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Formation of planetesimals - constraints from cometary dust activity

Presentation #408.07 in the session Comets: Nucleus (Oral Presentation)

Published onOct 23, 2023
Formation of planetesimals - constraints from cometary dust activity

Comets are considered to be among the most primordial bodies in the solar system, but what can they really tell us about their formation? In our earlier work, we showed that mass density, homogeneity, mechanical strength and the dominant particle size of comet 67P are in agreement with a formation via a gentle gravitational collapse of a cloud of dust pebbles, mm- to cm-sized agglomerates of (sub-)µm-sized grains [1]. However, using a thermophysical model of a pebble pile, we failed to model the dust-activity pattern observed for comet 67P along its orbit [2]. In [2], we followed the general assumption that a dust particle is emitted whenever the gas pressure below it exceeds its binding strength, expressed by the tensile strength. New laboratory experiments within the Comet Physics Laboratory (CoPhyLab) project [3] have now shown that this assumption is not valid. In a well-controlled laboratory experiment, we observed continuous dust emission in a sample with a tensile strength of ~1,000 Pa, although the sublimation pressure of the low-temperature water ice never exceeded ~0.2 Pa. Observations of the active sample inside the CoPhyLab thermal-vacuum chamber showed that the dust-emitting surface is highly dynamic and that sintering and evaporation of the water ice go hand-in-hand. Thus, we need a new microphysical description of the processes occuring in the ice-evaporation zone in the near-surface regions of cometary nuclei. We will present the conditions, observations and interpretations of the CoPhyLab experiments and will present new ideas of how cometary dust activity can finally be understood.

References: [1] Blum et al. 2017, MNRAS 469, S755; [2] Bischoff et al., MNRAS (accepted); [3] Kreuzig et al. 2021, Review of Scientific Instruments 92, 115102.

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