Understanding planet formation using microgravity experiments

Wurm, Gerhard; Teiser, Jens

doi:10.1038/s42254-021-00312-7

Cited by 28 publications

(8 citation statements)

References 256 publications

(313 reference statements)

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“…Quite generally, there is little doubt that aggregation starts out fractal and highly porous (Blum & Wurm 2000;Wurm & Teiser 2021). As we find decreasing coupling times here, collision velocities are slower.…”

Section: Discussionmentioning

confidence: 99%

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Drag forces on porous aggregates in protoplanetary disks

Schneider

Wurm

2021

A&A

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Context. In protoplanetary disks, particle–gas interactions are a key part of the early stages of pre-planetary evolution. As dust particles grow into porous aggregates, treating drag forces of aggregates in the same way as those of monolithic compact spheres has always been an approximation. Aims. The substructures and building blocks of aggregates may respond differently to different drag regimes than the overall size of the porous body would suggest. The influence of porosity and substructure size on the drag on porous bodies is studied. Methods. We measured centimeter-sized porous aggregates with volume filling factors as low as ~10−4 for the first time in low-pressure wind tunnel experiments. Various substructures of different sizes down to micrometer (μm) resolution are tested. Knudsen numbers for the centimeter-sized superstructure are between 0.005 and 0.1 and Reynolds numbers are between 5 and 130. Results. We find that bodies are subject to increasingly large drag forces with increasing porosity, significantly larger than previously thought. In the parameter range measured, drag can increase by a factor of 23, and extrapolation suggests even larger values. We give an empirically determined model for an adjusted drag force. Conclusions. Our findings imply that the coupling of highly porous bodies in protoplanetary disks is significantly stronger than assumed in previous works. This decreases collision velocities and radial drift speeds and might allow porous bodies to grow larger under certain conditions before they become compacted.

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Section: Discussionmentioning

confidence: 99%

“…For the first stage of planet formation, it is widely accepted that micron or sub-micron dust grains grow via collisional growth to millimeter-or centimeter-sized aggregates (Blum & Wurm 2008;Wurm & Teiser 2021). However, these aggregates are neither spherical nor compact.…”

Section: Introductionmentioning

confidence: 99%

Drag forces on porous aggregates in protoplanetary disks

Schneider

Wurm

2021

A&A

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“…Regarding grains of this size, there exist a couple of studies on ejection related to planet formation. In these studies, dust aggregates and their collisions are a fundamental process (Wurm & Teiser 2021).…”

Section: Introductionmentioning

confidence: 99%

Releasing Atmospheric Martian Dust in Sand Grain Impacts

et al. 2022

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Emission of dust up to a few microns in size by impacts of sand grains during saltation is thought to be one source of dust within the Martian atmosphere. To study this dust fraction, we carried out laboratory impact experiments. Small numbers of particles of about 200 μm in diameter impacted a simulated Martian soil (bimodal Mars Global Simulant). Impacts occurred at angles of ∼18° in vacuum with an impact speed of ∼1 m s−1. Ejected dust was captured on adjacent microscope slides and the emitted particle size distribution (PSD) was found to be related to the soil PSD. We find that the ejection of clay-sized dust gets increasingly harder the smaller these grains are. However, in spite of strong cohesive forces, individual impacts emit dust of 1 μm and less, i.e., dust in the size range that can be suspended in the Martian atmosphere. More generally, the probability of ejecting dust of a given size can be characterized by a power law in the size range between 0.5 and 5 μm (diameter).

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“…This section gives a brief overview of the different technical approaches of experiments regarding early planet formation processes. The first kind of experiments deals with the aggregation of dust particles in the PPD (Blum and Wurm, 2000a;Weidling et al, 2012;Wurm and Teiser, 2021). These experiments are designed either to understand the aggregation of the first solids of the Solar System, or to understand how objects like chondrules aggregated to larger objects.…”

Section: Experimental Approaches To Study Early Solar System Processesmentioning

confidence: 99%

“…These experiments are designed either to understand the aggregation of the first solids of the Solar System, or to understand how objects like chondrules aggregated to larger objects. Most of these experiments have been carried out under microgravity conditions (Blum and Wurm, 2000a,b;Wurm and Teiser, 2021). There are different possibilities to achieve a microgravity environment which have been used for planetary science experiments:…”

Section: Experimental Approaches To Study Early Solar System Processesmentioning

confidence: 99%

Experimental study of early solar system processes aboard the international space station

Koch¹

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The formation of terrestrial planets was a complex process which begun in the very early stage of the Solar System in the protoplanetary disk (PPD). Chondrites are fragments of planet precursors, which have never experienced differentiation and can help to reconstruct the first processes leading to planet formation. The main components of chondrites are chondrules, calcium-aluminum-rich inclusions (CAIs), amoeboid olivine aggregates (AOAs), metals and fine-grained material. Each of these components formed by a complex mechanism involving aggregation and/or melting. Previous research has already provided an overall view of the formation of these objects, however, there are still open questions regarding the aggregation behavior of particles, the heating mechanism(s) and the thermal history of CAIs, AOAs and chondrules. For instance, the involvement of flash-heating events and electrostatics in the aggregation and melting of these objects has been a keen topic of discussion. The aim of this doctoral thesis was to develop and carry out an experiment to study various early Solar System processes under long-term microgravity. In the project with the acronym EXCISS (Experimental Chondrule Formation aboard the ISS), free-floating, 126(23)µm-sized Mg2SiO4 dust particles were exposed to electric fields and electric discharges. The experimental set-up was installed inside a 10x10x15 cm3-sized container and consisted of an arc generation unit connected to the sample chamber, a camera with an optical system, a power supply unit with lithium-ion batteries and the EXCISS mainboard with a Raspberry Pi Zero and mass storage devices. The sample chamber was manufactured from quartz glass and the experiments were filmed. The complete experiment container was subsequently returned to the Goethe University and the samples were analyzed with scanning electron microscopy, electron backscatter diffraction and synchrotron micro-CT. Video analysis has shown that particles, which were agitated by electric discharges, align in chains within the electric field with their longest axis parallel to the electric field lines. Consequently, electric fields could have influenced the inner structure and porosity of particle aggregates in the PPD. The discharge experiments produced fused aggregates and individual melt spherules. The fused aggregates share many morphological characteristics with natural fluffy-type CAIs and some igneous CAIs found in chondrites. Consequently, CAIs could have formed by the aggregation of particles with various degrees of melting. Further, a small amount of melting could have supplied the required stability for such fractal structures to have survived transportation and aggregation to, and subsequent compaction within, developing planetesimals. Some initial particles were completely melted by the arc discharges and formed melt spherules. The newly formed olivines crystallized with a preferred orientation of the [010] axis perpendicular to the surface of the spherule. Similar preferred orientations have been found in natural chondrules. However, the microstructure differs from the results of previous experiments on Earth, which show, for example, crystal settling on one side of the sample because of the influence of gravity. Furthermore, the melt spherules show evidence for an interaction of the melt with the surrounding hot gas. Therefore, microgravity experiments with more advanced experimental parameters bear great potential for future chondrule formation experiments.

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Understanding planet formation using microgravity experiments

Cited by 28 publications

References 256 publications

Drag forces on porous aggregates in protoplanetary disks

Drag forces on porous aggregates in protoplanetary disks

Releasing Atmospheric Martian Dust in Sand Grain Impacts

Experimental study of early solar system processes aboard the international space station

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