21 research outputs found
Planetary population synthesis and the emergence of four classes of planetary system architectures
Planetary population synthesis and the emergence of four classes of planetary system architectures
The formation of Jupiter by hybrid pebble-planetesimal accretion
The standard model for giant planet formation is based on the accretion of
solids by a growing planetary embryo, followed by rapid gas accretion once the
planet exceeds a so-called critical mass. The dominant size of the accreted
solids (cm-size particles named pebbles or km to hundred km-size bodies named
planetesimals) is, however, unknown. Recently, high-precision measurements of
isotopes in meteorites provided evidence for the existence of two reservoirs in
the early Solar System. These reservoirs remained separated from ~1 until ~ 3
Myr after the beginning of the Solar System's formation. This separation is
interpreted as resulting from Jupiter growing and becoming a barrier for
material transport. In this framework, Jupiter reached ~20 Earth masses within
~1 Myr and slowly grew to ~50 Earth masses in the subsequent 2 Myr before
reaching its present-day mass. The evidence that Jupiter slowed down its growth
after reaching 20 Earth masses for at least 2 Myr is puzzling because a planet
of this mass is expected to trigger fast runaway gas accretion. Here, we use
theoretical models to describe the conditions allowing for such a slow
accretion and show that Jupiter grew in three distinct phases. First, rapid
pebble accretion brought the major part of Jupiter's core mass. Second, slow
planetesimal accretion provided the energy required to hinder runaway gas
accretion during 2 Myr. Third, runaway gas accretion proceeded. Both pebbles
and planetesimals therefore have an important role in Jupiter's formation.Comment: Published in Nature Astronomy on August 27, 201
Towards a population synthesis of discs and planets. II. Confronting disc models and observations at the population level
Aims. We want to find the distribution of initial conditions that best
reproduces disc observations at the population level. Methods. We first ran a
parameter study using a 1D model that includes the viscous evolution of a gas
disc, dust, and pebbles, coupled with an emission model to compute the
millimetre flux observable with ALMA. This was used to train a machine learning
surrogate model that can compute the relevant quantity for comparison with
observations in seconds. This surrogate model was used to perform parameter
studies and synthetic disc populations. Results. Performing a parameter study,
we find that internal photoevaporation leads to a lower dependency of disc
lifetime on stellar mass than external photoevaporation. This dependence should
be investigated in the future. Performing population synthesis, we find that
under the combined losses of internal and external photoevaporation, discs are
too short lived. Conclusions. To match observational constraints, future models
of disc evolution need to include one or a combination of the following
processes: infall of material to replenish the discs, shielding of the disc
from internal photoevaporation due to magnetically driven disc winds, and
extinction of external high-energy radiation. Nevertheless, disc properties in
low-external-photoevaporation regions can be reproduced by having more massive
and compact discs. Here, the optimum values of the viscosity parameter
lie between and and with internal photoevaporation
being the main mode of disc dispersal.Comment: Accepted for publication in A&A; minor changes in the reference lis
A water budget dichotomy of rocky protoplanets from Al-heating
In contrast to the water-poor inner solar system planets, stochasticity
during planetary formation and order of magnitude deviations in exoplanet
volatile contents suggest that rocky worlds engulfed in thick volatile ice
layers are the dominant family of terrestrial analogues among the extrasolar
planet population. However, the distribution of compositionally Earth-like
planets remains insufficiently constrained, and it is not clear whether the
solar system is a statistical outlier or can be explained by more general
planetary formation processes. Here we employ numerical models of planet
formation, evolution, and interior structure, to show that a planet's bulk
water fraction and radius are anti-correlated with initial Al levels in
the planetesimal-based accretion framework. The heat generated by this
short-lived radionuclide rapidly dehydrates planetesimals prior to accretion
onto larger protoplanets and yields a system-wide correlation of planet bulk
abundances, which, for instance, can explain the lack of a clear orbital trend
in the water budgets of the TRAPPIST-1 planets. Qualitatively, our models
suggest two main scenarios of planetary systems' formation: high-Al
systems, like our solar system, form small, water-depleted planets, whereas
those devoid of Al predominantly form ocean worlds, where the mean
planet radii between both scenarios deviate by up to about 10%.Comment: Preprint version; free-to-read journal version at
https://rdcu.be/bmdlw; blog article at https://t.co/p6SValG1i
Planetary system architectures with low-mass inner planets: Direct imaging exploration of mature systems beyond 1 au
The discovery of planets orbiting at less than 1 au from their host star and
less massive than Saturn in various exoplanetary systems revolutionized our
theories of planetary formation. The fundamental question is whether these
close-in low-mass planets could have formed in the inner disk interior to 1 au,
or whether they formed further out in the planet-forming disk and migrated
inward. Exploring the role of additional giant planets in these systems may
help us to pinpoint their global formation and evolution. We searched for
additional substellar companions by using direct imaging in systems known to
host close-in small planets. The use of direct imaging complemented by radial
velocity and astrometric detection limits enabled us to explore the giant
planet and brown dwarf demographics around these hosts to investigate the
potential connection between both populations. We carried out a direct imaging
survey with VLT/SPHERE to look for outer giant planets and brown dwarf
companions in 27 systems hosting close-in low-mass planets discovered by radial
velocity. Our sample is composed of very nearby (<20pc) planetary systems,
orbiting G-, K-, and M-type mature (0.5-10Gyr) stellar hosts. We performed
homogeneous direct imaging data reduction and analysis to search for and
characterize point sources, and derived robust statistical detection limits. Of
337 point-source detections, we do not find any new bound companions. We
recovered the emblematic very cool T-type brown dwarf GJ229B. Our typical
sensitivities in direct imaging range from 5 to 30 MJup beyond 2 au. The
non-detection of massive companions is consistent with predictions based on
models of planet formation by core accretion. Our pilot study opens the way to
a multi-technique approach for the exploration of very nearby exoplanetary
systems with future ground-based and space observatories.Comment: 49 pages including 31 pages of appendices and references, 31 figures,
A&A, accepte
EDEN Survey: Small Transiting Planet Detection Limits and Constraints on the Occurrence Rates for Late M Dwarfs within 15 pc
Earth-sized exoplanets that transit nearby, late spectral type red dwarfs
will be prime targets for atmospheric characterization in the coming decade.
Such systems, however, are difficult to find via wide-field transit surveys
like Kepler or TESS. Consequently, the presence of such transiting planets is
unexplored and the occurrence rates of short-period Earth-sized planets around
late M dwarfs remain poorly constrained. Here, we present the deepest
photometric monitoring campaign of 22 nearby late M dwarf stars, using data
from over 500 nights on seven 1-2 meter class telescopes. Our survey includes
all known single quiescent northern late M dwarfs within 15 pc. We use
transit-injection-and-recovery tests to quantify the completeness of our
survey, successfully identify most () transiting short-period (0.5-1 d)
super-Earths (), and are sensitive () to transiting
Earth-sized planets (). Our high sensitivity to transits with
a near-zero false positive rate demonstrates an efficient survey strategy. Our
survey does not yield a transiting planet detection, yet it provides the most
sensitive upper limits on transiting planets orbiting our target stars.
Finally, we explore multiple hypotheses about the occurrence rates of
short-period planets (from Earth-sized planets to giant planets) around late M
dwarfs. We show, for example, that giant planets at short periods ( day)
are uncommon around our target stars. Our dataset provides some insight into
occurrence rates of short-period planets around TRAPPIST-1-like stars, and our
results can help test planetary formation and system evolution models, as well
as guide future observations of nearby late M dwarfs.Comment: 27 pages, 11 figure
Three Warm Jupiters around Solar-analog Stars Detected with TESS*
We report the discovery and characterization of three giant exoplanets orbiting solar-analog stars, detected by the TESS space mission and confirmed through ground-based photometry and radial velocity measurements taken at La Silla observatory with FEROS. TOI-2373 b is a warm Jupiter orbiting its host star every âŒ13.3 days, and is one of the most massive known exoplanet with a precisely determined mass and radius around a star similar to the Sun, with an estimated mass of m _p = and a radius of r _p = . With a mean density of , TOI-2373 b is among the densest planets discovered so far. TOI-2416 b orbits its host star on a moderately eccentric orbit with a period of âŒ8.3 days and an eccentricity of e = . TOI-2416 b is more massive than Jupiter with m _p = , however is significantly smaller with a radius of r _p = , leading to a high mean density of . TOI-2524 b is a warm Jupiter near the hot Jupiter transition region, orbiting its star every âŒ7.2 days on a circular orbit. It is less massive than Jupiter with a mass of m _p = , and is consistent with an inflated radius of r _p = , leading to a low mean density of . The newly discovered exoplanets TOI-2373 b, TOI-2416 b, and TOI-2524 b have estimated equilibrium temperatures of K, K, and K, respectively, placing them in the sparsely populated transition zone between hot and warm Jupiters
Radial drift and concurrent ablation of boulder-sized objects
Context. The composition of a protoplanetary disk at a given location does not only depend on temperature and pressure but also on the time dependent transport of matter, such as radial drift of solid bodies, which could release water and other volatile species before disintegration or accretion onto a larger body with potentially considerable implications for the composition of planets.
Aims. We performed a parameter study focused on the water depletion of different sized bodies able to cross the water snowline by gas-induced radial drift.
Methods. Either the analytical HertzâKnudsenâLangmuir sublimation formula assuming equilibrium temperature within the body or a more involved, numerical model for the internal thermal evolution was coupled with an α-disk model. Different properties of the disk and the embedded body were explored.
Results. Bodies with radii up to 100 m drift faster toward the central star than the water snowline, and can therefore cross it. The region that can be reached before complete disintegration â and is therefore polluted with HâO ice â extends to 10% closer to the star than the snowline location. The extent of this polluted region could be multiple times larger in the presence of a dust mantle, which is, however, unlikely to form due to frequent collisions with objects smaller than a centimeter.
Conclusions. Given a significant abundance of meter-sized boulders in protoplanetary disks, the transport of water by radial drift of these bodies toward regions closer to the star than the snowline is not negligible and this flux of volatiles can be estimated for a given distribution of solid body sizes and compositions. A simple expression for surface sublimation is applicable for a homogeneous body consisting of only dust and water ice without a dust mantle