860 research outputs found
A New Family of Planets ? "Ocean Planets"
A new family of planets is considered which is between rochy terrestrial
planets and gaseous giant ones: "Ocean-Planets". We present the possible
formation, composition and internal models of these putative planets, including
that of their ocean, as well as their possible Exobiology interest. These
planets should be detectable by planet detection missions such as Eddington and
Kepler, and possibly COROT (lauch scheduled in 2006). They would be ideal
targets for spectroscopic missions such as Darwin/TPF.Comment: 15 pages, 3 figures submitted to Icarus notes (10 july 2003
Young planets under extreme UV irradiation. I. Upper atmosphere modelling of the young exoplanet K2-33b
The K2-33 planetary system hosts one transiting ~5 R_E planet orbiting the
young M-type host star. The planet's mass is still unknown, with an estimated
upper limit of 5.4 M_J. The extreme youth of the system (<20 Myr) gives the
unprecedented opportunity to study the earliest phases of planetary evolution,
at a stage when the planet is exposed to an extremely high level of high-energy
radiation emitted by the host star. We perform a series of 1D hydrodynamic
simulations of the planet's upper atmosphere considering a range of possible
planetary masses, from 2 to 40 M_E, and equilibrium temperatures, from 850 to
1300 K, to account for internal heating as a result of contraction. We obtain
temperature profiles mostly controlled by the planet's mass, while the
equilibrium temperature has a secondary effect. For planetary masses below 7-10
M_E, the atmosphere is subject to extremely high escape rates, driven by the
planet's weak gravity and high thermal energy, which increase with decreasing
mass and/or increasing temperature. For higher masses, the escape is instead
driven by the absorption of the high-energy stellar radiation. A rough
comparison of the timescales for complete atmospheric escape and age of the
system indicates that the planet is more massive than 10 M_E.Comment: 11 pages, 7 figure
A grid of upper atmosphere models for 1--40 MEARTH planets: application to CoRoT-7 b and HD219134 b,c
There is growing observational and theoretical evidence suggesting that
atmospheric escape is a key driver of planetary evolution. Commonly, planetary
evolution models employ simple analytic formulae (e.g., energy limited escape)
that are often inaccurate, and more detailed physical models of atmospheric
loss usually only give snapshots of an atmosphere's structure and are difficult
to use for evolutionary studies. To overcome this problem, we upgrade and
employ an already existing upper atmosphere hydrodynamic code to produce a
large grid of about 7000 models covering planets with masses 1 - 39 Earth mass
with hydrogen-dominated atmospheres and orbiting late-type stars. The modeled
planets have equilibrium temperatures ranging between 300 and 2000 K. For each
considered stellar mass, we account for three different values of the
high-energy stellar flux (i.e., low, moderate, and high activity). For each
computed model, we derive the atmospheric temperature, number density, bulk
velocity, X-ray and EUV (XUV) volume heating rates, and abundance of the
considered species as a function of distance from the planetary center. From
these quantities, we estimate the positions of the maximum dissociation and
ionisation, the mass-loss rate, and the effective radius of the XUV absorption.
We show that our results are in good agreement with previously published
studies employing similar codes. We further present an interpolation routine
capable to extract the modelling output parameters for any planet lying within
the grid boundaries. We use the grid to identify the connection between the
system parameters and the resulting atmospheric properties. We finally apply
the grid and the interpolation routine to estimate atmospheric evolutionary
tracks for the close-in, high-density planets CoRoT-7 b and HD219134 b,c...Comment: 21 pages, 4 Tables, 15 Figure
Stellar wind interaction and pick-up ion escape of the Kepler-11 "super-Earths"
We study the interactions between stellar wind and the extended
hydrogen-dominated upper atmospheres of planets and the resulting escape of
planetary pick-up ions from the 5 "super-Earths" in the compact Kepler-11
system and compare the escape rates with the efficiency of the thermal escape
of neutral hydrogen atoms. Assuming the stellar wind of Kepler-11 is similar to
the solar wind, we use a polytropic 1D hydrodynamic wind model to estimate the
wind properties at the planetary orbits. We apply a Direct Simulation Monte
Carlo Model to model the hydrogen coronae and the stellar wind plasma
interaction around Kepler-11b-f within a realistic expected heating efficiency
range of 15-40%. The same model is used to estimate the ion pick-up escape from
the XUV heated and hydrodynamically extended upper atmospheres of Kepler-11b-f.
From the interaction model we study the influence of possible magnetic moments,
calculate the charge exchange and photoionization production rates of planetary
ions and estimate the loss rates of pick-up H+ ions for all five planets. We
compare the results between the five "super-Earths" and in a more general sense
also with the thermal escape rates of the neutral planetary hydrogen atoms. Our
results show that for all Kepler-11b-f exoplanets, a huge neutral hydrogen
corona is formed around the planet. The non-symmetric form of the corona
changes from planet to planet and is defined mostly by radiation pressure and
gravitational effects. Non-thermal escape rates of pick-up ionized hydrogen
atoms for Kepler-11 "super-Earths" vary between approximately 6.4e30 1/s and
4.1e31 1/s depending on the planet's orbital location and assumed heating
efficiency. These values correspond to non-thermal mass loss rates of
approximately 1.07e7 g/s and 6.8e7 g/s respectively, which is a few percent of
the thermal escape rates.Comment: 8 pages, 3 figures, accepted to A&
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