Tracing Thermal Creep Through Granular Media

Steinpilz, Tobias; Teiser, Jens; Koester, Marc; Schywek, Mathias; Wurm, Gerhard

doi:10.1007/s12217-017-9550-0

Cited by 9 publications

(9 citation statements)

References 15 publications

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“…If the experiment is placed in a vacuum chamber with low ambient pressure, gas flows from above the aggregates through the pores of the aggregates toward their bottom. This is called thermal creep and requires the mean free path of the gas molecules to be comparable to the pore size (Koester et al 2017;Schywek et al 2017;Steinpilz et al 2017). Therefore, if the pressure is reduced to around 10 mbar, thermal creep leads to an overpres-sure below the aggregates that then lift off and hover over the surface.…”

Section: Methodsmentioning

confidence: 99%

Seeding the Formation of Mercurys: An Iron-sensitive Bouncing Barrier in Disk Magnetic Fields

Kruss

Wurm

2018

ApJ

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The inner part of protoplanetary disks can be threaded by strong magnetic fields. In laboratory levitation experiments, we study how magnetic fields up to 7 mT influence the aggregation of dust by observing the self-consistent collisional evolution of particle ensembles. As dust samples we use mixtures of iron and quartz in different ratios. Without magnetic fields, particles in all samples grow into a bouncing barrier. These aggregates reversibly form larger clusters in the presence of magnetic fields. The size of these clusters depends on the strength of the magnetic field and the ratio between iron and quartz. The clustering increases the size of the largest entities by a factor of a few. If planetesimal formation is sensitive to the size of the largest aggregates, e.g. relying on streaming instabilities, then planetesimals will preferentially grow iron-rich in the inner region of protoplanetary disks. This might explain the iron gradient in the solar system and the formation of dense Mercury-like planets.

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Section: Methodsmentioning

confidence: 99%

Seeding the Formation of Mercurys: An Iron-sensitive Bouncing Barrier in Disk Magnetic Fields

Kruss

Wurm

2018

ApJ

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“…This kind of g-jitter correction is usually done by evaluating parabolic flight experiments (Steinpilz et al 2017;Kraemer et al 2019). For ambient pressures p > 10 −2 mbar the acceleration due to the gas drag is larger than the residual acceleration in z-direction due to the g-jitter (see Fig.…”

Section: Trajectory Analysis and Wind Profilementioning

confidence: 99%

Planetesimals in rarefied gas: wind erosion in slip flow

Demirci

Schneider

Steinpilz

et al. 2020

Monthly Notices of the Royal Astronomical Society

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A planetesimal moves through the gas of its protoplanetary disc where it experiences a head wind. Though the ambient pressure is low, this wind can erode and ultimately destroy the planetesimal if the flow is strong enough. For the first time, we observe wind erosion in ground based and microgravity experiments at pressures relevant in protoplanetary discs, i.e. down to 10 −1 mbar. We find that the required shear stress for erosion depends on the Knudsen number related to the grains at the surface. The critical shear stress to initiate erosion increases as particles become comparable to or larger than the mean free path of the gas molecules. This makes pebble pile planetesimals more stable at lower pressure. However, it does not save them as the experiments also show that the critical shear stress to initiate erosion is very low for sub-millimetre sized grains.

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“…In a low-pressure environment (here, p ≈ 500 Pa) capillaries on the order of the mean free path of the gas molecules and heated on one end efficiently pump gas from the cold to the warm side (Knudsen 1909;Muntz et al 2002, thermal creep). A porous dust aggregate acts like a collection of capillaries (de Beule et al 2015;Koester et al 2017;Steinpilz et al 2017). Therefore, if dust aggregates are placed on a hot surface at low ambient pressure, gas flows from the cold top through the aggregate toward its bottom.…”

Section: Growth Experimentsmentioning

confidence: 99%

Is There a Temperature Limit in Planet Formation at 1000 K?

Demirci¹,

Teiser²,

Steinpilz³

et al. 2017

ApJ

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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 ± 0.06 mm, which is 1.49 ± 0.08 times the value for dust tempered at higher temperatures. A similar size ratio of 1.75 ± 0.16 results for a different set of collision velocities. This transition temperature is in agreement with orbit temperatures deduced for observed extrasolar planets. Most terrestrial planets are observed at positions equivalent to less than 1000 K. Dust aggregation on the millimeter-scale at elevated temperatures might therefore be a key factor for terrestrial planet formation.

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Tracing Thermal Creep Through Granular Media

Cited by 9 publications

References 15 publications

Seeding the Formation of Mercurys: An Iron-sensitive Bouncing Barrier in Disk Magnetic Fields

Seeding the Formation of Mercurys: An Iron-sensitive Bouncing Barrier in Disk Magnetic Fields

Planetesimals in rarefied gas: wind erosion in slip flow

Is There a Temperature Limit in Planet Formation at 1000 K?

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