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Anders Johansen - One of the best experts on this subject based on the ideXlab platform.
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The fate of Planetesimals formed at planetary gap edges
arXiv: Earth and Planetary Astrophysics, 2020Co-Authors: L.e.j. Eriksson, T. Ronnet, Anders JohansenAbstract:The presence of rings and gaps in protoplanetary discs are often ascribed to planet-disc interactions, where dust and pebbles are trapped at the edges of planetary induced gas gaps. Recent work has shown that these are likely sites for Planetesimal formation via the streaming instability. Given the large amount of Planetesimals that potentially form at gap edges, we address the question of their fate and ability to radially transport solids in protoplanetary discs. We perform a series of N-body simulations of Planetesimal orbits, taking into account the effect of gas drag and mass loss via ablation. We consider two planetary systems: one akin to the young Solar System, and another one inspired by HL Tau. In both systems, the close proximity to the gap-opening planets results in large orbital excitations, causing the Planetesimals to leave their birth locations and spread out across the disc soon after formation. Planetesimals that end up on eccentric orbits interior of 10au experience efficient ablation, and lose all mass before they reach the innermost disc region. In our nominal Solar System simulation with $\dot{M}_0=10^{-7}\, M_{\odot}\, \textrm{yr}^{-1}$ and $\alpha=10^{-2}$, we find that 70% of the initial Planetesimal mass has been ablated after 500kyr. The ablation rate in HL Tau is lower, and only 11% of the initial Planetesimal mass has been ablated after 1Myr. The ablated material consist of a mixture of solid grains and vaporized ices, where a large fraction of the vaporized ices re-condense to form solid ice. Assuming that the solids grow to pebbles in the disc midplane, the total integrated mass that reaches 1au is $15\, M_{\oplus}$ in the nominal Solar System simulation and $25\, M_{\oplus}$ in the nominal HL Tau simulation. Our results demonstrate that scattered Planetesimals can carry a significant flux of solids past planetary-induced gaps in protoplanetary discs.
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growth after the streaming instability from Planetesimal accretion to pebble accretion
Astronomy and Astrophysics, 2019Co-Authors: Beibei Liu, C W Ormel, Anders JohansenAbstract:Context. Streaming instability is a key mechanism in planet formation, clustering pebbles into Planetesimals with the help of self-gravity. It is triggered at a particular disk location where the local volume density of solids exceeds that of the gas. After their formation, Planetesimals can grow into protoplanets by feeding from other Planetesimals in the birth ring as well as by accreting inwardly drifting pebbles from the outer disk.Aims. We aim to investigate the growth of Planetesimals into protoplanets at a single location through streaming instability. For a solar-mass star, we test the conditions under which super-Earths are able to form within the lifetime of the gaseous disk.Methods. We modified the Mercury N-body code to trace the growth and dynamical evolution of a swarm of Planetesimals at a distance of 2.7 AU from the star. The code simulates gravitational interactions and collisions among Planetesimals, gas drag, type I torque, and pebble accretion. Three distributions of Planetesimal sizes were investigated: (i) a mono-dispersed population of 400 km radius Planetesimals, (ii) a poly-dispersed population of Planetesimals from 200 km up to 1000 km, (iii) a bimodal distribution with a single runaway body and a swarm of smaller, 100 km size Planetesimals.Results. The mono-dispersed population of 400 km size Planetesimals cannot form protoplanets of a mass greater than that of the Earth. Their eccentricities and inclinations are quickly excited, which suppresses both Planetesimal accretion and pebble accretion. Planets can form from the poly-dispersed and bimodal distributions. In these circumstances, it is the two-component nature that damps the random velocity of the large embryo through the dynamical friction of small Planetesimals, allowing the embryo to accrete pebbles efficiently when it approaches 10−2 M⊕. Accounting for migration, close-in super-Earth planets form. Super-Earth planets are likely to form when the pebble mass flux is higher, the disk turbulence is lower, or the Stokes number of the pebbles is higher.Conclusions. For the single site Planetesimal formation scenario, a two-component mass distribution with a large embryo and small Planetesimals promotes planet growth, first by Planetesimal accretion and then by pebble accretion of the most massive protoplanet. Planetesimal formation at single locations such as ice lines naturally leads to super-Earth planets by the combined mechanisms of Planetesimal accretion and pebble accretion. (Less)
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growth after the streaming instability from Planetesimal accretion to pebble accretion
arXiv: Earth and Planetary Astrophysics, 2019Co-Authors: Beibei Liu, C W Ormel, Anders JohansenAbstract:Streaming instability is a key mechanism in planet formation, clustering pebbles into Planetesimals. It is triggered at a particular disk location where the local volume density of solids exceeds that of the gas. After their formation, Planetesimals can grow by feeding from other Planetesimals in the birth ring as well as by accreting inwardly drifting pebbles from the outer disk. To investigate the growth of Planetesimals at a single location by the streaming instability, we test the conditions under which super-Earths are able to form within the lifetime of the gaseous disk. We modify the \texttt{Mercury} N-body code to trace the growth and dynamical evolution of a swarm of Planetesimals at the ice line for a solar-mass star. Three distributions of Planetesimal sizes are investigated: (i) a mono-dispersed population of 400 km radius Planetesimals, (ii) a poly-dispersed populations of Planetesimals from 200 km up to 1000 km, (iii) a bimodal distribution with a single runaway body and a swarm of smaller, 100 km size Planetesimals. The mono-disperse population of 400 km size Planetesimals cannot form $\gtrsim$ Earth mass protoplanets. Their velocity dispersions are quickly excited, which suppresses both Planetesimal and pebble accretion. Planets can form from the poly-dispersed and bimodal distributions. In these circumstances, the two-component nature damps the random velocity of the large embryo by small Planetesimals' dynamical friction, allowing the embryo to accrete pebbles efficiently when it approaches $10^{-2}$ Earth mass. We find that super-Earth planets are preferred to form when the pebble mass flux is higher, the disk turbulence is lower, or the Stokes number of the pebbles is higher.
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Debris disc constraints on Planetesimal formation
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: Alexander V. Krivov, Anders Johansen, Aljoscha Ide, Torsten Löhne, Jürgen BlumAbstract:Two basic routes for Planetesimal formation have been proposed over the last decades. One is a classical 'slow-growth' scenario. Another one is particle concentration models, in which small pebbles are concentrated locally and then collapse gravitationally to form Planetesimals. Both types of models make certain predictions for the size spectrum and internal structure of newly born Planetesimals. We use these predictions as input to simulate collisional evolution of debris discs left after the gas dispersal. The debris disc emission as a function of a system's age computed in these simulations is compared with several Spitzer and Herschel debris disc surveys around A-type stars. We confirm that the observed brightness evolution for the majority of discs can be reproduced by classical models. Further, we find that it is equally consistent with the size distribution of Planetesimals predicted by particle concentrationmodels - provided the objects are loosely bound 'pebble piles' as thesemodels also predict. Regardless of the assumed Planetesimal formation mechanism, explaining the brightest debris discs in the samples uncovers a 'disc mass problem'. To reproduce such discs by collisional simulations, a total mass of Planetesimals of up to ~1000 Earth masses is required, which exceeds the total mass of solids available in the protoplanetary progenitors of debris discs. This may indicate that stirring was delayed in some of the bright discs, that giant impacts occurred recently in some of them, that some systems may be younger than previously thought or that non-collisional processes contribute significantly to the dust production. (Less)
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Planetesimal formation by the streaming instability in a photoevaporating disk
The Astrophysical Journal, 2017Co-Authors: Daniel Carrera, Anders Johansen, Uma Gorti, Melvyn B. DaviesAbstract:Recent years have seen growing interest in the streaming instability as a candidate mechanism to produce Planetesimals. However, these investigations have been limited to small-scale simulations. We now present the results of a global protoplanetary disk evolution model that incorporates Planetesimal formation by the streaming instability, along with viscous accretion, photoevaporation by EUV, FUV, and X-ray photons, dust evolution, the water ice line, and stratified turbulence. Our simulations produce massive (60-130 $M_\oplus$) Planetesimal belts beyond 100 au and up to $\sim 20 M_\oplus$ of Planetesimals in the middle regions (3-100 au). Our most comprehensive model forms 8 $M_\oplus$ of Planetesimals inside 3 au, where they can give rise to terrestrial planets. The Planetesimal mass formed in the inner disk depends critically on the timing of the formation of an inner cavity in the disk by high-energy photons. Our results show that the combination of photoevaporation and the streaming instability are efficient at converting the solid component of protoplanetary disks into Planetesimals. Our model, however, does not form enough early Planetesimals in the inner and middle regions of the disk to give rise to giant planets and super-Earths with gaseous envelopes. Additional processes such as particle pileups and mass loss driven by MHD winds may be needed to drive the formation of early Planetesimal generations in the planet forming regions of protoplanetary disks.
Philip J. Armitage - One of the best experts on this subject based on the ideXlab platform.
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turbulence regulates the rate of Planetesimal formation via gravitational collapse
arXiv: Earth and Planetary Astrophysics, 2020Co-Authors: Daniel A Gole, Jacob B. Simon, Andrew N. Youdin, Philip J. ArmitageAbstract:We study how the interaction between the streaming instability and intrinsic gas-phase turbulence affects Planetesimal formation via gravitational collapse. Turbulence impedes the formation of dense particle clumps by acting as an effective turbulent diffusivity, but it can also promote Planetesimal formation by concentrating solids, for example in zonal flows. We quantify the effect of turbulent diffusivity using numerical simulations of the streaming instability in small local domains, forced with velocity perturbations that establish approximately Kolmogorov-like fluid turbulence. We find that Planetesimal formation is strongly suppressed by turbulence once velocity fluctuations exceed a threshold value of $\delta v^2 \simeq 10^{-3.5} - 10^{-3} c_s^2$. Turbulence whose strength is just below the threshold reduces the rate of solid material being converted into bound clumps. The main effect of turbulence is to thicken the mid-plane solid layer. Our results are thus consistent with Planetesimal formation requiring a mid-plane solid-to-gas ratio $\epsilon \gtrsim 0.5$. We describe a method for tracking bound clumps in our simulations, and use this method to construct a mass function of Planetesimals that is measured for each clump shortly after its collapse. Adopting this definition of the initial mass, instead of measuring masses at a fixed time, reduces Planetesimal masses by a factor of three. For models in which Planetesimals form, we show that the initial mass function is well-described by a broken power law, whose parameters are robust to the inclusion and strength of imposed turbulence. Turbulence in protoplanetary disks is likely to substantially exceed the threshold for Planetesimal formation at radii where temperatures $T \gtrsim 10^3 \ {\rm K}$ lead to thermal ionization. Fully in situ Planetesimal and planet formation may therefore not be viable for the closest-in exoplanets.
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implications of the interstellar object 1i oumuamua for planetary dynamics and Planetesimal formation
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: Sean N. Raymond, Philip J. Armitage, Dimitri Veras, Elisa V. Quintana, Thomas BarclayAbstract:'Oumuamua, the first bona-fide interstellar Planetesimal, was discovered passing through our Solar System on a hyperbolic orbit. This object was likely dynamically ejected from an extrasolar planetary system after a series of close encounters with gas giant planets. To account for 'Oumuamua's detection, simple arguments suggest that ~1 Earth-mass of Planetesimals are ejected per Solar mass of Galactic stars. However, that value assumes mono-sized Planetesimals. If the Planetesimal mass distribution is instead top-heavy the inferred mass in interstellar Planetesimals increases to an implausibly high value. The tension between theoretical expectations for the Planetesimal mass function and the observation of 'Oumuamua can be relieved if a small fraction (~1%) of Planetesimals are tidally disrupted on the pathway to ejection into 'Oumuamua-sized fragments. Using a large suite of simulations of giant planet dynamics including Planetesimals, we confirm that roughly 1% of Planetesimals pass within the tidal disruption radius of a gas giant on their pathway to ejection. 'Oumuamua may thus represent a surviving fragment of a disrupted Planetesimal. Finally, we argue that an asteroidal composition is dynamically disfavoured for 'Oumuamua, as asteroidal Planetesimals are both less abundant and ejected at a lower efficiency than cometary Planetesimals.
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interstellar object oumuamua as an extinct fragment of an ejected cometary Planetesimal
The Astrophysical Journal, 2018Co-Authors: Sean N. Raymond, Philip J. Armitage, Dimitri VerasAbstract:'Oumuamua was discovered passing through our solar system on a hyperbolic orbit. It presents an apparent contradiction, with colors similar to those of volatile-rich solar system bodies but with no visible outgassing or activity during its close approach to the Sun. Here, we show that this contradiction can be explained by the dynamics of Planetesimal ejection by giant planets. We propose that 'Oumuamua is an extinct fragment of a comet-like Planetesimal born a planet-forming disk that also formed Neptune- to Jupiter-mass giant planets. On its pathway to ejection 'Oumuamua's parent body underwent a close encounter with a giant planet and was tidally disrupted into small pieces, similar to comet Shoemaker–Levy 9's disruption after passing close to Jupiter. We use dynamical simulations to show that 0.1%–1% of cometary Planetesimals undergo disruptive encounters prior to ejection. Rocky asteroidal Planetesimals are unlikely to disrupt due to their higher densities. After disruption, the bulk of fragments undergo enough close passages to their host stars to lose their surface volatiles and become extinct. Planetesimal fragments such as 'Oumuamua contain little of the mass in the population of interstellar objects but dominate by number. Our model makes predictions that will be tested in the coming decade by the Large Synoptic Survey Telescope.
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Implications of the interstellar object 1I/'Oumuamua for planetary dynamics and Planetesimal formation
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: Sean N. Raymond, Philip J. Armitage, Dimitri Veras, Elisa V. Quintana, Thomas BarclayAbstract:'Oumuamua, the first bona-fide interstellar Planetesimal, was discovered passing through our Solar System on a hyperbolic orbit. This object was likely dynamically ejected from an extrasolar planetary system after a series of close encounters with gas giant planets. To account for 'Oumuamua's detection, simple arguments suggest that ~1 Earth-mass of Planetesimals are ejected per Solar mass of Galactic stars. However, that value assumes mono-sized Planetesimals. If the Planetesimal mass distribution is instead top-heavy the inferred mass in interstellar Planetesimals increases to an implausibly high value. The tension between theoretical expectations for the Planetesimal mass function and the observation of 'Oumuamua can be relieved if a small fraction (~1%) of Planetesimals are tidally disrupted on the pathway to ejection into 'Oumuamua-sized fragments. Using a large suite of simulations of giant planet dynamics including Planetesimals, we confirm that roughly 1% of Planetesimals pass within the tidal disruption radius of a gas giant on their pathway to ejection. 'Oumuamua may thus represent a surviving fragment of a disrupted Planetesimal. Finally, we argue that an asteroidal composition is dynamically disfavoured for 'Oumuamua, as asteroidal Planetesimals are both less abundant and ejected at a lower efficiency than cometary Planetesimals.
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Interstellar object 'Oumuamua as an extinct fragment of an ejected cometary Planetesimal
The Astrophysical journal letters, 2018Co-Authors: Sean N. Raymond, Philip J. Armitage, Dimitri VerasAbstract:Oumuamua was discovered passing through our Solar System on a hyperbolic orbit. It presents an apparent contradiction, with colors similar to those of volatile-rich Solar System bodies but with no visible outgassing or activity during its close approach to the Sun. Here we show that this contradiction can be explained by the dynamics of Planetesimal ejection by giant planets. We propose that 'Oumuamua is an extinct fragment of a comet-like Planetesimal born in a planet-forming disk that also formed Neptune- to Jupiter-mass giant planets. On its pathway to ejection 'Oumuamua's parent body underwent a close encounter with a giant planet and was tidally disrupted into small pieces, similar to comet Shoemaker-Levy 9's disruption after passing close to Jupiter. We use dynamical simulations to show that 0.1-1% of cometary Planetesimals undergo disruptive encounters prior to ejection. Rocky asteroidal Planetesimals are unlikely to disrupt due to their higher densities. After disruption, the bulk of fragments undergo enough close passages to their host stars to lose their surface volatiles and become extinct. Planetesimal fragments such as 'Oumuamua contain little of the mass in the population of interstellar objects but dominate by number. Our model makes predictions that will be tested in the coming decade by LSST.
Roman R. Rafikov - One of the best experts on this subject based on the ideXlab platform.
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planet formation in stellar binaries i Planetesimal dynamics in massive protoplanetary disks
The Astrophysical Journal, 2014Co-Authors: Roman R. Rafikov, Kedron SilsbeeAbstract:About 20% of exoplanets discovered by radial velocity surveys reside in stellar binaries. To clarify their origin one has to understand the dynamics of Planetesimals in protoplanetary disks within binaries. The standard description, accounting for only gas drag and gravity of the companion star, has been challenged recently, as the gravity of the protoplanetary disk was shown to play a crucial role in Planetesimal dynamics. An added complication is the tendency of protoplanetary disks in binaries to become eccentric, giving rise to additional excitation of Planetesimal eccentricity. Here, for the first time, we analytically explore the secular dynamics of Planetesimals in binaries such as α Cen and γ Cep under the combined action of (1) gravity of the eccentric protoplanetary disk, (2) perturbations due to the (coplanar) eccentric companion, and (3) gas drag. We derive explicit solutions for the behavior of Planetesimal eccentricity e p in non-precessing disks (and in precessing disks in certain limits). We obtain the analytical form of the distribution of the relative velocities of Planetesimals, which is a key input for understanding their collisional evolution. Disk gravity strongly influences relative velocities and tends to push the sizes of Planetesimals colliding with comparable objects at the highest speed to small values, ~1 km. We also find that Planetesimals in eccentric protoplanetary disks apsidally aligned with the binary orbit collide at lower relative velocities than in misaligned disks. Our results highlight the decisive role that disk gravity plays in Planetesimal dynamics in binaries.
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planet formation in stellar binaries i Planetesimal dynamics in massive protoplanetary disks
arXiv: Earth and Planetary Astrophysics, 2014Co-Authors: Roman R. Rafikov, Kedron SilsbeeAbstract:About $20\%$ of exoplanets discovered by radial velocity surveys reside in stellar binaries. To clarify their origin one has to understand the dynamics of Planetesimals in protoplanetary disks within binaries. The standard description, accounting for only gas drag and gravity of the companion star has been challenged recently, as the gravity of the protoplanetary disk was shown to play a crucial role in Planetesimal dynamics. An added complication is the tendency of protoplanetary disks in binaries to become eccentric, giving rise to additional excitation of Planetesimal eccentricity. Here, for the first time, we analytically explore secular dynamics of Planetesimals in binaries such as $\alpha$ Cen and $\gamma$ Cep under the combined action of (1) gravity of the eccentric protoplanetary disk, (2) perturbations due to the (coplanar) eccentric companion, and (3) gas drag. We derive explicit solutions for the behavior of Planetesimal eccentricity ${\bf e}_p$ in non-precessing disks (and in precessing disks in certain limits). We obtain the analytical form of the distribution of relative velocities of Planetesimals, which is a key input for understanding their collisional evolution. Disk gravity strongly influences relative velocities and tends to push sizes of Planetesimals colliding with comparable objects at the highest speed to small values, $\sim 1$ km. We also find that Planetesimals in eccentric protoplanetary disks apsidally aligned with the binary orbit collide at lower relative velocities than in mis-aligned disks. Our results highlight a decisive role that disk gravity plays in Planetesimal dynamics in binaries.
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Effects of Planetesimal Dynamics on the Formation of Terrestrial Planets
arXiv: Astrophysics, 2003Co-Authors: Roman R. RafikovAbstract:Formation of terrestrial planets by agglomeration of Planetesimals in protoplanetary disks sensitively depends on the velocity evolution of Planetesimals. We describe a novel semi-analytical approach to the treatment of Planetesimal dynamics incorporating the gravitational scattering by massive protoplanetary bodies. Using this method we confirm that planets grow very slowly in the outer Solar System if gravitational scattering is the only process determining Planetesimal velocities, making it hard for giant planets to acquire their massive gaseous envelopes within less than 10 Myr. We put forward several possibilities for alleviating this problem.
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Dynamical evolution of Planetesimals in protoplanetary disks
The Astronomical Journal, 2003Co-Authors: Roman R. RafikovAbstract:The current picture of terrestrial planet formation relies heavily on our understanding of the dynamical evolution of Planetesimals -- asteroid-like bodies thought to be planetary building blocks. In this study we investigate the growth of eccentricities and inclinations of Planetesimals in spatially homogeneous protoplanetary disks using methods of kinetic theory. We explore disks with a realistic mass spectrum of Planetesimals evolving in time, similar to that obtained in self-consistent simulations of Planetesimal coagulation. We calculate the behavior of Planetesimal random velocities as a function of the Planetesimal mass spectrum both analytically and numerically; results obtained by the two approaches agree quite well. Scaling of random velocity with mass can always be represented as a combination of power laws corresponding to different velocity regimes (shear- or dispersion-dominated) of Planetesimal gravitational interactions. For different mass spectra we calculate analytically the exponents and time dependent normalizations of these power laws, as well as the positions of the transition regions between different regimes. It is shown that random energy equipartition between different Planetesimals can only be achieved in disks with very steep mass distributions (differential surface number density of Planetesimals falling off steeper than m^{-4}), or in the runaway tails. In systems with shallow mass spectra (shallower than m^{-3}) random velocities of small Planetesimals turn out to be independent of their masses. We also discuss the damping effects of inelastic collisions between Planetesimals and of gas drag, and their importance in modifying Planetesimal random velocities.
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Planetesimal Disk Evolution Driven by Planetesimal-Planetesimal Gravitational Scattering
The Astronomical Journal, 2003Co-Authors: Roman R. RafikovAbstract:We investigate the process of inhomogeneous Planetesimal disk evolution caused by Planetesimal-Planetesimal gravitational scattering. We develop a rather general approach based on kinetic theory that self-consistently describes the evolution in time and space of both the disk's surface density and its kinematic properties—dispersions of eccentricity and inclination. The gravitational scattering of Planetesimals is assumed to be in the dispersion-dominated regime, which considerably simplifies the analytical treatment. The resultant equations are of the advection-diffusion type. Distance-dependent scattering coefficients entering these equations are calculated analytically under the assumption of two-body scattering to leading order in the Coulomb logarithm. They are essentially nonlocal in nature. Our approach allows one to explore the dynamics of nonuniform Planetesimal disks with arbitrary mass and random-velocity distributions. It can also naturally include other physical mechanisms that are important for the evolution of such disks—gas drag, migration, and so on.
Debra A. Fischer - One of the best experts on this subject based on the ideXlab platform.
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Building massive compact Planetesimal disks from the accretion of pebbles
The Astrophysical Journal, 2015Co-Authors: John Moriarty, Debra A. FischerAbstract:We present a model in which Planetesimal disks are built from the combination of Planetesimal formation and accretion of radially drifting pebbles onto existing Planetesimals. In this model, the rate of accretion of pebbles onto Planetesimals quickly outpaces the rate of direct Planetesimal formation in the inner disk. This allows for the formation of a high mass inner disk without the need for enhanced Planetesimal formation or a massive protoplanetary disk. Our proposed mechanism for Planetesimal disk growth does not require any special conditions to operate. Consequently, we expect that high mass Planetesimal disks form naturally in nearly all systems. The extent of this growth is controlled by the total mass in pebbles that drifts through the inner disk. Anything that reduces the rate or duration of pebble delivery will correspondingly reduce the final mass of the Planetesimal disk. Therefore, we expect that low mass stars (with less massive protoplanetary disks), low metallicity stars and stars with giant planets should all grow less massive Planetesimal disks. The evolution of Planetesimal disks into planetary systems remains a mystery. However, we argue that late stage planet formation models should begin with a massive disk. This reinforces the idea that massive and compact planetary systems could form in situ but does not exclude the possibility that significant migration occurs post-planet formation.
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building massive compact Planetesimal disks from the accretion of pebbles
The Astrophysical Journal, 2015Co-Authors: John Moriarty, Debra A. FischerAbstract:We present a model in which Planetesimal disks are built from the combination of Planetesimal formation and the accretion of radially drifting pebbles onto existing Planetesimals. In this model, the rate of accretion of pebbles onto Planetesimals quickly outpaces the rate of direct Planetesimal formation in the inner disk. This allows for the formation of a high-mass inner disk without the need for enhanced Planetesimal formation or a massive protoplanetary disk. Our proposed mechanism for Planetesimal disk growth does not require any special conditions to operate. Consequently, we expect high-mass Planetesimal disks to form naturally in nearly all systems. The extent of this growth is controlled by the total mass in pebbles that drifts through the inner disk. Anything that reduces the rate or duration of pebble delivery will correspondingly reduce the final mass of the Planetesimal disk. Therefore, we expect low-mass stars (with less massive protoplanetary disks), low-metallicity stars, and stars with giant planets to grow less massive Planetesimal disks. The evolution of Planetesimal disks into planetary systems remains a mystery. However, we argue that late stage planet formation models should begin with a massive disk. This reinforces the idea that massive and compact planetary systems could form in situ, but does not exclude the possibility that significant migration occurs post-planet formation.
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chemistry in an evolving protoplanetary disk effects on terrestrial planet composition
arXiv: Earth and Planetary Astrophysics, 2014Co-Authors: John Moriarty, Nikku Madhusudhan, Debra A. FischerAbstract:The composition of planets is largely determined by the chemical and dynamical evolution of the disk during Planetesimal formation and growth. To predict the diversity of exoplanet compositions, previous works modeled Planetesimal composition as the equilibrium chemical composition of a proto- planetary disk at a single time. However, Planetesimals form over an extended period of time, during which, elements sequentially condense out of the gas as the disk cools and are accreted onto planetesi- mals. To account for the evolution of the disk during Planetesimal formation, we couple models of disk chemistry and dynamics with a prescription for Planetesimal formation. We then follow the growth of these Planetesimals into terrestrial planets with N-body simulations of late stage planet formation to evaluate the effect of sequential condensation on the bulk composition of planets. We find that our model produces results similar to those of earlier models for disks with C/O ratios close to the solar value (0.54). However, in disks with C/O ratios greater than 0.8, carbon rich Planetesimals form throughout a much larger radial range of the disk. Furthermore, our model produces carbon rich Planetesimals in disks with C/O ratios as low as ~0.65, which is not possible in the static equilibrium chemistry case. These results suggest that (1) there may be a large population of short period carbon rich planets around moderately carbon enhanced stars (0.65 0.8).
Hagai B. Perets - One of the best experts on this subject based on the ideXlab platform.
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Application of gas dynamical friction for Planetesimals: I. Evolution of single Planetesimals
The Astrophysical Journal, 2015Co-Authors: Evgeni Grishin, Hagai B. PeretsAbstract:The growth of small Planetesimals into large planetary embryos occurs much before the dispersal of the gas from the protoplanetary disk. The Planetesimal - gaseous-disk interactions give rise to migration and orbital evolution of the Planetesimals/planets. Small Planetesimals are dominated by aerodynamic gas drag. Large protoplanets, $m\sim0.1M_{\oplus}$, are dominated by type I migration \emph{differential} torque. There is an additional mass range, $m\sim10^{21}-10^{25}g$ of \emph{intermediate mass} Planetesimals (IMPs), where gravitational interactions with the disk dominate over aerodynamic gas drag, but for which such interactions were typically neglected. Here we model these interactions using the \emph{gas dynamical friction} (GDF) approach, previously used to study the disk-planet interactions at the planetary mass range. We find the critical size where GDF dominates over gas drag, and then study the implications of GDF on single IMPs. We find that Planetesimals with small inclinations rapidly become co-planar. Eccentric orbits circularize within a few Myrs, provided the the Planetesimal mass is large, $m\gtrsim10^{23}g$ and that the initial eccentricity is low, $e\lesssim0.1$. Planetesimals of higher masses, $m\sim10^{24}-10^{25}g$ inspiral on a time-scale of a few Myrs, leading to \emph{an embryonic migration} to the inner disk. This can lead to an over-abundance of rocky material (in the form of IMPs) in the inner protoplanetary disk ($
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BINARY PlanetesimalS AND THEIR ROLE IN PLANET FORMATION
The Astrophysical Journal, 2010Co-Authors: Hagai B. PeretsAbstract:One of the main evolutionary stages of planet formation is the dynamical evolution of Planetesimal disks. These disks are thought to evolve through gravitational encounters and physical collisions between single Planetesimals. In recent years, many binary Planetesimals (BPs) have been observed in the solar system, indicating that the binarity of Planetesimals is high. However, current studies of Planetesimal disk formation and evolution do not account for the role of binaries. Here, we point out that gravitational encounters of BPs can have an important role in the evolution of Planetesimal disks. BPs catalyze close encounters between Planetesimals and can strongly enhance their collision rate. Binaries may also serve as an additional heating source of the Planetesimal disk, through the exchange of the binaries gravitational potential energy into the kinetic energy of Planetesimals in the disk.
