800 research outputs found
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 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
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
An Impacting Descent Probe for Europa and the other Galilean Moons of Jupiter
We present a study of an impacting descent probe that increases the science
return of spacecraft orbiting or passing an atmosphere-less planetary body of
the solar system, such as the Galilean moons of Jupiter. The descent probe is a
carry-on small spacecraft (< 100 kg), to be deployed by the mother spacecraft,
that brings itself onto a collisional trajectory with the targeted planetary
body in a simple manner. A possible science payload includes instruments for
surface imaging, characterisation of the neutral exosphere, and magnetic field
and plasma measurement near the target body down to very low-altitudes (~1 km),
during the probe's fast (~km/s) descent to the surface until impact. The
science goals and the concept of operation are discussed with particular
reference to Europa, including options for flying through water plumes and
after-impact retrieval of very-low altitude science data. All in all, it is
demonstrated how the descent probe has the potential to provide a high science
return to a mission at a low extra level of complexity, engineering effort, and
risk. This study builds upon earlier studies for a Callisto Descent Probe (CDP)
for the former Europa-Jupiter System Mission (EJSM) of ESA and NASA, and
extends them with a detailed assessment of a descent probe designed to be an
additional science payload for the NASA Europa Mission.Comment: 34 pages, 11 figure
Roche lobe effects on the atmospheric loss of "Hot Jupiters"
Observational evidence of a hydrodynamically evaporating upper atmosphere of
HD209458b (Vidal-Madjar et al. 2003; 2004) and recent theoretical studies on
evaporation scenarios of ``Hot Jupiters'' in orbits around solar-like stars
with the age of the Sun indicate that the upper atmospheres of short-periodic
exoplanets experience hydrodynamic blow-off conditions resulting in loss rates
of the order of about 10^10 - 10^12 g s^-1 (Lammer et al. 2003; Yelle 2004;
Baraffe et al. 2004; Lecavlier des Etangs et al. 2004; Jaritz et al. 2005, Tian
et al. 2005; Penz et al. 2007). By studying the effect of the Roche lobe on the
atmospheric loss from short-periodic gas giants we found, that the effect of
the Roche lobe can enhance the hydrodynamic evaporation from HD209458b by about
2 and from OGLE-TR-56b by about 2.5 times. For similar exoplanets which are
closer to their host star than OGLE-TR-56b, the enhancement of the mass loss
can be even larger. Moreover, we show that the effect of the Roche lobe raises
the possibility that ``Hot Jupiters'' can reach blow-off conditions at
temperatures which are less than expected (< 10000 K) due to the stellar X-ray
and EUV (XUV) heating.Comment: 4 pages, 2 figures, submitted to A&
Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetized hot Jupiters
We investigate the interaction between the magnetized stellar wind plasma and
the partially ionized hydrodynamic hydrogen outflow from the escaping upper
atmosphere of non- or weakly magnetized hot Jupiters. We use the well-studied
hot Jupiter HD 209458b as an example for similar exoplanets, assuming a
negligible intrinsic magnetic moment. For this planet, the stellar wind plasma
interaction forms an obstacle in the planet's upper atmosphere, in which the
position of the magnetopause is determined by the condition of pressure balance
between the stellar wind and the expanded atmosphere, heated by the stellar
extreme ultraviolet (EUV) radiation. We show that the neutral atmospheric atoms
penetrate into the region dominated by the stellar wind, where they are ionized
by photo-ionization and charge exchange, and then mixed with the stellar wind
flow. Using a 3D magnetohydrodynamic (MHD) model, we show that an induced
magnetic field forms in front of the planetary obstacle, which appears to be
much stronger compared to those produced by the solar wind interaction with
Venus and Mars. Depending on the stellar wind parameters, because of the
induced magnetic field, the planetary obstacle can move up to ~0.5-1 planetary
radii closer to the planet. Finally, we discuss how estimations of the
intrinsic magnetic moment of hot Jupiters can be inferred by coupling
hydrodynamic upper planetary atmosphere and MHD stellar wind interaction models
together with UV observations. In particular, we find that HD 209458b should
likely have an intrinsic magnetic moment of 10-20% that of Jupiter.Comment: 8 pages, 6 figures, 2 tables, accepted to MNRA
Could we identify hot Ocean-Planets with CoRoT, Kepler and Doppler velocimetry?
Planets less massive than about 10 MEarth are expected to have no massive
H-He atmosphere and a cometary composition (50% rocks, 50% water, by mass)
provided they formed beyond the snowline of protoplanetary disks. Due to inward
migration, such planets could be found at any distance between their formation
site and the star. If migration stops within the habitable zone, this will
produce a new kind of planets, called Ocean-Planets. Ocean-planets typically
consist in a silicate core, surrounded by a thick ice mantle, itself covered by
a 100 km deep ocean. The existence of ocean-planets raises important
astrobiological questions: Can life originate on such body, in the absence of
continent and ocean-silicate interfaces? What would be the nature of the
atmosphere and the geochemical cycles ?
In this work, we address the fate of Hot Ocean-Planets produced when
migration ends at a closer distance. In this case the liquid/gas interface can
disappear, and the hot H2O envelope is made of a supercritical fluid. Although
we do not expect these bodies to harbor life, their detection and
identification as water-rich planets would give us insight as to the abundance
of hot and, by extrapolation, cool Ocean-Planets.Comment: 47 pages, 6 Fugures, regular paper. Submitted to Icaru
Multi-object spectroscopy of stars in the CoRoT fields I: Early-type stars in the CoRoT-fields IRa01, LRa01, LRa02
Observations of giant stars indicate that the frequency of giant planets is
much higher for intermediate-mass stars than for solar-like stars. Up to now
all known planets of giant stars orbit at relatively far distances from their
host stars. It is not known whether intermediate-mass stars also had many
close-in planets when they were on the main sequence, which were then engulfed
when the star became a giant star. To understand the formation and evolution of
planets it is therefore important to find out whether main-sequence stars of
intermediate-mass have close-in planets or not. A survey for transiting planets
of intermediate-mass stars would be ideal to solve this question, because the
detection of transiting planets is not affected by the rapid rotation of these
stars. As a first step for an efficient survey we need to identify
intermediate-mass stars in the CoRoT-fields, which can then be used as an input
list. To compile the input list we derived the spectral types of essentially
all O, B and A stars down to 14.5 mag in the CoRoT fields IRa01, LRa01, LRa02
taken with the multi-object spectrograph AAOmega. We determined the spectral
types by comparing the spectra with template spectra from a library. In total
we identify 1856 A and B stars that have been observed with CoRoT. Given the
number of planets that have been detected in these fields amongst late-type
stars, we estimate that there are one to four transiting planets of
intermediate-mass stars waiting to be discovered. Our survey not only allows us
to carry out a dedicated planet search programme but is also essential for any
types of studies of the light curves of early-type stars in the CoRoT database.
We also show that it would be possible to extend the survey to all fields that
CoRoT has observed using photometrically determined spectral types.Comment: 57 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
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