай Васильевич; Szabo, A.; Ogilvie, K.W.; Luhmann, J.G.; Osherovich, V.A.

[Text] / N. V. Erkaev [et al.] // Astrobiology. - 2013. - Vol. 13, Is. 11. - P1011-1029, DOI 10.1089/ast.2012.0957. - Cited References: 92. - M. Gudel, K. G. Kislyakova, M. L. Khodachenko, and H. Lammer acknowledge support by the FWF NFN project S116 601-N16 "Pathways to Habitability: From Disks to Active Stars, Planets and Life" and the related FWF NFN subprojects S116 604-N16 "Radiation & Wind Evolution from T Tauri Phase to ZAMS and Beyond," S116 606-N16 "Magnetospheric Electrodynamics of Exoplanets," S116 607-N16 "Particle/Radiative Interactions with Upper Atmospheres of Planetary Bodies under Extreme Stellar Conditions." K. G. Kislyakova, Yu. N. Kulikov, H. Lammer, and P. Odert thank also the Helmholtz Alliance project "Planetary Evolution and Life." P. Odert and A. Hanslmeier also acknowledge support from the FWF project P22950-N16. The authors also acknowledge support from the EU FP7 project IMPEx (No. 262863) and the EUROPLANET-RI projects, JRA3/EMDAF and the Na2 science WG5. The authors thank the International Space Science Institute (ISSI) in Bern and the ISSI team "Characterizing stellar and exoplanetary environments." N. V. Erkaev acknowledges support by the RFBR grant No 12-05-00152-a. Finally, the authors thank referee Tian Feng, from the Tsinghua University, Beijing, China, for suggestions and recommendations that helped to improve the work. . - 19. - ISSN 1531-1074РУБ Astronomy & Astrophysics + Biology + Geosciences, Multidisciplinary

Аннотация: The recently discovered low-density super-Earths Kepler-11b, Kepler-11f, Kepler-11d, Kepler-11e, and planets such as GJ 1214b represent the most likely known planets that are surrounded by dense H/He envelopes or contain deep H2O oceans also surrounded by dense hydrogen envelopes. Although these super-Earths are orbiting relatively close to their host stars, they have not lost their captured nebula-based hydrogen-rich or degassed volatile-rich steam protoatmospheres. Thus, it is interesting to estimate the maximum possible amount of atmospheric hydrogen loss from a terrestrial planet orbiting within the habitable zone of late main sequence host stars. For studying the thermosphere structure and escape, we apply a 1-D hydrodynamic upper atmosphere model that solves the equations of mass, momentum, and energy conservation for a planet with the mass and size of Earth and for a super-Earth with a size of 2 R-Earth and a mass of 10 M-Earth. We calculate volume heating rates by the stellar soft X-ray and extreme ultraviolet radiation (XUV) and expansion of the upper atmosphere, its temperature, density, and velocity structure and related thermal escape rates during the planet's lifetime. Moreover, we investigate under which conditions both planets enter the blow-off escape regime and may therefore experience loss rates that are close to the energy-limited escape. Finally, we discuss the results in the context of atmospheric evolution and implications for habitability of terrestrial planets in general. Key Words: Stellar activityLow-mass starsEarly atmospheresEarth-like exoplanetsEnergetic neutral atomsIon escapeHabitability. Astrobiology 13, 1011-1029.

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Держатели документа:
[Erkaev, Nikolai V.] Russian Acad Sci, Siberian Div, Inst Computat Modelling, Krasnoyarsk 660036, Russia
[Erkaev, Nikolai V.] Siberian Fed Univ, Krasnoyarsk, Russia
[Lammer, Helmut
Odert, Petra
Kislyakova, Kristina G.
Khodachenko, Maxim L.
Biernat, Helfried] Austrian Acad Sci, Space Res Inst, A-8010 Graz, Austria
[Odert, Petra
Kislyakova, Kristina G.
Hanslmeier, Arnold] Graz Univ, Inst Phys, Graz, Austria
[Kulikov, Yuri N.] Russian Acad Sci, Polar Geophys Inst, Murmansk, Russia
[Khodachenko, Maxim L.] Moscow MV Lomonosov State Univ, Inst Nucl Phys, Moscow, Russia
[Guedel, Manuel] Univ Vienna, Inst Astrophys, A-1010 Vienna, Austria
ИВМ СО РАН

Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Lammer, H.; Odert, P.; Kulikov, Y.N.; Kislyakova, K.G.; Khodachenko, M.L.; Gudel, M.; Hanslmeier, A.; Biernat, H.K.; FWF NFN project [S116 601-N16, S116 604-N16, S116 606-N16, S116 607-N16]; FWF project [P22950-N16]; EU [262863]; EUROPLANET-RI projects; JRA3/EMDAF; Na2 science WG5; RFBR [12-05-00152-a]

[Text] / C. J. Farrugia [et al.] // J. Geophys. Res-Space Phys. - 2008. - Vol. 113. - Ст. A00B01, DOI 10.1029/2007JA012953. - Cited References: 38 . - ISSN 0148-0227РУБ Astronomy & Astrophysics

Аннотация: We identify a planar, pressure-balanced structure bounded by sharp changes in the dynamic pressure plastered against the front boundary of the magnetic cloud which passed Earth on 20 November 2003. The front boundary of the magnetic cloud (MC) is particularly well-defined in this case, being located where the He(++)/H(+) number density ratio jumps from 4 to 10% for the first time and the proton plasma beta decreases sharply from similar to 1 to similar to 0.001. The feature, estimated to have a length scale similar to 50 RE in the Sun-Earth direction, bears close resemblance to a slow mode transition region in that the magnetic pressure decreases, the plasma pressure increases, and their temporal variations are anticorrelated. Using a 2-D MHD simulation, we hypothesize that a pressure-balanced structure was encountered by the MC en route to Earth. Our calculations reproduce qualitatively the major features of the observations. Using a simplified geometry suggested by the observations, we find that the lateral deflection speed of the plasma is less than the lateral expansion speed of the MC. We infer that the structure traversed the MC sheath in similar to 20 h, consistent with its crossing of the MC's shock at 0.6-0.7 AU. The finding is consistent with the recent paradigm according to which solar wind plasma and magnetic field tend to pile up in front of interplanetary ejecta because the expansion of the ejecta hinders the shocked solar wind plasma from deflecting effectively around the object. Also, the inferred "age'' of the layer contiguous to the surface of the MC, the earliest relic of its passage through the inner heliosphere, is in agreement with general estimates.


Доп.точки доступа:
Farrugia, C.J.; Erkaev, N.V.; Еркаев, Николай Васильевич; Taubenschuss, U.; Shaidurov, V.A.; Smith, C.W.; Biernat, H.K.

[Text] / N. V. Erkaev [et al.] // Astron. Astrophys. - 2007. - Vol. 472, Is. 1. - P329-334, DOI 10.1051/0004-6361:20066929. - Cited References: 26 . - ISSN 0004-6361РУБ Astronomy & Astrophysics

Аннотация: Context. A study of the mass loss enhancement for very close "Hot Jupiters" due to the gravitational field of the host star is presented. Aims. The influence of the proximity to a planet of the Roche lobe boundary on the critical temperature for blow-off conditions for estimating the increase of the mass loss rate through hydrodynamic blow-off for close-in exoplanets is investigated. Methods. We consider the gravitational potential for a star and a planet along the line that joins their mass centers and the energy balance equation for an evaporating planetary atmosphere including the effect of the stellar tidal force on atmospheric escape. Results. By studying the effect of the Roche lobe on the atmospheric loss from short-periodic gas giants we derived reasonably accurate approximate formulas to estimate atmospheric loss enhancement due to the action of tidal forces on a "Hot Jupiter" and to calculate the critical temperature for the onset of "geometrical blow-off", which are valid for any physical values of the Roche lobe radial distance. Using these formulas, we found that the stellar tidal forces can enhance the hydrodynamic evaporation rate from TreS-1 and OGLE-TR-56b by about 2 fold, while for HD 209458b we found an enhancement of about 50%. For similar exoplanets which are closer to their host star than OGLE-TR-56b, the mass loss enhancement can be even larger. Moreover, we showed that the effect of the Roche lobe allows "Hot Jupiters" to reach blow-off conditions at temperatures which are less than expected due to the stellar X-ray and EUV heating.


Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Kulikov, Y.N.; Lammer, H.; Selsis, F.; Langmayr, D.; Jaritz, G.F.; Biernat, H.K.

[Text] / M. L. Khodachenko [et al.] // Planet Space Sci. - 2007. - Vol. 55: Symposium on Exoplanets and Planetary Formation (APR 25-30, 2004, Nice, FRANCE), Is. 5. - P631-642, DOI 10.1016/j.pss.2006.07.010. - Cited References: 63 . - ISSN 0032-0633РУБ Astronomy & Astrophysics

Аннотация: Atmospheric erosion due to CME-caused ion pick-up is investigated here for the first time for short periodic gas giants (so-called "Hot Jupiters") orbiting close to a star, To study the effect of encountering CMEs produced on the inagnetospheres and atmospheres of "Hot Jupiters" we model possible interaction of dense CME plasma with the exoplanet HD209458b (r(pl) = 1.43r(Jup) M(pl) = 0.69 M(jup)), which orbits a 4.0-5.0 Gyr old Sun-like star at a distance of about 0.045 AU. A numerical hydrodynamic model is applied for calculation of the upper atmospheric density and the hydrogen wind of HD209458b Lis a function of planetocentric distance. Taking into account the similarity of HD209458b's host star to Our Sun we use for the study of the ion production and loss rate of H(+) ions the solar CME plasma parameters and apply a numerical test particle model. Tidal-locking of short periodic exoplanets closely located to their host stars should result in weaker intrinsic planetary magnetic moments, as compared to those of the fast rotating Jupiter type planets at much larger orbits. It is shown that in this case the encountering CME plasma can compress the magnetospheric stand-off distance of short periodic "Hot Jupiters" down to the heights Lit which the ionization and pick-LIP of the planetary neutral atmosphere by the CME plasma flow take place. Assuming for the host star of HD209458b the same CME occurrence rate Lis on the Suit, we estimate possible total mass loss rates of HD2094581b due to its collisions with CMEs over the planet lifetime. It has been found that Under different estimations of the value of a planetary magnetic moment, HD209458b Could have lost over its lifetime the mass from 0-2 up to several times of its present mass M(pl). (c) 2006 Elsevier Ltd. All rights reserved.


Доп.точки доступа:
Khodachenko, M.L.; Lammer, H.; Lichtenegger, H.I.M.; Langmayr, D.; Erkaev, N.V.; Еркаев, Николай Васильевич; Griessmeier, J.M.; Leitner, M.; Penz, T.; Biernat, H.K.; Motschmann, U.; Rucker, H.O.

[Text] / G. F. Jaritz [et al.] // Astron. Astrophys. - 2005. - Vol. 439, Is. 2. - P771-775, DOI 10.1051/0004-6361:20052946. - Cited References: 32 . - ISSN 0004-6361РУБ Astronomy & Astrophysics

Аннотация: Theoretical studies and recent observational evidence of the expansion of the atmospheres of short-periodic exoplanets show that the atmospheres extend up to several planetary radii. This indicates that the atmospheres experience blow-off conditions. Because of the short orbital distance to their host stars, the expansion of the upper atmosphere is no longer radially symmetric, but depends on the direction to the central body, resulting in a deformation of the expanded atmosphere. We show the connection between atmospheric expansion, tidal forces and effects of the Roche potential and find that HD209458 b, OGLE-TR-10 b and OGLE-TR-111 b are most likely in a state of classical hydrodynamical blow-off because the distance where blow-off can occur is less than the distance to the Lagrangian point L1. On the other hand, OGLE-TR-56 b, OGLE-TR-113 b, OGLE-TR-132 b and TreS-1 experience a geometrical blow-off defined by the Roche lobe as proposed by Lecavelier des Etangs et al. (2004, A&A, 418, L1). Our results have important implications for the evolution of short periodic gas giants, because the Roche lobe overflow of the atmosphere can lead to lower mass loss rates over the exoplanets history, compared to gas giants which experience hydrodynamic expansion and loss unaffected by this boundary. Thus, massive exoplanets like OGLE-TR-56 b in very close orbital distances are subject to geometrical blow-off conditions, this results in a total mass loss for this particular exoplanet of the order of about 3 x 10(-2) M-pl over the planets age, even if current mass loss rates of about 2 x 10(11) g s(-1) are calculated. If the exoplanet effected by the geometrical blow-off is more massive, the mass loss rate is even lower. However, giant exoplanets like HD209458 b, OGLE-TR-10 b and OGLE-TR-111 b at orbital distances of about 0.05 AU may experience classical hydrodynamic blow-off conditions, which can result in higher mass loss rates. Thus, such planets may shrink to their core sizes during the X-ray and EUV active periods of their host stars as proposed by Lammer et al. ( 2003, ApJ, L121, 598) and Bara. e et al. (2004, A& A, 419, L13).


Доп.точки доступа:
Jaritz, G.F.; Endler, S.; Langmayr, D.; Lammer, H.; Griessmeier, J.M.; Erkaev, N.V.; Еркаев, Николай Васильевич; 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]

/ M. G. Sadovsky, M. Y. Senashova, A. V. Malyshev // BMC Bioinformatics. - 2020. - Vol. 21. - Ст. 83, DOI 10.1186/s12859-020-3350-z. - Cited References:45 . - ISSN 1471-2105РУБ Biochemical Research Methods + Biotechnology & Applied Microbiology

Аннотация: Background Previously, a seven-cluster pattern claiming to be a universal one in bacterial genomes has been reported. Keeping in mind the most popular theory of chloroplast origin, we checked whether a similar pattern is observed in chloroplast genomes. Results Surprisingly, eight cluster structure has been found, for chloroplasts. The pattern observed for chloroplasts differs rather significantly, from bacterial one, and from that latter observed for cyanobacteria. The structure is provided by clustering of the fragments of equal length isolated within a genome so that each fragment is converted in triplet frequency dictionary with non-overlapping triplets with no gaps in frame tiling. The points in 63-dimensional space were clustered due to elastic map technique. The eight cluster found in chloroplasts comprises the fragments of a genome bearing tRNA genes and exhibiting excessively high GC-content, in comparison to the entire genome. Conclusion Chloroplasts exhibit very specific symmetry type in distribution of coding and non-coding fragments of a genome in the space of triplet frequencies: this is mirror symmetry. Cyanobacteria may have both mirror symmetry, and the rotational symmetry typical for other bacteria.

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Держатели документа:
RAS, SB, Inst Computat Modelling, Krasnoyarsk 660036, Russia.
Siberian Fed Univ, Svobodny Prosp 79, Krasnoyarsk 660041, Russia.
VF Voino Yasenetsky Krasnoyarsk State Med Univ, P Zheleznjaka Str 1, Krasnoyarsk 660022, Russia.

Доп.точки доступа:
Sadovsky, Michael G.; Senashova, Maria Yu; Malyshev, Andrew V.