In previous laboratory experiments, we measured the temperature dependence of sticking forces between micrometer grains of chondritic composition. The data showed a decrease in surface energy by a factor ~5 with increasing temperature. Here, we focus on the effect of surface water on grains. Under ambient conditions in the laboratory, multiple water layers are present. At the low pressure of protoplanetary discs and for moderate temperatures, grains likely only hold a monolayer. As dust drifts inwards, even this monolayer eventually evaporates completely in higher temperature regions. To account for this, we measured the tensile strength for the same chondritic material as was prepared and measured under normal laboratory conditions in our previous work, but now introducing two new preparation methods: drying dust cylinders in air (dry samples), and heating dust pressed into cylinders in vacuum (super-dry samples). For all temperatures up to 1000 K, the data of the dry samples are consistent with a simple increase in the sticking force by a factor of ~10 over wet samples. Up to 900 K super-dry samples behave like dry samples. However, the sticking forces then exponentially increase up to another factor ~100 at about 1200 K. The increase in sticking from wet to dry extends a trend that is known for amorphous silicates to multimineral mixtures. The findings for super-dry dust imply that aggregate growth is boosted in a small spatial high-temperature region around 1200 K, which might be a sweet spot for planetesimal formation.
Sticking properties rule the early phases of pebble growth in protoplanetary discs in which grains regularly travel from cold, water-rich regions to the warm inner part. This drift affects composition, grain size, morphology, and water content as grains experience ever higher temperatures. In this study we tempered chondritic dust under vacuum up to 1400 K. Afterwards, we measured the splitting tensile strength of millimetre-sized dust aggregates. The deduced effective surface energy starts out as $γ_e = 0.07\,\rm J/m^2$. This value is dominated by abundant iron-oxides as measured by Mössbauer…
We study a potential genetic relationship of comets C/1846 O1 and C/1973 D1, whose apparent orbital similarity was tested by Kresak (1982) only statistically, using the Southworth-Hawkins (1963) criterion D. Our orbit determination for C/1846 O1 shows its period was ~500 yr, ~30 times shorter than that of C/1973 D1. Formerly unrecognized, this incongruity makes the objects' common origin less likely. Long-term orbit integration suggests that, if related, the two comets would have to have separated far away from the Sun (probably ~700 AU) 21 millennia ago and, unlike C/1973 D1, C/1846 O1 would …
Secular gravitational instability (GI) is one of the promising mechanisms for creating annular substructures and planetesimals in protoplanetary disks. We perform numerical simulations of the secular GI in a radially extended disk with inward drifting dust grains. The results show that, even in the presence of the dust diffusion, the dust rings form via the secular GI while the dust grains are moving inward, and the dust surface density increases by a factor of ten. Once the secular GI develops into a nonlinear regime, the total mass of the resultant rings can be a significant fraction of the …
In the pebble accretion scenario, the pebbles that form planets drift inward from the outer disk regions, carrying water ice with them. At the water ice line, the water ice on the inward drifting pebbles evaporates and is released into the gas phase, resulting in water-rich gas and dry pebbles that move into the inner disk regions. Large planetary cores can block the inward drifting pebbles by forming a pressure bump outside their orbit in the protoplanetary disk. Depending on the relative position of a growing planetary core relative to the water ice line, water-rich pebbles might be blocked …
Observationally inferred crystalline abundance in silicates in comets, which should have been formed in the outer region of a protoplanetary disk, is relatively high (~ 10-60%), although crystalline silicates would be formed by annealing of amorphous precursors in the disk inner region. In order to quantitatively address this puzzle, we have performed Monte Carlo simulation of advection/diffusion of silicate particles in a turbulent disk, in the setting based on pebble accretion model: pebbles consisting of many small amorphous silicates embedded in icy mantle are formed in the disk outer regi…
In dead zones of protoplanetary discs, it is assumed that micrometre-sized particles grow Brownian, sediment to the midplane and drift radially inward. When collisional compaction sets in, the growing aggregates collect slower and therefore dynamically smaller particles. This sedimentation and growth phase of highly porous ice and dust aggregates is simulated with laboratory experiments in which we obtained mm- to cm-sized ice aggregates with a porosity of 90\% as well as cm-sized dust agglomerates with a porosity of 85\%. We modelled the growth process during sedimentation in an analytical ca…
Dust drifting inward in protoplanetary disks is subject to increasing temperatures. In laboratory experiments, we tempered basaltic dust between 873 K and 1273 K and find that the dust grains change in size and composition. These modifications influence the outcome of self-consistent low speed aggregation experiments showing a transition temperature of 1000\,K. Dust tempered at lower temperatures grows to a maximum aggregate size of $2.02 \pm 0.06$ mm, which is $1.49 \pm 0.08$ times the value for dust tempered at higher temperatures. A similar size ratio of $1.75 \pm 0.16$ results for a differ…
Observational data on the dust content of circumstellar disks show that the median dust content in disks around pre-main sequence stars in nearby star forming regions seem to increase from about 1 Myr to about 2 Myr, and then decline with time. This behaviour challenges the models where the small dust grains steadily decline by accumulating into larger bodies and drifting inwards on a short timescale (less than about 1 Myr). In this Letter we explore the possibility to reconcile this discrepancy in the framework of a model where the early formation of planets dynamically stirs the nearby plane…
Context. Circumstellar disks are known to contain a significant mass in dust ranging from micron to centimeter size. Meteorites are evidence that individual grains of those sizes were collected and assembled into planetesimals in the young solar system. Aims. We assess the efficiency of dust collection of a swarm of non-drifting planetesimals {\rev with radii ranging from 1 to $10^3$\,km and beyond. Methods. We calculate the collision probability of dust drifting in the disk due to gas drag by planetesimal accounting for several regimes depending on the size of the planetesimal, dust, and orbi…
In laboratory experiments, we heated chondritic material up to 1400K in a hydrogen atmosphere. Moessbauer spectroscopy and magnetometry reveal that, at high temperatures, metallic iron forms from silicates. The transition temperature is about 1200K after 1 h of tempering, likely decreasing to about 1000K for longer tempering. This implies that in a region of high temperatures within protoplanetary disks, inward drifting solids will generally be a reservoir of metallic iron. Magnetic aggregation of iron-rich matter then occurs within the magnetic field of the disk. However, the Curie temperatur…
The growth of a pebble accreting planetary core is stopped when reaching its \textit{isolation mass} that is due to a pressure maximum emerging at the outer edge of the gap opened in gas. This pressure maximum traps the inward drifting pebbles stopping the accretion of solids onto the core. On the other hand, a large amount of pebbles ($\sim 100M_\oplus$) should flow through the orbit of the core until reaching its isolation mass. The efficiency of pebble accretion increases if the core grows in a dust trap of the protoplanetary disc. Dust traps are observed as ring-like structures by ALMA sug…
In evolved and dusty circumstellar discs, two planets with masses comparable to Jupiter and Saturn that migrate outwards while maintaining an orbital resonance can produce distinctive features in the dust distribution. Dust accumulates at the outer edge of the common gas gap, which behaves as a dust trap, where the local dust concentration is significantly enhanced by the planets outward motion. Concurrently, an expanding cavity forms in the dust distribution inside the planets orbits, because dust does not filter through the common gaseous gap and grain depletion in the region continues via i…
The latest observation of HL Tau by ALMA revealed spectacular concentric dust rings in its circumstellar disk. We attempt to explain the multiple ring structure as a consequence of aggregate sintering. Sintering is known to reduce the sticking efficiency of dust aggregates and occurs at temperatures slightly below the sublimation point of their constituent material. We here present a dust growth model incorporating sintering and use it to simulate global dust evolution due to sintering, coagulation, fragmentation, and radial inward drift in a modeled HL Tau disk. We show that aggregates consis…
The early stages of planet formation are still not well understood. Coagulation models have revealed numerous obstacles to the dust growth, such as the bouncing, fragmentation and radial drift barriers. We study the interplay between dust coagulation and drift in order to determine the conditions in protoplanetary disk that support the formation of planetesimals. We focus on planetesimal formation via sweep-up and investigate whether it can take place in a realistic protoplanetary disk. We have developed a new numerical model that resolves spatial distribution of dust in the radial and vertica…
Recent observations of protoplanetary disks have revealed ring-like structures that can be associated to pressure maxima. Pressure maxima are known to be dust collectors and planet migration traps. Most of planet formation works are based either on the pebble accretion model or on the planetesimal accretion model. However, recent studies proposed the possible formation of Jupiter by the hybrid accretion of pebbles and planetesimals. We aim to study the full process of planet formation consisting of dust evolution, planetesimal formation and planet growth at a pressure maximum in a protoplaneta…
We study the dynamics and growth of dust particles in circumstellar disks of different masses that are prone to gravitational instability during the critical first Myr of their evolution. The dust component is made up of two different components: micron-sized dust and grown dust of evolving size. For the dust component, we considered the dust coagulation, fragmentation, momentum exchange with the gas, and dust self-gravity. We found that the micron-sized dust particles grow rapidly in the circumstellar disk, reaching a few cm in size in the inner 100 au of the disk during less than 100 kyr aft…
We discovered a new growth mode of dust grains to km-sized bodies in protoplanetary disks that evolve by viscous accretion and magnetically driven disk winds (MDWs). We solved an approximate coagulation equation of dust grains with time-evolving disks that consist of both gas and solid components by a one-dimensional model. With the grain growth, all solid particles initially drift inward toward the central star by the gas drag force. However, the radial profile of gas pressure, $P$, is modified by the MDW that disperses the gas in an inside-out manner. Consequently, a local concentration of s…
The GAPS Programme at TNG LXVII. Detection of water and preliminary characterisation of the atmospheres of the two hot Jupiters KELT-8 b and KELT-23 Ab
