The Formation and Architecture of Young Planetary Systems (original) (raw)
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Formation, Orbital and Internal Evolutions of Young Planetary Systems
Space Science Reviews, 2016
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. Keywords planets and satellites: formation • planets and satellites: interiors • protoplanetary disks • planet-disk interactions 1 Introduction Planet formation and evolution is a fast-moving field, stimulated by the rapid increase in the number of exoplanets and their great diversity. Despite the wealth of observational data on planetary systems, including our own, it is difficult to have a general theory for planet formation and evolution as it involves a broad range of physical processes that happen at
Characterization of exoplanets from their formation
Astronomy & Astrophysics, 2012
A first characterization of extrasolar planets by the observational determination of the radius has recently been achieved for a large number of planets. For some planets, a measurement of the luminosity has also been possible, with many more directly imaged planets expected in the near future. The statistical characterization of exoplanets through their mass-radius and mass-luminosity diagram is becoming possible. This is for planet formation and evolution theory of similar importance as the mass-distance diagram. Aims. Our aim is to extend our planet formation model into a coupled formation and evolution model. We want to calculate from one single model in a self-consistent way all basic quantities describing a planet: its mass, semimajor axis, composition, radius and luminosity. We then want to use this model for population synthesis calculations. Methods. In this and a companion paper, we show how we solve the structure equations describing the gaseous envelope of a protoplanet not only during the early formation phase, but also during the gas runaway accretion phase, and during the evolutionary phase at constant mass on Gyr timescales. We improve the model further with a new prescription for the disk-limited gas accretion rate, an internal structure model for the planetary core assuming a differentiated interior, and the inclusion of radioactive decay as an additional heat source in the core. Results. We study the in situ formation and evolution of Jupiter, the mass-radius relationship of giant planets, the influence of the core mass on the radius and the luminosity both in the "hot start" and the "cold start" scenario. We put special emphasis on the validation of the model by comparison with other models of planet formation and evolution. We find that our results agree very well with those of more complex models, despite a number of simplifications we make in our calculations.
2013
Aims. We explore the relations between physical and orbital properties of planets and properties of their host stars to identify the main observable signatures of the formation and evolution processes of planetary systems. Methods. We used a large sample of FGK dwarf planet-hosting stars with stellar parameters derived in a homogeneous way from the SWEET-Cat database to study the relation between stellar metallicity and position of planets in the period-mass diagram. We then used all the radial-velocity-detected planets orbiting FGK stars to explore the role of planet-disk and planet-planet interaction on the evolution of orbital properties of planets with masses above 1M Jup. Results. Using a large sample of FGK dwarf hosts we show that planets orbiting metal-poor stars have longer periods than those in metal-rich systems. This trend is valid for masses at least from ≈10M ⊕ to ≈4M Jup. Earth-like planets orbiting metal-rich stars always show shorter periods (fewer than 20 days) than those orbiting metal-poor stars. However, in the short-period regime there are a similar number of planets orbiting metal-poor stars. We also found statistically significant evidence that very high mass giants (with a mass higher than 4M Jup) have on average more eccentric orbits than giant planets with lower mass. Finally, we show that the eccentricity of planets with masses higher than 4M Jup tends to be lower for planets with shorter periods. Conclusions. Our results suggest that the planets in the P-M P diagram are evolving differently because of a mechanism that operates over a wide range of planetary masses. This mechanism is stronger or weaker depending on the metallicity of the respective system. One possibility is that planets in metal-poor disks form farther out from their central star and/or they form later and do not have time to migrate as far as the planets in metal-rich systems. The trends and dependencies obtained for very high mass planetary systems suggest that planet-disk interaction is a very important and orbit-shaping mechanism for planets in the high-mass domain.
Observed Properties of Exoplanets: Masses, Orbits, and Metallicities
Progress of Theoretical Physics Supplement, 2005
We review the observed properties of exoplanets found by the Doppler technique that has revealed 152 planets to date. We focus on the ongoing 18-year survey of 1330 FGKM type stars at Lick, Keck, and the Anglo-Australian Telescopes that offers both uniform Doppler precision (3 m s −1 ) and long duration. The 104 planets detected in this survey have minimum masses (M sin i) as low as 6 M Earth , orbiting between 0.02 and 6 AU. The core-accretion model of planet formation is supported by four observations: 1) The mass distribution rises toward the lowest detectable masses, dN /dM ∝ M −1.0 . 2) Stellar metallicity correlates strongly with the presence of planets. 3) One planet (1.3 MSat) has a massive rocky core, MCore ≈ 70 M Earth . 4) A super-Earth of ∼ 7 M Earth has been discovered. The distribution of semi-major axes rises from 0.3 -3.0 AU (dN /d log a) and extrapolation suggests that ∼12% of the FGK stars harbor gas-giant exoplanets within 20 AU. The median orbital eccentricity is e = 0.25, and even planets beyond 3 AU reside in eccentric orbits, suggesting that the circular orbits in our Solar System are unusual. The occurrence "hot Jupiters" within 0.1 AU of FGK stars is 1.2±0.2%. Among stars with one planet, 14% have at least one additional planet, occasionally locked in resonances. Kepler and COROT will measure the occurrence of earth-sized planets. The Space Interferometry Mission (SIM) will detect planets with masses as low as 3 M Earth orbiting within 2 AU of stars within 10 pc, and it will measure masses, orbits, and multiplicity. The candidate rocky planets will be amenable to follow-up spectroscopy by the "Terrestrial Planet Finder" and Darwin.
Planet formation: The case for large efforts on the computational side
arXiv: Earth and Planetary Astrophysics, 2019
Modern astronomy has finally been able to observe protoplanetary disks in reasonable resolution and detail, unveiling the processes happening during planet formation. These observed processes are understood under the framework of disk-planet interaction, a process studied analytically and modeled numerically for over 40 years. Long a theoreticians' game, the wealth of observational data has been allowing for increasingly stringent tests of the theoretical models. Modeling efforts are crucial to support the interpretation of direct imaging analyses, not just for potential detections but also to put meaningful upper limits on mass accretion rates and other physical quantities in current and future large-scale surveys. This white paper addresses the questions of what efforts on the computational side are required in the next decade to advance our theoretical understanding, explain the observational data, and guide new observations. We identified the nature of accretion, ab initio p...
Terrestrial Planet Formation in Exoplanetary Systems
2008
Many giant exoplanets are thought to have formed in the outer regions of a protoplanetary disk, and to have then migrated close to the central star. Hence, it is uncertain whether terrestrial planets can grow and be retained in these `hot-Jupiter' systems. Previous speculations, based on the assumption that migrating giant planets will clear planet-forming material from their swept zone, have concluded that such systems should lack terrestrial planets. This thesis presents a succession of four planet formation models, of increasing sophistication, aimed at examining how an inner system of solid bodies, undergoing terrestrial planet formation, evolves under the inuence of a giant planet undergoing inward type II migration. Protoplanetary growth is handled by an N+N'-body code, capable of simulating the accretion of a two-phase protoplanetplanetesimal population, and tracking their volatiles content. Gas dynamics and related dissipative processes are calculated with a linked viscous gas disk algorithm capable of simulating: gas accretion onto the central star and photoevaporation; type II migration of the giant planet; type I migration of protoplanets; and the effect of gas drag on planetesimals. In all simulations, a large fraction of the inner system material survives the passage of the giant, either by accreting into massive planets shepherded inward of the giant (reminiscent of the short-period `hot-Earths' discovered recently), or by being scattered into external orbits. Typically, sufcient mass is scattered outward to provide for the eventual accretion of a set of terrestrial planets in external orbits. The results of this thesis lead to the prediction that hot-Jupiter systems are likely to harbor water-rich terrestrial planets in their habitable zones and hot-Earths may also be present. These planets may be detected by future planet search missions.
Theory of planet formation and comparison with observation
EPJ Web of Conferences, 2011
The planetary mass-radius diagram is an observational result of central importance to understand planet formation. We present an updated version of our planet formation model based on the core accretion paradigm which allows us to calculate planetary radii and luminosities during the entire formation and evolution of the planets. We first study with it the formation of Jupiter, and compare with previous works. Then we conduct planetary population synthesis calculations to obtain a synthetic mass-radius diagram which we compare with the observed one. Except for bloated Hot Jupiters which can be explained only with additional mechanisms related to their proximity to the star, we find a good agreement of the general shape of the observed and the synthetic M − R diagram. This shape can be understood with basic concepts of the core accretion model.
Probing structural and evolutionary properties of exoplanets
Memorie Della Societa Astronomica Italiana, 2009
We summarise the results of a) a Keck/HIRES Doppler search for planets orbiting metal-poor dwarfs, and b) a new spectroscopic and photometric analysis of the transiting planet systems TrES-3 and TrES-4. These two experiments have allowed us to address important issues related to the correlation between planet frequencies and properties and the metallicity of the hosts. Our results can usefully inform formation, structural, and evolutionary models of gas giant planets.