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

Aims. The morphology of cometary nuclei is the result of an ongoing evolution and can provide valuable information to constrain the composition of comets. In our laboratory experiments we investigated the morphological evolution of comet analog materials, which consist of volatile, dust, and organic components. The laboratory results are aimed to help understand the evolution of cometary surfaces. Methods. We used spherical particles of fly ash and mixtures of ice, glycine, and sodium acetate as analog materials in different mass ratios to reproduce observed cometary morphologies. The cohesive and gravitational properties in the laboratory are scaled to cometary conditions to draw meaningful conclusions from the experimental results. The samples were placed in a vacuum sublimation chamber, cooled down to below 150 K, and were insolated with an external light source. To analyze the morphology of the samples, a camera was used to monitor the alterations of the surface. Results. Organic components in volatile-rich samples can have a distinct adhesive effect after the volatiles sublimate. During the sublimation process the sample volume decreases and fractures form on the sample surface. Due to the stability of the remaining volatile-depleted material, significant cliff collapses or ejected particles were not observed in the laboratory.