71 research outputs found
Deuterium burning in objects forming via the core accretion scenario - Brown dwarfs or planets?
Aims. Our aim is to study deuterium burning in objects forming according to
the core accretion scenario in the hot and cold start assumption and what
minimum deuterium burning mass limit is found for these objects. We also study
how the burning process influences the structure and luminosity of the objects.
Furthermore we want to test and verify our results by comparing them to already
existing hot start simulations which did not consider, however, the formation
process.
Methods. We present a new method to calculate deuterium burning of objects in
a self-consistently coupled model of planet formation and evolution. We discuss
which theory is used to describe the process of deuterium burning and how it
was implemented.
Results. We find that the objects forming according to a hot start scenario
behave approximately in the same way as found in previous works of evolutionary
calculations, which did not consider the formation. However, for cold start
objects one finds that the objects expand during deuterium burning instead of
being partially stabilized against contraction. In both cases, hot and cold
start, the mass of the solid core has an influence on the minimum mass limit of
deuterium burning. The general position of the mass limit, 13 MJ, stays however
approximately the same. None of the investigated parameters was able to change
this mass limit by more than 0.8 MJ. Due to deuterium burning, the luminosity
of hot and cold start objects becomes comparable after ~ 200 Myrs.Comment: Accepted to A&A. Identical as v1 except for corrected typos. 22
pages, 15 figure
Formation, Orbital and Internal Evolutions of Young Planetary Systems
The growing body of observational data on extrasolar planets and
protoplanetary disks has stimulated intense research on planet formation and
evolution in the past few years. The extremely diverse, sometimes unexpected
physical and orbital characteristics of exoplanets lead to frequent updates on
the mainstream scenarios for planet formation and evolution, but also to the
exploration of alternative avenues. The aim of this review is to bring together
classical pictures and new ideas on the formation, orbital and internal
evolutions of planets, highlighting the key role of the protoplanetary disk in
the various parts of the theory. We begin by briefly reviewing the conventional
mechanism of core accretion by the growth of planetesimals, and discuss a
relatively recent model of core growth through the accretion of pebbles. We
review the basic physics of planet-disk interactions, recent progress in this
area, and discuss their role in observed planetary systems. We address the most
important effects of planets internal evolution, like cooling and contraction,
the mass-luminosity relation, and the bulk composition expressed in the
mass-radius and mass-mean density relations.Comment: 49 pages, 12 figures, accepted for publication in Space Science
Reviews. Chapter in International Space Science Institute (ISSI) Book on "The
Disk in Relation to the Formation of Planets and their Proto-atmospheres" to
be published in Space Science Reviews by Springe
Atmospheric retrievals with petitRADTRANS
petitRADTRANS (pRT) is a fast radiative transfer code used for computing
emission and transmission spectra of exoplanet atmospheres, combining a FORTRAN
back end with a Python based user interface. It is widely used in the exoplanet
community with 161 references in the literature to date, and has been
benchmarked against numerous similar tools. The spectra calculated with pRT can
be used as a forward model for fitting spectroscopic data using Monte Carlo
techniques, commonly referred to as an atmospheric retrieval. The new retrieval
module combines fast forward modelling with nested sampling codes, allowing for
atmospheric retrievals on a large range of different types of exoplanet data.
Thus it is now possible to use pRT to easily and quickly infer the atmospheric
properties of exoplanets in both transmission and thermal emission.Comment: 5 pages, 1 figure, submitted to the Journal of Open Source Softwar
Model atmospheres of irradiated exoplanets: The influence of stellar parameters, metallicity, and the C/O ratio
Many parameters constraining the spectral appearance of exoplanets are still
poorly understood. We therefore study the properties of irradiated exoplanet
atmospheres over a wide parameter range including metallicity, C/O ratio and
host spectral type. We calculate a grid of 1-d radiative-convective atmospheres
and emission spectra. We perform the calculations with our new
Pressure-Temperature Iterator and Spectral Emission Calculator for Planetary
Atmospheres (PETIT) code, assuming chemical equilibrium. The atmospheric
structures and spectra are made available online. We find that atmospheres of
planets with C/O ratios 1 and 1500 K can exhibit
inversions due to heating by the alkalis because the main coolants CH,
HO and HCN are depleted. Therefore, temperature inversions possibly occur
without the presence of additional absorbers like TiO and VO. At low
temperatures we find that the pressure level of the photosphere strongly
influences whether the atmospheric opacity is dominated by either water (for
low C/O) or methane (for high C/O), or both (regardless of the C/O). For hot,
carbon-rich objects this pressure level governs whether the atmosphere is
dominated by methane or HCN. Further we find that host stars of late spectral
type lead to planetary atmospheres which have shallower, more isothermal
temperature profiles. In agreement with prior work we find that for planets
with 1750 K the transition between water or methane dominated
spectra occurs at C/O 0.7, instead of 1, because condensation
preferentially removes oxygen.Comment: 30 pages, 20 figures. Accepted for publication in Ap
Observing transiting planets with JWST -- Prime targets and their synthetic spectral observations
The James Webb Space Telescope will enable astronomers to obtain exoplanet
spectra of unprecedented precision. Especially the MIRI instrument may shed
light on the nature of the cloud particles obscuring planetary transmission
spectra in the optical and near-infrared. We provide self-consistent
atmospheric models and synthetic JWST observations for prime exoplanet targets
in order to identify spectral regions of interest and estimate the number of
transits needed to distinguish between model setups. We select targets which
span a wide range in planetary temperature and surface gravity, ranging from
super-Earths to giant planets, and have a high expected SNR. For all targets we
vary the enrichment, C/O ratio, presence of optical absorbers (TiO/VO) and
cloud treatment. We calculate atmospheric structures and emission and
transmission spectra for all targets and use a radiometric model to obtain
simulated observations. We analyze JWST's ability to distinguish between
various scenarios. We find that in very cloudy planets such as GJ 1214b less
than 10 transits with NIRSpec may be enough to reveal molecular features.
Further, the presence of small silicate grains in atmospheres of hot Jupiters
may be detectable with a single JWST MIRI transit. For a more detailed
characterization of such particles less than 10 transits are necessary.
Finally, we find that some of the hottest hot Jupiters are well fitted by
models which neglect the redistribution of the insolation and harbor
inversions, and that 1-4 eclipse measurements with NIRSpec are needed to
distinguish between the inversion models. Wet thus demonstrate the capabilities
of JWST for solving some of the most intriguing puzzles in current exoplanet
atmospheric research. Further, by publishing all models calculated for this
study we enable the community to carry out similar or retrieval analyses for
all planets included in our target list.Comment: 24 pages, 7 figures, accepted for publication in A&
Modeling of Exoplanet Atmospheres
Spectrally characterizing exoplanet atmospheres will be one of the fastest moving astronomical disciplines in the years to come. Especially the upcoming James Webb Space Telescope
(JWST) will provide spectral measurements from the near- to mid-infrared of unprecedented precision. With other next generation instruments on the horizon, it is crucial to possess the tools necessary for interpretating observations. To this end I wrote the petitCODE, which solves for the self-consistent atmospheric structures of exoplanets, assuming chemical and radiative-convective equilibrium. The code includes scattering, and models clouds. The code outputs the planet’s observable emission and transmission spectra. In addition, I constructed a spectral retrieval code, which derives the full posterior probability distribution of atmospheric parameters from observations. I used petitCODE to systematically study the atmospheres of hot jupiters and found, e.g., that their structures depend strongly on the type of their host stars. Moreover, I found that C/O ratios around unity can lead to atmospheric inversions. Next, I produced synthetic observations of prime exoplanet targets for JWST, and studied how well we will be able to distinguish various atmospheric scenarios. Finally, I verified the implementation of my retrieval code using mock JWST observations
Evolutionary models of cold and low-mass planets: Cooling curves, magnitudes, and detectability
Future instruments like NIRCam and MIRI on JWST or METIS at the ELT will be
able to image exoplanets that are too faint for current direct imaging
instruments. Evolutionary models predicting the planetary intrinsic luminosity
as a function of time have traditionally concentrated on gas-dominated giant
planets. We extend these cooling curves to Saturnian and Neptunian planets. We
simulate the cooling of isolated core-dominated and gas giant planets with
masses of 5 Earthmasses to 2 Jupitermasses. The luminosity includes the
contribution from the cooling and contraction of the core and of the H/He
envelope, as well as radiogenic decay. For the atmosphere we use grey,
AMES-Cond, petitCODE, and HELIOS models. We consider solar and non-solar
metallicities as well as cloud-free and cloudy atmospheres. The most important
initial conditions, namely the core-to-envelope ratio and the initial
luminosity are taken from planet formation simulations based on the core
accretion paradigm. We first compare our cooling curves for Uranus, Neptune,
Jupiter, Saturn, GJ 436b, and a 5 Earthmass-planet with a 1% H/He envelope with
other evolutionary models. We then present the temporal evolution of planets
with masses between 5 Earthmasses and 2 Jupitermasses in terms of their
luminosity, effective temperature, radius, and entropy. We discuss the impact
of different post formation entropies. For the different atmosphere types and
initial conditions magnitudes in various filter bands between 0.9 and 30
micrometer wavelength are provided. Using black body fluxes and non-grey
spectra, we estimate the detectability of such planets with JWST. It is found
that a 20 (100) Earthmass-planet can be detected with JWST in the background
limit up to an age of about 10 (100) Myr with NIRCam and MIRI, respectively.Comment: Language corrected version and improved arrangements of figures,
online data at:
http://www.space.unibe.ch/research/research_groups/planets_in_time/numerical_data/index_eng.htm
Magma ocean evolution of the TRAPPIST-1 planets
Funding: P.B. acknowledges a St Leonard’s Interdisciplinary Doctoral Scholarship from the University of St Andrews. L.C. acknowledges support from the DFG Priority Programme SP1833 Grant CA 1795/3. R.B.’s contribution was supported by NASA grant number 80NSSC20K0229 and the NASA Virtual Planetary Laboratory Team through grant number 80NSSC18K0829. Th.H. acknowledges support from the European Research Council under the Horizon 2020 Framework Program via the ERC Advanced Grant Origins 83 24 28.Recent observations of the potentially habitable planets TRAPPIST-1 e, f, and g suggest that they possess large water mass fractions of possibly several tens of weight percent of water, even though the host star's activity should drive rapid atmospheric escape. These processes can photolyze water, generating free oxygen and possibly desiccating the planet. After the planets formed, their mantles were likely completely molten with volatiles dissolving and exsolving from the melt. To understand these planets and prepare for future observations, the magma ocean phase of these worlds must be understood. To simulate these planets, we have combined existing models of stellar evolution, atmospheric escape, tidal heating, radiogenic heating, magma-ocean cooling, planetary radiation, and water-oxygen-iron geochemistry. We present MagmOc, a versatile magma-ocean evolution model, validated against the rocky super-Earth GJ 1132b and early Earth. We simulate the coupled magma-ocean atmospheric evolution of TRAPPIST-1 e, f, and g for a range of tidal and radiogenic heating rates, as well as initial water contents between 1 and 100 Earth oceans. We also reanalyze the structures of these planets and find they have water mass fractions of 0–0.23, 0.01–0.21, and 0.11–0.24 for planets e, f, and g, respectively. Our model does not make a strong prediction about the water and oxygen content of the atmosphere of TRAPPIST-1 e at the time of mantle solidification. In contrast, the model predicts that TRAPPIST-1 f and g would have a thick steam atmosphere with a small amount of oxygen at that stage. For all planets that we investigated, we find that only 3–5% of the initial water will be locked in the mantle after the magma ocean solidified.Publisher PDFPeer reviewe
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