Sublimation of ice-dust mixtures in cooled vacuum environments to reproduce cometary morphologies

Abstract

Aims. The morphology of cometary surfaces can provide important information to constrain the composition and evolution of comets. In this work, we investigate the sublimation behavior of comet analog materials and how the sample composition affects the evolution of morphological features in laboratory experiments. In our experiments, we used dust ice mixtures as analog material to form observed cometary morphologies. Methods. We used ice-dust mixtures in different mixing ratios as cometary analog material. In order to obtain realistic results, we scaled the expected cohesive and gravitational forces on comets to laboratory conditions. The samples were placed in a vacuum sublimation chamber and permanently cooled down to temperatures below 150 K to simulate the space environment. In the experiment, the samples were insolated with a light source from two different directions and alterations on the surface were recorded with a camera. Results. We find that the morphology of sublimation residues of ice-dust mixtures is strongly dependent on the ice-dust ratio as well as the insolation direction. High amounts of ice cause constant surface alteration and lead to exotic morphologies. Low amounts cause fewer and more episodic surface changes during its sublimation. Collapse events resulting in irregular and very rough surfaces occur during horizontal insolation.

Sublimation of organic-rich comet analog materials and their relevance in fracture formation

“…As in previous sublimation experiments (Haack et al 2021), polydisperse fly ash spheres, with an average radius of about 2.4 µm and a density of 2.25 g cm −3 , were used as a refractory dust analog. This material is a compromise between physical and chemical accuracy of dust on a comet.…”

“…This material is a compromise between physical and chemical accuracy of dust on a comet. Fly ash corresponds to the mineralic composition of plagioclase (Haack et al 2021) and is therefore more representative of a mineralic component of a comet compared to particles of pure SiO 2 . Due to their spherical shape, mutual particle interlocking is prevented.…”

“…Most of these experiments were not aimed at reproducing cometary morphologies and were performed with volatile contents of >90 vol%, which are atypical for comets. To produce more realistic morphologies in the laboratory, Haack et al (2021) performed sublimation experiments with more representative dust-ice ratios. They used fly ash (a by-product of industrial coal combustion) as the mineralic dust component and water ice particles as the volatile.…”

“…We decided to expand on previous experiments with refractory fly ash and volatile water ice (Haack et al 2020(Haack et al , 2021 and added organic components as analog materials to the mixtures. The organic components consisted of sodium acetate and glycine in equal parts per mass, which are confirmed on 67P and are nonvolatile materials under our experimental conditions.…”

“…The organic components consisted of sodium acetate and glycine in equal parts per mass, which are confirmed on 67P and are nonvolatile materials under our experimental conditions. Based on the findings of the Rosetta satellite mission and laboratory measurements, we prepared sample mixtures of volatile and nonvolatile materials in different ratios as plausible on a comet (Choukroun et al 2020;Haack et al 2021). For this, we took advantage of the low tensile strength of granular matter composed of spherical particles at temperatures below 150 K (Gundlach et al 2018b;Haack et al 2020).…”