14 research outputs found
Impacts of planet migration models on planetary populations. Effects of saturation, cooling and stellar irradiation
Context: Several recent studies have found that planet migration in adiabatic
discs differs significantly from migration in isothermal discs. Depending on
the thermodynamic conditions, i.e., the effectiveness of radiative cooling, and
the radial surface density profile, planets migrate inward or outward. Clearly,
this will influence the semimajor axis - mass distribution of planets as
predicted by population synthesis simulations. Aims: Our goal is to study the
global effects of radiative cooling, viscous torque desaturation and gap
opening as well as stellar irradiation on the tidal migration of a synthetic
planet population. Methods: We combine results from several analytical studies
and 3D hydrodynamic simulations in a new semi-analytical migration model for
the application in our planet population synthesis calculations. Results: We
find a good agreement of our model with torques obtained in a 3D radiative
hydrodynamic simulations. We find three convergence zones in a typical disc,
towards which planets migrate from the in- and outside, affecting strongly the
migration behavior of low-mass planets. Interestingly, this leads to slow type
II like migration behavior for low-mass planets captured in those zones even
without an ad hoc migration rate reduction factor or a yet to be defined
halting mechanism. This means that the new prescription of migration including
non-isothermal effects makes the preciously widely used artificial migration
rate reduction factor obsolete. Conclusions: Outward migration in parts of a
disc makes some planets survive long enough to become massive. The convergence
zones lead to a potentially observable accumulations of low-mass planets at
certain semimajor axes. Our results indicate that further studies of the mass
where the corotation torque saturates will be needed since its value has a
major impact on the properties of planet populations.Comment: 18 pages, 15 figures. Accepted for A&
Application of recent results on the orbital migration of low mass planets: convergence zones
Previous models of the combined growth and migration of protoplanets needed
large ad hoc reduction factors for the type I migration rate as found in the
isothermal approximation. In order to eliminate these factors, a simple
semi-analytical model is presented that incorporates recent results on the
migration of low mass planets in non-isothermal disks. It allows for outward
migration. The model is used to conduct planetary populations synthesis
calculations. Two points with zero torque are found in the disks. Planets
migrate both in- and outward towards these convergence zones. They could be
important for accelerating planetary growth by concentrating matter in one
point. We also find that the updated type I migration models allow the
formation of both close-in low mass planets, but also of giant planets at large
semimajor axes. The problem of too rapid migration is significantly mitigated.Comment: 4 pages, 3 figures. Proceedings of the IAU Symposium 276, 2010: The
Astrophysics of Planetary Systems: Formation, Structure, and Dynamical
Evolution, ed. A. Sozzetti, M. G. Lattanzi, and A. P. Bos
Planet Populations as a Function of Stellar Properties
Exoplanets around different types of stars provide a window into the diverse
environments in which planets form. This chapter describes the observed
relations between exoplanet populations and stellar properties and how they
connect to planet formation in protoplanetary disks. Giant planets occur more
frequently around more metal-rich and more massive stars. These findings
support the core accretion theory of planet formation, in which the cores of
giant planets form more rapidly in more metal-rich and more massive
protoplanetary disks. Smaller planets, those with sizes roughly between Earth
and Neptune, exhibit different scaling relations with stellar properties. These
planets are found around stars with a wide range of metallicities and occur
more frequently around lower mass stars. This indicates that planet formation
takes place in a wide range of environments, yet it is not clear why planets
form more efficiently around low mass stars. Going forward, exoplanet surveys
targeting M dwarfs will characterize the exoplanet population around the lowest
mass stars. In combination with ongoing stellar characterization, this will
help us understand the formation of planets in a large range of environments.Comment: Accepted for Publication in the Handbook of Exoplanet
Planetary population synthesis
In stellar astrophysics, the technique of population synthesis has been
successfully used for several decades. For planets, it is in contrast still a
young method which only became important in recent years because of the rapid
increase of the number of known extrasolar planets, and the associated growth
of statistical observational constraints. With planetary population synthesis,
the theory of planet formation and evolution can be put to the test against
these constraints. In this review of planetary population synthesis, we first
briefly list key observational constraints. Then, the work flow in the method
and its two main components are presented, namely global end-to-end models that
predict planetary system properties directly from protoplanetary disk
properties and probability distributions for these initial conditions. An
overview of various population synthesis models in the literature is given. The
sub-models for the physical processes considered in global models are
described: the evolution of the protoplanetary disk, the planets' accretion of
solids and gas, orbital migration, and N-body interactions among concurrently
growing protoplanets. Next, typical population synthesis results are
illustrated in the form of new syntheses obtained with the latest generation of
the Bern model. Planetary formation tracks, the distribution of planets in the
mass-distance and radius-distance plane, the planetary mass function, and the
distributions of planetary radii, semimajor axes, and luminosities are shown,
linked to underlying physical processes, and compared with their observational
counterparts. We finish by highlighting the most important predictions made by
population synthesis models and discuss the lessons learned from these
predictions - both those later observationally confirmed and those rejected.Comment: 47 pages, 12 figures. Invited review accepted for publication in the
'Handbook of Exoplanets', planet formation section, section editor: Ralph
Pudritz, Springer reference works, Juan Antonio Belmonte and Hans Deeg, Ed
Connecting Planetary Composition with Formation
The rapid advances in observations of the different populations of
exoplanets, the characterization of their host stars and the links to the
properties of their planetary systems, the detailed studies of protoplanetary
disks, and the experimental study of the interiors and composition of the
massive planets in our solar system provide a firm basis for the next big
question in planet formation theory. How do the elemental and chemical
compositions of planets connect with their formation? The answer to this
requires that the various pieces of planet formation theory be linked together
in an end-to-end picture that is capable of addressing these large data sets.
In this review, we discuss the critical elements of such a picture and how they
affect the chemical and elemental make up of forming planets. Important issues
here include the initial state of forming and evolving disks, chemical and dust
processes within them, the migration of planets and the importance of planet
traps, the nature of angular momentum transport processes involving turbulence
and/or MHD disk winds, planet formation theory, and advanced treatments of disk
astrochemistry. All of these issues affect, and are affected by the chemistry
of disks which is driven by X-ray ionization of the host stars. We discuss how
these processes lead to a coherent end-to-end model and how this may address
the basic question.Comment: Invited review, accepted for publication in the 'Handbook of
Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018). 46 pages, 10
figure
Characterization of exoplanets from their formation
Context. The research of extrasolar planets has entered an era in which
we characterize extrasolar planets. This has become possible with measurements of the
radii of transiting planets and of the luminosity of planets observed by direct imaging.
Meanwhile, the precision of radial velocity surveys makes it possible to discover not only
giant planets but also very low-mass ones.
Aims. Uniting all these different observational constraints into one
coherent picture to better understand planet formation is an important and simultaneously
difficult undertaking. One approach is to develop a theoretical model that can make
testable predictions for all these observational techniques. Our goal is to have such a
model and use it in population synthesis calculations.
Methods. In a companion paper, we described how we have extended our
formation model into a self-consistently coupled formation and evolution
model. In this second paper, we first continue with the model description. We describe how
we calculate the internal structure of the solid core of the planet and include radiogenic
heating. We also introduce an upgrade of the protoplanetary disk model. Finally, we use
the upgraded model in population synthesis calculations.
Results. We present how the planetary mass-radius relationship of
planets with primordial H2/He envelopes forms and evolves in time. The basic
shape of the mass-radius relationship can be understood from the core accretion model.
Low-mass planets cannot bind massive envelopes, while super-critical cores necessarily
trigger runway gas accretion, leading to “forbidden” zones in the
M − R plane. For a given mass, there is a considerable
diversity of radii, mainly due to different bulk compositions, reflecting different
formation histories. We compare the synthetic
M − R plane with the observed one, finding good
agreement for a > 0.1 AU. The synthetic planetary
radius distribution is characterized by a strong increase towards small R
and a second, lower local maximum at about 1 RX. The
increase towards small radii comes from the increase of the mass function towards
low M. The second local maximum is due to the fact that radii are
nearly independent of mass for giant planets. A comparison of the synthetic radius
distribution with Kepler data shows good agreement for
R ≳ 2 R⊕, but divergence for smaller
radii. This indicates that for R ≳ 2 R⊕
the radius distribution can be described with planets with primordial
H2/He atmospheres, while at smaller radii, planets of a different nature
dominate. We predict that in the next few years, Kepler will find the
second local maximum at about 1 RX.
Conclusions. With the updated model, we can compute the most important
quantities, like mass, semimajor axis, radius, and luminosity, which characterize an
extrasolar planet self-consistently from its formation. The comparison of the radii of the
synthetic planets with observations makes it possible to better constrain this formation
process and to distinguish between fundamental types of planets
Progress of a Si H muc Si H Tandem Solar Module Production on Substrate Size of 2,60 x 2,20 m2 at Sunfilm
Characterization of exoplanets from their formation
The research of exoplanets has entered an era in which we characterize
extrasolar planets. This has become possible with measurements of radii and
luminosities. Meanwhile, radial velocity surveys discover also very low-mass
planets. Uniting all this observational data into one coherent picture to
better understand planet formation is an important, but difficult undertaking.
Our approach is to develop a model which can make testable predictions for all
these observational methods. We continue to describe how we have extended our
formation model into a self-consistently coupled formation and evolution model.
We show how we calculate the internal structure of the solid core and
radiogenic heating. We also improve the protoplanetary disk model. Finally, we
conduct population synthesis calculations. We present how the planetary
mass-radius relationship of planets with primordial H/He envelopes forms and
evolves in time. The basic shape of the M-R relation can be understood from the
core accretion model. Low-mass planets cannot bind massive envelopes, while
super-critical cores necessarily trigger runway gas accretion, leading to
"forbidden" zones in the M-R plane. For a given mass, there is a considerable
diversity of radii. We compare the synthetic M-R relation with the observed
one, finding good agreement for a>0.1 AU. The synthetic radius distribution is
characterized by a strong increase towards small R, and a second, lower local
maximum at ~1 Jovian radius. The increase towards small radii reflects the
increase of the mass function towards low M. The second local maximum is due to
the fact that radii are nearly independent of mass for giant planets. A
comparison of the synthetic radius distribution with Kepler data shows
agreement for R>2 Earth radii, but divergence for smaller radii. We predict
that in the next few years, Kepler should find the second, local maximum at ~1
Jovian radius.Comment: Accepted to A&A. Minor revisions only relative to v