Growth of Jupiter: Enhancement of core accretion by a voluminous low-mass envelope (original) (raw)
Related papers
The formation of Jupiter’s diluted core by a giant impact
Nature
The Juno mission 1 is designed to measure Jupiter's gravitational field with an extraordinary precision 2. Structure models of Jupiter that fit Juno gravity data suggest that Jupiter could have a diluted core and a total heavy-element mass M Z ranging from ten to two dozens of Earth masses (∼ 10 − 24M ⊕). In that case the heavy elements are distributed within an extended region with a size of nearly half of Jupiter's radius R J 3, 4. Planet formation models indicate that most of the heavy elements are accreted onto a compact core 5-7 , and that almost no solids are accreted during runaway gas accretion (mainly hydrogen and helium, hereafter H-He), regardless to whether the accreted solids are planetesimals or pebbles 8-10. Therefore, the inferred heavy-element mass in the planet cannot significantly exceeds the core's mass. The fact that Jupiter's core could be diluted, and yet, the estimated total heavy-element mass in the planet is relatively large challenges planet formation theory. A possible explanation is erosion of the compact heavy-element core. Its efficiency, however, is uncertain and depends on both the immiscibility of heavy materials in metallic hydrogen and the efficiency 1
EMBRYO IMPACTS AND GAS GIANT MERGERS. I. DICHOTOMY OF JUPITER AND SATURN's CORE MASS
The Astrophysical Journal, 2010
Interior to the gaseous envelopes of Saturn, Uranus, and Neptune, there are high-density cores with masses larger than 10 Earth masses. According to the conventional sequential accretion hypothesis, such massive cores are needed for the onset of efficient accretion of their gaseous envelopes. However, Jupiter's gaseous envelope is more massive and core may be less massive than those of Saturn. In order to account for this structural diversity and the super-solar metallicity in the envelope of Jupiter and Saturn, we investigate the possibility that they may have either merged with other gas giants or consumed several Earth-mass proto-planetary embryos during or after the rapid accretion of their envelope. In general, impinging sub-Earth-mass planetesimals disintegrate in gas giants' envelopes deposit heavy elements well outside the cores and locally suppress the convection. Consequently, their fragments sediment to promote the growth of cores. Through a series of numerical simulations, we show that it is possible for colliding super-Earth-mass embryos to reach the cores of gas giants. Direct parabolic collisions also lead to the coalescence of gas giants and merging of their cores. In these cases, the energy released from the impact leads to vigorous convective motion throughout the envelope and the erosion of the cores. This dichotomy contributes to the observed dispersion in the internal structure and atmospheric composition between Jupiter and Saturn and other gas giant planets and elsewhere.
CAPTURE AND EVOLUTION OF PLANETESIMALS IN CIRCUMJOVIAN DISKS
We study the evolution of planetesimals in evolved gaseous disks that orbit a solar-mass star and harbor a Jupitermass planet at a 5 p ≈ AU. The gas dynamics are modeled with a three-dimensional hydrodynamics code that employs nested grids and achieves a resolution of one Jupiter radius in the circumplanetary disk. The code models solids as individual particles. Planetesimals are subjected to gravitational forces by the star and the planet, a drag force by the gas, disruption via ram pressure, and mass loss through ablation. The mass evolution of solids is calculated self-consistently with their temperature, velocity, and position. We consider icy and icy/rocky bodies of radius 0.1-100 km, initially deployed on orbits around the star within a few Hill radii (R H) of the planetʼs orbit. Planetesimals are scattered inward, outward, and toward disk regions of radius r a p ≫. Scattering can relocate significant amounts of solids, provided that regions r a 3 p | − | ∼ R H are replenished with planetesimals. Scattered bodies can be temporarily captured on planetocentric orbits. Ablation consumes nearly all solids at gas temperatures 220 ≳ K. Super-Keplerian rotation around and beyond the outer edge of the gas gap can segregate 0.1 km ≲ bodies, producing solid gap edges at size-dependent radial locations. Capture, break-up, and ablation of solids result in a dust-laden circumplanetary disk with low surface densities of kilometer sized planetesimals, implying relatively long timescales for satellite formation. After a giant planet acquires most of its mass, accretion of solids is unlikely to significantly alter its heavy element content. The luminosity generated by accretion of solids and the contraction luminosity can be of similar orders of magnitude.
Formation of the giant planets
Planetary and Space Science, 1982
Observational constraints on interior models of the giant planets indicate that these planets were all much hotter when they formed and they all have rock and/or ice cores of ten to thirty earth masses. These cores are probably soluble in the envelopes above, especially in Jupiter and Saturn, and are therefore likely to be primordial. They persist despite the continual upward mixing by thermally driven convection throughout the age of the solar system, because of the inefficiency of double-diffusive convection. Thus, these planets most probably formed by the hydrodynamic collapse of a gaseous envelope onto a core rather than by direct instability of the gaseous solar nebula. Recent calculations by Mizuno (1980, Prog. Theor. Phys. 64, 544) show that this formation mechanism may explain the similarity of giant planet core masses. Problems remain however, and no current model is entirely satisfactory in explaining the properties of the giant planets and simultaneously satisfying the terrestrial planet constraints. Satellite systematics and protoplanetary disk nebulae are also discussed and related to formation conditions.
Arxiv preprint arXiv: …, 2010
We review the current theoretical understanding how growth from micrometer sized dust to massive giant planets occurs in disks around young stars. After introducing a number of observational constraints from the solar system, from observed protoplanetary disks, and from the extrasolar planets, we simplify the problem by dividing it into a number of discrete stages which are assumed to occur in a sequential way. In the first stage -the growth from dust to kilometer sized planetesimals -the aerodynamics of the bodies are of central importance. We discuss both a purely coagulative growth mode, as well as a gravoturbulent mode involving a gravitational instability of the dust. In the next stage, planetesimals grow to protoplanets of roughly 1000 km in size. Gravity is now the dominant force. The mass accretion can be strongly non-linear, leading to the detachment of a few big bodies from the remaining planetesimals. In the outer planetary system (outside a few AU), some of these bodies can become so massive that they eventually accrete a large gaseous envelope. This is the stage of giant planet formation, as understood within the core accretiongas capture paradigm. We also discuss the direct gravitational collapse model where giant planets are thought to form directly via a gravitational fragmentation of the gas disk. In the inner system, protoplanets collide in the last stage -probably after the dispersal of the gaseous disk -in giant impacts until the separations between the remaining terrestrial planets become large enough to allow long term stability. We finish the review with some selected questions.
Gaseous drag and planetary formation by accretion
Icarus, 1985
We have made numerical experiments of the collisional and gravitational interaction of a planetesimal swarm in the early Solar System. In particular we study the dynamical evolution of an initial population of kilometer-size planetesimals subject to collisions (accretion, rebound, cratering, and catastrophic fragmentation). This study is based on a Monte-Carlo statistical method and provides the mass and velocity distributions of the planetesimal swarm as a function of time as well as their distribution in heliocentric distance. Several experiments have been performed and three of them are presented here. They simulate the accretional growth of numerous planetesimals in the absence (or presence) of gaseous drag, with (or without) one larger embryo among them, and with (or without) a size gradient. The results show that (i) for a population of planetesimals submitted to a negative gradient in size as the heliocentric distance increases, the outer planetesimals spiral toward the Sun faster than inner ones, leading after some time to an accumulation of bodies inside the cloud which allows the formation of an embryo; (ii) the growth of one embryo among a population of planetesimals is accelerated by the presence of gas and is warranted as long as its feeding zone is fed by the inward flow of planetesimals due to gas drag. These results offer some complementary new insights in the understanding of the accretional formation of 4-5 terrestrial planets instead of the numerous Moon-size planets generally found in numerical experiments.
On the formation of terrestrial planets in hot-Jupiter systems
Astronomy & Astrophysics, 2007
"Context. There are numerous extrasolar giant planets which orbit close to their central stars. These “hot-Jupiters” probably formed in the outer, cooler regions of their protoplanetary disks, and migrated inward to ∼0.1 AU. Since these giant planets must have migrated through their inner systems at an early time, it is uncertain whether they could have formed or retained terrestrial planets. Aims. We present a series of calculations aimed at examining how an inner system of planetesimals/protoplanets, undergoing terrestrial planet formation, evolves under the influence of a giant planet undergoing inward type II migration through the region bounded between 5–0.1 AU. Methods. We have previously simulated the effect of gas giant planet migration on an inner system protoplanet/planetesimal disk using a N-body code which included gas drag and a prescribed migration rate. We update our calculations here with an improved model that incorporates a viscously evolving gas disk, annular gap and inner-cavity formation due to the gravitational field of the giant planet, and self-consistent evolution of the giant’s orbit. Results. We find that 60% of the solids disk survives by being scattered by the giant planet into external orbits. Planetesimals are scattered outward almost as efficiently as protoplanets, resulting in the regeneration of a solids disk where dynamical friction is strong and terrestrial planet formation is able to resume. A simulation that was extended for a few Myr after the migration of the giant planet halted at 0.1 AU, resulted in an apparently stable planet of ∼2 m⊕ forming in the habitable zone. Migration–induced mixing of volatile-rich material from beyond the “snowline” into the inner disk regions means that terrestrial planets that form there are likely to be water-rich. Conclusions. We predict that hot-Jupiter systems are likely to harbor water-abundant terrestrial planets in their habitable zones. These planets may be detected by future planet search missions."
Dynamics and accretion of planetesimals
Progress of Theoretical and Experimental Physics, 2012
In the standard scenario of planet formation, planets are formed from a protoplanetary disk that consists of gas and dust. The building blocks of solid planets are called planetesimals; they are formed by coagulation of dust. We review the basic dynamics and accretion of planetesimals by showing N-body simulations. The orbits of planetesimals evolve through two-body gravitational relaxation: viscous stirring increases the random velocity and dynamical friction realizes the equiparation of the random energy. In the early stage of planetesimal accretion, the growth mode of planetesimals is runaway growth, where larger planetesimals grow faster than smaller ones. When a protoplanet (a runaway-growing planetesimal) exceeds a critical mass, the growth mode shifts to oligarchic growth, where similar-sized protoplanets grow while keeping a certain orbital separation. The final stage of terrestrial planet formation is collision among protoplanets, known as giant impacts. We also summarize the dynamical effects of disk gas on planets and the core accretion model for the formation of gas giants, and discuss the diversity of planetary systems.
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.
Accumulation and migration of the bodies from the zones of giant planets
Earth, Moon and Planets, 1987
Within the model of solid-body accumulation of planets (or their nuclei) the accumulation and migration of bodies from the feeding zones of the giant planets are investigated. The investigation is based on results of computer simulation of evolving disks which initially consisted of hundreds of particles moving about the Sun and coagulating under collisions. In some models the disks initially consisted of identical bodies. In other models they included also almost-formed planets. The computer simulation results as well as analytical investigations of the disk evolution depending on the number of particles in the disk allowed some estimates and conclusions on the accumulation process when the number of initial bodies was great (-106-lOI*). In this paper the characteristics of an initial protoplanetary circumsolar cloud, the body migration in the forming solar system, the planet orbit evolution, the formation of the beyond-Neptune belt and asteroid belts between the giant planet orbits are considered. The results obtained confirm many analytical estimates earlier made by V. S. Safronov and his colleagues.