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ABSTRACT: The recently discovered low-density "super-Earths" Kepler-11b, Kepler-11f,
Kepler-11d, Kepler-11e, and planets such as GJ 1214b represent most likely
planets which 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 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 a Sun-like
G-type host star. For studying the thermosphere structure and escape we apply a
1-D hydrodynamic upper atmosphere model which solves the equations of mass,
momentum and energy conservation for a planet with the mass and size of the
Earth and for a "super-Earth" with a size of 2 R_Earth and a mass of 10
M_Earth. We calculate heating rates by the stellar soft X-rays and EUV
radiation and expansion of the upper atmosphere, its temperature, density and
velocity structure and related thermal escape rates during planet's life time.
Moreover, we investigate under which conditions both planets enter the blow-off
escape regime and may therefore experience loss rates which 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.
12/2012;
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K. G. Kislyakova, H. Lammer,
M. Holmström,
M. Panchenko,
P. Odert,
N. V. Erkaev,
M. Leitzinger,
M. L. Khodachenko,
Yu. N. Kulikov,
M. Güdel,
A. Hanslmeier
[show abstract]
[hide abstract]
ABSTRACT: The interactions between the stellar wind plasma flow of a typical M star
such as GJ 436 and hydrogen-rich upper atmospheres of an Earth-like planet and
a "super-Earth" with the radius of 2 R_Earth and a mass of 10 M_Earth, located
within the habitable zone at ~0.24 AU are studied. The formation of extended
atomic hydrogen coronae under the influence of such factors as the stellar XUV
flux (soft X-rays and EUV), stellar wind density and velocity, shape of a
planetary obstacle (e.g., magnetosphere, ionopause) and the heating efficiency
on the evolution of the hydrogen-rich upper atmospheres is investigated. XUV
fluxes which are 1, 10, 50 and 100 times higher compared to that of the present
Sun are considered and the formation of the high-energy neutral hydrogen clouds
around the planets due to charge-exchange reaction under various stellar
conditions have been modeled. Charge-exchange between stellar wind protons with
the planetary hydrogen atoms and photoionization leads to the production of
initially cold ions of planetary origin. Depending on the stellar wind
conditions and the assumed XUV exposure of the upper atmosphere we found that
the ion production rates for the studied planets can vary over a wide range
from ~1.0x10^{25} s^{-1} to ~5.3x10^{30} s^{-1}. Our findings indicate that
most likely the majority of these planetary ions are picked up by the stellar
wind and lost from the planet. The estimations of the long-time non-thermal
escape for these planets are obtained and compared with the thermal ones.
According to our estimates, non-thermal escape of ionized hydrogen atoms over a
planet's lifetime varies between ~0.4 Earth ocean equivalent amounts of
hydrogen (EO_H) to < 3 EO_H and usually is several times smaller in comparison
to the thermal atmospheric escape.
12/2012;
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[hide abstract]
ABSTRACT: HST transit observations in the near-UV performed in 2009 made WASP-12b one
of the most "mysterious" exoplanets; the system presents an early-ingress,
which can be explained by the presence of optically thick matter located ahead
of the planet at a distance of 4-5 planet radii. This work follows previous
attempts to explain this asymmetry with an exospheric outflow or a bow shock,
induced by a planetary magnetic field, and provides a numerical solution of the
early-ingress, though we did not perform any radiative transfer calculation. We
performed pure 3D gas dynamic simulations of the plasma interaction between
WASP-12b and its host star, and describe the flow pattern in the system. In
particular, we show that the overfilling of the planet's Roche lobe leads to a
noticeable outflow from the upper atmosphere in the direction of the L1 and L2
points. Due to the conservation of the angular momentum, the flow to the L1
point is deflected in the direction of the planet's orbital motion, while the
flow towards L2 is deflected in the opposite direction, resulting in a
non-axisymmetric envelope, surrounding the planet. The supersonic motion of the
planet inside the stellar wind leads to the formation of a bow shock with a
complex shape. The existence of the bow shock slows down the outflow through
the L1 and L2 points, allowing us to consider a long-living flow structure
which is in the steady-state.
12/2012;
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[show abstract]
[hide abstract]
ABSTRACT: The discovery of transiting "super-Earths" with inflated radii and known
masses such as Kepler-11b-f, GJ 1214b and 55 Cnc e, indicates that these
exoplanets did not lose their nebula-captured hydrogen-rich, degassed or
impact-delivered protoatmospheres by atmospheric escape processes. Because
hydrodynamic blow-off of atmospheric hydrogen atoms is the most efficient
atmospheric escape process we apply a time-dependent numerical algorithm which
is able to solve the system of 1-D fluid equations for mass, momentum, and
energy conservation to investigate the criteria under which "super-Earths" with
hydrogen-dominated upper atmospheres can experience hydrodynamic expansion by
heating of the stellar XUV (soft X-rays and extreme ultraviolet) radiation and
thermal escape via blow-off. Depending on orbit location, XUV flux, heating
efficiency and the planet's mean density our results indicate that the upper
atmospheres of all "super-Earths" can expand to large distances, so that
besides of Kepler-11c all of them experience atmospheric mass-loss due to Roche
lobe overflow. The atmospheric mass-loss of the studied "super-Earths" is one
to two orders of magnitude lower compared to that of "hot Jupiters" such as HD
209458b, so that one can expect that these exoplanets cannot lose their
hydrogen-envelopes during their remaining lifetimes.
10/2012;
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Planetary and Space Science 05/2012; 00(00):00. · 2.22 Impact Factor
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H. Lammer,
R. Dvorak,
M. Deleuil,
P. Barge,
H. J. Deeg,
C. Moutou,
A. Erikson,
Sz. Csizmadia,
B. Tingley,
H. Bruntt, [......],
D. Rouan,
B. Samuel,
J. Schneider,
A. Shporer,
B. Stecklum,
M. Steller,
R. Street,
S. Udry,
J. Weingrill,
G. Wuchterl
Solar System Research 05/2012; 45(4):374-375. · 0.68 Impact Factor
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M Ollivier,
M Gillon,
A Santerne,
G Wuchterl,
M Havel,
H Bruntt,
P Bordé,
T Pasternacki,
M Endl,
D Gandolfi, [......],
M Pätzold,
D Queloz,
H Rauer,
D Rouan,
B Samuel,
J Schneider,
M Tadeu dos Santos,
L Tal-Or,
B Tingley,
J Weingrill
åp. 05/2012; 541:A149.
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ABSTRACT: During the previous years spacecraft observations of so-called Energetic Neutral Atoms (ENAs) have become an important remote-sensing
technique in planetary science for analyzing the solar wind plasma flow around the upper atmospheric environments of Solar
System bodies. ENAs are produced whenever solar- or stellar wind protons interact via charge exchange with a neutral particle
from a planetary atmosphere so that their signals constrain both, ion distributions and neutral gas densities. The observation
of ENAs which have been generated due to charge exchange with stellar wind plasma have been used for the indirect mass loss
and stellar wind property estimation of Sun-like stars by observing the interaction regions carved out by the collisions between
stellar winds and the interstellar medium. In this work we review ENA-observations and data interpretations at Solar System
planets and recent hydrogen-cloud observations in UV Lyman-α absorption around hydrogen-rich extra-solar gas giants. We discuss the production of stellar wind related hydrogen ENA-clouds
around close-in exoplanets and show how a detailed analysis of attenuation spectra obtained for transiting hydrogen-rich close-in
gas giants can be used for the study of the upper atmosphere structure, the planet’s magnetosphere and to obtain information
on stellar wind properties. Finally, we discuss how future hydrogen cloud observations around exoplanets by space observatories
like the Russia-led World Space Observatory-UV (WSO-UV) together with ESAs planned PLATO mission can be used for the reconstruction
of the solar wind history or the test of magnetosphere evolution hypotheses.
KeywordsENAs–Hydrogen coronae–“Hot Jupiters”–Transits–Star-exoplanet interaction–Magnetospheres–Stellar wind–PLATO–WSO-UV
Astrophysics and Space Science 04/2012; 335(1):9-23. · 1.69 Impact Factor
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[show abstract]
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ABSTRACT: Calculation results on the possible influence of the hot oxygen fraction on the satellite drag in the Earth’s upper atmosphere
on the basis of the previously developed theoretical model of the hot oxygen geocorona are presented. Calculations have shown
that for satellites with orbits above 500 km, the contribution from the corona is extremely important. Even for the energy
flux Q
0 = 1 erg cm−2 s−1, the contribution of the hot oxygen can reach tens of percent; and considering that real energy fluxes are usually higher,
one can suggest that for extreme solar events, the contribution of hot oxygen to the atmospheric drag of the satellite will
be dominant. For lower altitudes, the contribution of hot oxygen is, to a considerable degree, defined by the solar activity
level. The calculations imply that for the daytime polar atmosphere, the change of the solar activity level from F
10.7 ∼ 200 to F
10.7 ∼ 70 leads to an increase in the ratio of the hot oxygen partial pressure to the thermal oxygen partial pressure by a factor
of almost 30, from 0.85 to 25%. The transition from daytime conditions to nighttime conditions almost does not change the
contribution from suprathermal particles. The decrease of the characteristic energy of precipitating particles, i.e., for
the case of charged particles with a softer energy spectrum, leads to a noticeable increase of the contribution of the suprathermal
fraction, by a factor of 1.5–2. It has been ascertained that electrons make the main contribution to the formation of the
suprathermal fraction; and with the increase of the energy of precipitating electrons, the contribution of hot oxygen to the
satellite drag also increases proportionally. Thus, for a typical burst, the contribution of the suprathermal fraction is
30% even at relatively high solar activity F
10.7 = 135.
Solar System Research 04/2012; 45(3):231-239. · 0.68 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The results of numerical simulation of the general circulation in the Titan’s atmosphere at heights from 0 to 250 km are presented,
obtained using a new model based on numerical solution of complete equations of motion of viscous compressible gas at the
temperature distribution given by an empirical model. The model uses no hydrostatic equation and, as compared with traditional
models, has higher resolution in vertical and over horizon. The results presented differ from results of other models and
agree with the vertical profile of the zonal component of wind velocity measured by the Huygens spacecraft. Interpretation of this profile is given, including its main peculiarity consisting in a nonmonotonic behavior
at heights from 60 to 75 km.
Cosmic Research 04/2012; 47(2):114-125. · 0.39 Impact Factor
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H. Lammer,
A. Hanslmeier,
J. Schneider,
I. K. Stateva,
M. Barthelemy,
A. Belu,
D. Bisikalo,
M. Bonavita,
V. Eybl,
V. Coudé du Foresto, [......],
E. Palle,
A. Reiners,
I. Ribas,
H. O. Rucker,
N. Sarda,
J. Seckbach,
V. I. Shematovich,
A. Sozzetti,
A. Tavrov,
M. Xiang-Grüß
[show abstract]
[hide abstract]
ABSTRACT: After the discovery of more than 400 planets beyond our Solar System, the characterization of exoplanets as well as their host stars can be considered as one of the fastest growing fields in space science during the past decade. The characterization of exoplanets can only be carried out in a well coordinated interdisciplinary way which connects planetary science, solar/stellar physics and astrophysics. We present a status report on the characterization of exoplanets and their host stars by reviewing the relevant space- and ground-based projects. One finds that the previous strategy changed from space mission concepts which were designed to search, find and characterize Earth-like rocky exoplanets to: A statistical study of planetary objects in order to get information about their abundance, an identification of potential target and finally its analysis. Spectral analysis of exoplanets is mandatory, particularly to identify bio-signatures on Earth-like planets. Direct characterization of exoplanets should be done by spectroscopy, both in the visible and in the infrared spectral range. The way leading to the direct detection and characterization of exoplanets is then paved by several questions, either concerning the pre-required science or the associated observational strategy.
Solar System Research 04/2012; 44(4):290-310. · 0.68 Impact Factor
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H. Lammer,
V. Eybl,
K. G. Kislyakova,
J. Weingrill,
M. Holmström,
M. L. Khodachenko,
Yu. N. Kulikov,
A. Reiners,
M. Leitzinger,
P. Odert,
M. Xiang Grüß,
B. Dorner,
M. Güdel,
A. Hanslmeier
[show abstract]
[hide abstract]
ABSTRACT: The detection and investigation of EUV heated, extended and non-hydrostatic upper atmospheres around terrestrial exoplanets would provide important insights into the interaction of the host stars plasma environment as well as the evolution of Earth-type
planets their atmospheres and possible magnetic environments. We discuss different scenarios where one can expect that Earth-like planets should experience non-hydrostatic upper atmosphere conditions so that dynamically outward flowing neutral atoms can
interact with the stellar plasma flow so that huge hydrogen coronae and energetic neutral atoms (ENA) can be produced via charge exchange. By observing the size of the extended upper atmospheres and related ENA-clouds and by determining the velocities of the surrounding hydrogen atoms, conclusions can be drawn in respect to the origin of these features. Due to the large number of M-type stars in our neighbourhood and their long periods of strong and moderate stellar activity in comparison to G-stars, we expect that M-type stars represent the most promising candidates for the detection of hydrogen ENA-clouds and the subsequent study of the interaction between the host star and the planets’ upper atmosphere. We show that the low mass of M-type stars also makes them preferable targets to observe extended hydrogen clouds around terrestrial exoplanets with a mass as low as one Earth mass. Transit follow-up observations in the UV-range of terrestrial exoplanets around M-type stars with space observatories such as the World Space Observatory-UV (WSO-UV) would provide a unique opportunity to shed more light on the early evolution of Earth-like planets, including those of our own Solar System.
KeywordsM star planets–Expanded atmospheres–ENAs–Hydrogen-clouds–Habitability–WSO-UV
Astrophysics and Space Science 04/2012; 335(1):39-50. · 1.69 Impact Factor
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A. Coustenis,
S. K. Atreya,
T. Balint,
R. H. Brown,
M. K. Dougherty,
F. Ferri,
M. Fulchignoni,
D. Gautier,
R. A. Gowen,
C. A. Griffith, [......],
C. Szopa,
R. Thissen,
M. G. Tomasko,
D. Toublanc,
H. Vali,
I. Vardavas,
V. Vuitton,
R. A. West,
R. Yelle,
E. F. Young
[show abstract]
[hide abstract]
ABSTRACT: TandEM was proposed as an L-class (large) mission in response to ESA’s Cosmic Vision 2015–2025 Call, and accepted for further
studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds
tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini–Huygens
mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM
is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is
designed to build on but exceed the scientific and technological accomplishments of the Cassini–Huygens mission, exploring
Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time).
In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft
would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators
to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in
situ investigation components, i.e. a hot-air balloon (Montgolfière) and possibly several landing probes to be delivered through
the atmosphere.
Experimental Astronomy 04/2012; 23(3):893-946. · 1.82 Impact Factor
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H Lammer,
Manuel Güdel,
Y Kulikov,
I. Ribas,
T Zaqarashvili,
M Khodachenko,
K Kislyakova,
H Gröller,
P. Odert,
M. Leitzinger, [......],
S Krauss,
W Hausleitner,
M Holmström,
J Sanz-Forcada,
H. Lichtenegger,
A. Hanslmaier,
V Shematovich,
D Bisikalo,
Heike Rauer,
M Fridlund
[show abstract]
[hide abstract]
ABSTRACT: It is shown that the evolution of planetary atmospheres can only be understood if one recognizes the fact that the radiation and particle environment of the Sun or a planet’s host star were not always on the same level as at present. New insights and the latest observations and research regarding the evolution of the solar radiation, plasma environment and solar/stellar magnetic field derived from the observations of solar proxies with different ages will be given. We show that the extreme radiation and plasma environments of the young Sun/stars have important implications for the evolution of planetary atmospheres and may be responsible for the fact that planets with low gravity like early Mars most likely never build up a dense atmosphere during the first few 100 Myr after their origin. Finally we present an innovative new idea on how hydrogen clouds and energetic neutral atom (ENA) observations around transiting Earth-like exoplanets by space observatories such as the WSO-UV, can be used for validating the addressed atmospheric evolution studies. Such observations would enhance our understanding
on the impact on the activity of the young Sun on the early atmospheres of Venus, Earth, Mars and other Solar System bodies as well as exoplanets.
Earth Planets and Space 03/2012; 64(Special issue: Comparative Studies of the Plasma at Non-magnetized Planets/Moons):179-199. · 0.80 Impact Factor
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M. Deleuil,
A. S. Bonomo,
S. Ferraz-Mello,
A. Erikson,
F. Bouchy,
M. Havel,
S. Aigrain,
J.-M. Almenara,
R. Alonso,
M. Auvergne, [......],
D. Queloz,
H. Rauer,
A. Rodríguez,
D. Rouan,
A. Santerne,
J. Schneider,
L. Tal-Or,
B. Tingley,
J. Weingrill,
G. Wuchterl
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery by the CoRoT space mission of a new giant
planet, CoRoT-20b. The planet has a mass of 4.24 ± 0.23
MJup and a radius of 0.84 ± 0.04 RJup. With
a mean density of 8.87 ± 1.10 g cm-3, it is among the
most compact planets known so far. Evolutionary models for the planet
suggest a mass of heavy elements of the order of 800 M⊕
if embedded in a central core, requiring a revision either of the planet
formation models or both planet evolution and structure models. We note
however that smaller amounts of heavy elements are expected by more
realistic models in which they are mixed throughout the envelope. The
planet orbits a G-type star with an orbital period of 9.24 days and an
eccentricity of 0.56.The star's projected rotational velocity is vsini =
4.5 ± 1.0 km s-1, corresponding to a spin period of
11.5 ± 3.1 days if its axis of rotation is perpendicular to the
orbital plane. In the framework of Darwinian theories and neglecting
stellar magnetic breaking, we calculate the tidal evolution of the
system and show that CoRoT-20b is presently one of the very few
Darwin-stable planets that is evolving toward a triple synchronous state
with equality of the orbital, planetary and stellar spin periods.
The CoRoT space mission, launched on December 27th 2006, has been
developed and is operated by CNES, with the contribution of Austria,
Belgium, Brazil, ESA (RSSD and Science Programme), Germany, and Spain.
Astronomy and Astrophysics 01/2012; 538:145. · 4.59 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: [1] The nightside oxygen exosphere of Venus is investigated for high and moderate solar activity by means of a Monte-Carlo model. Hot O atoms are assumed to be produced by dissociative recombination of O2+ and NO+ molecular ions and by charge transfer processes between ionospheric O+ ions and neutral O and H atoms. The model considers rotational and vibrational excitation of the initial energy distribution of hot O atoms, includes elastic, inelastic, and quenching collisions between the suprathermal atoms and the ambient neutral atmosphere species, and uses differential cross sections for the determination of the scattering angle in the collisions. The results indicate that dissociative recombination of O2+ is, like at Venus’ dayside, the most efficient source of hot O atoms at the planet’s nightside. For high solar activity, the nightside exospheric density of hot O atoms is about one order of magnitude lower compared to the dayside, although between 2–10 times higher than in previous studies.
Citation: Gröller, H., H. Lammer, H. I. M. Lichtenegger, M. Pfleger, O. Dutuit, V. I. Shematovich, Y. N. Kulikov, and H. K. Biernat (2012), Hot oxygen atoms in the Venus nightside exosphere, Geophys. Res. Lett., 39, L03202, doi:10.1029/2011GL050421.
Geophysical Research Letters 01/2012; 39(L03202). · 3.79 Impact Factor
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M. Leitzinger,
P. Odert,
Yu.N. Kulikov, H. Lammer,
G. Wuchterl,
T. Penze,
M.G. Guarcello,
G. Micela,
M.L. Khodachenko,
J. Weingrill,
A. Hanslmeier,
H.K. Biernat,
J. Schneider
Planetary and Space Science 01/2012; 62(1):160-161. · 2.22 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: When examining thermal atmospheric escape, usually either Jeans escape or hydrodynamic escape is
considered. Jeans escape, where particles with velocities higher than the escape velocity can escape a
planetary atmosphere, is usually considered, when particles in a collision-free region are examined.
Hydrodynamic escape, on the other hand, presumes that the outflowing gas can be considered as a continuous, homogeneous medium where neither light, nor heavy particles can be discriminated from each other. Recently, Strobel (2009) applied a so-called ‘slow hydrodynamic escape model’, which describes cases intermediate between Jeans escape and hydrodynamic escape, for the nitrogen and methane molecules in Titan’s upper atmosphere. This model requires an extended quasi-collisional region above the exobase where efficient energy transfer can presumably occur. In this study, we examine the collision probability of nitrogen and methane molecules with ambient atmospheric particles within Titan’s exosphere using a modified Monte Carlo code introduced by Wurz and Lammer (2003), to analyze if the ‘slow hydrodynamic escape model’ is applicable to Titan’s exosphere or not. Our results show that the collision probability of nitrogen and methane within Titan’s exosphere decreases quickly with height above the exobase. Also, the probability of a nitrogen or a methane molecule to collide with another heavy molecule is far larger than the probability of a collision with a light particle, since in the region where nitrogen and methane are mainly present, the heavy molecules dominate the light molecules by a factor of 10–100. The results of our particle simulation do not confirm the existence of an extended quasi-collisional region above the exobase, where heavy, slow molecules can gain the escape velocity through collisions with light, fast particles.
Planetary and Space Science 01/2012; 61:79-84. · 2.22 Impact Factor
