Dust evolution and satellitesimal formation in circumplanetary disks

It is believed that satellites of giant planets form in circumplanetary disks. Many of the previous contributions assumed that their formation process proceeds similarly to rocky planet formation, via accretion of the satellite seeds, called satellitesimals. However, the satellitesimal formation itself poses a nontrivial problem as the dust evolution in the circumplanetary disk is heavily impacted by fast radial drift and thus dust growth to satellitesimals is hindered. To address this problem, we connected state-of-the-art hydrodynamical simulations of a circumplanetary disk around a Jupiter-mass planet with dust growth and drift model in a post-processing step. We found that there is an efficient pathway to satellitesimal formation if there is a dust trap forming within the disk. Thanks to the natural existence of an outward gas flow region in the hydrodynamical simulation, a significant dust trap arises at the radial distance of 85~R$_{\rm J}$ from the planet, where the dust-to-gas ratio becomes high enough to trigger streaming instability. The streaming instability leads to the efficient formation of the satellite seeds. Because of the constant infall of material from the circumstellar disk and the very short timescale of dust evolution, the circumplanetary disk acts as a satellitesimal factory, constantly processing the infalling dust to pebbles that gather in the dust trap and undergo the streaming instability.Comment: Accepted for publication in ApJ. Revised version addressing comments from referee and communit

Planet heating prevents inward migration of planetary cores

Planetary systems are born in the disks of gas, dust and rocky fragments that surround newly formed stars. Solid content assembles into ever-larger rocky fragments that eventually become planetary embryos. These then continue their growth by accreting leftover material in the disc. Concurrently, tidal effects in the disc cause a radial drift in the embryo orbits, a process known as migration. Fast inward migration is predicted by theory for embryos smaller than three to five Earth masses. With only inward migration, these embryos can only rarely become giant planets located at Earth's distance from the Sun and beyond, in contrast with observations. Here we report that asymmetries in the temperature rise associated with accreting infalling material produce a force (which gives rise to an effect that we call "heating torque") that counteracts inward migration. This provides a channel for the formation of giant planets and also explains the strong planet-metallicity correlation found between the incidence of giant planets and the heavy-element abundance of the host stars.Comment: 19 pages, 4 figure

First 3-D grid-based gas-dust simulations of circumstellar disks with an embedded planet

Substructures are ubiquitous in high resolution (sub-)millimeter continuum observations of circumstellar disks. They are possibly caused by forming planets embedded in the disk. To investigate the relation between observed substructures and young planets, we perform novel three-dimensional two-fluid (gas+1-mm-dust) hydrodynamic simulations of circumstellar disks with embedded planets (Neptune-, Saturn-, Jupiter-, 5 Jupiter-mass) at different orbital distances from the star (5.2AU, 30AU, 50AU). We turn these simulations into synthetic (sub-)millimeter ALMA images. We find that all but the Neptune-mass planet open annular gaps in both the gas and the dust component of the disk. We find that the temporal evolution of the dust density distribution is distinctly different of the gas'. For example, the planets cause significant vertical stirring of the dust in the circumstellar disk which opposes the vertical settling. This creates a thicker dust disk than disks without a planet. We find that this effect greatly influences the dust masses derived from the synthetic ALMA images. Comparing the dust disk masses in the 3D simulations and the ones derived from the 2D ALMA synthetic images, we find the former to be a factor of a few (up to 10) larger, pointing to that real disks might be significantly more massive than previously thought based on ALMA continuum images using the optically thin assumption and equation. Finally, we analyze the synthetic ALMA images and provide an empirical relationship between the planet mass and the width of the gap in the ALMA images including the effects of the beam size.Comment: 21 pages, 11 figures, accepted for publication in MNRA

Planet formation: The case for large efforts on the computational side

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 planet formation, early evolution, and circumplanetary disks as major fields of interest in computational planet formation. We recommend that modelers relax the approximations of alpha-viscosity and isothermal equations of state, on the grounds that these models use flawed assumptions, even if they give good visual qualitative agreement with observations. We similarly recommend that population synthesis move away from 1D hydrodynamics. The computational resources to reach these goals should be developed during the next decade, through improvements in algorithms and the hardware for hybrid CPU/GPU clusters. Coupled with high angular resolution and great line sensitivity in ground based interferometers, ELTs and JWST, these advances in computational efforts should allow for large strides in the field in the next decade.Comment: White paper submitted to the Astro2020 decadal surve

Planet formation: The case for large efforts on the computational side

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 planet formation, early evolution, and circumplanetary disks as major fields of interest in computational planet formation. We recommend that modelers relax the approximations of alpha-viscosity and isothermal equations of state, on the grounds that these models use flawed assumptions, even if they give good visual qualitative agreement with observations. We similarly recommend that population synthesis move away from 1D hydrodynamics. The computational resources to reach these goals should be developed during the next decade, through improvements in algorithms and the hardware for hybrid CPU/GPU clusters. Coupled with high angular resolution and great line sensitivity in ground based interferometers, ELTs and JWST, these advances in computational efforts should allow for large strides in the field in the next decade

Observability of forming planets and their circumplanetary discs - III. Polarized scattered light in near-infrared

There is growing amount of very high resolution polarized scattered light images of circumstellar discs. Nascent giant planets are surrounded by their own circumplanetary discs that may scatter and polarize both the planetary and stellar light. Here, we investigate whether we could detect circumplanetary discs with the same technique and what can we learn from such detections. Here, we created scattered light mock observations at 1.245 microns (J band) for instruments like SPHERE and GPI, for various planetary masses (0.3, 1.0, 5.0, and 10.0M(Jup)), disc inclinations (90, 60, 30, and 0 deg), and planet position angles (0, 45, and 90 deg). We found that the detection of a circumplanetary disc at 50 au from the star is significantly favoured if the planet is massive (>= 5M(Jup)) and the system is nearly face-on (<= 30 degrees). In these cases, the accretion shock front on the surface of the circumplanetary discs is strong and bright enough to help the visibility of this subdisc. Its detection is hindered by the neighbouring circumstellar disc that also provides a strong polarized flux. However, the comparison between the PI and the Q(phi) maps is a viable tool to pinpoint the presence of the circumplanetary disc within the circumstellar disc, as the two discs are behaving differently on those images.ISSN:0035-8711ISSN:1365-2966ISSN:1365-871

Observability of Forming Planets and their Circumplanetary Disks IV. -- with JWST & ELT

o understand the potential for observing forming planets and their circumplanetary disks (CPDs) with JWST and ELT, we created mock observations from 3D radiative hydrodynamic simulations and radiative transfer post-processing for planets with 10, 5, 1 Jupiter and 1 Saturn masses with orbital separation of 50 and 30 AU in 0∘, 30∘ and 60∘ inclinations. Instrumental effects were then simulated with Mirage for JWST/NIRCam and NIRISS, MIRISim for JWST/MIRI and SimCADO & SimMETIS for ELT/MICADO and METIS. We found that the longer wavelengths (mid-IR and beyond) are the best to detect CPDs. Longer is the wavelength, the smaller mass planet's CPD could be detected. MIRI on JWST and METIS on ELT offers the best possibility on these telescopes. Specifically, below 3 μm, only 10 MJup planets with their CPDs are detectable with NIRCam and MICADO. 5 MJup planets are only detectable if at 30 AU (i.e. closer) orbital separation. Planets above 5 MJup with their CPDs are detectable between 3-5 μm with NIRCam and METIS L/M band, or above 10 μm with MIRI and METIS N band. For ≤ 1 MJup planets > 15 μm are needed, where MIRI uniquely offers imaging capability. We present magnitudes and spectral energy distributions for separate components of the planet+CPD+CSD system, to differentiate the extinction rates of CPDs and CSDs and to provide predictions for observational proposals. Because the CPD turns out to be the main absorber of the planet's emission, especially <10 μm, this makes the detection of forming planets quite challenging