Experimental results from CoPhyLab: Influence of Low-Temperature Sintering on the Tensile Strength of Cometary Ice Analogues determined by BDT

Understanding the formation and activity of comets is key to constraining the conditions of the early solar system. As a comet approaches the Sun, its surface water-ice undergoes sintering, forming interparticle necks that significantly alter the ice’s physical properties, including its tensile strength. Gundlach et al. (2018) showed that sintering can proceed at temperatures as low as ~160 K. In this work, we systematically investigate how sintering temperature and duration affect the tensile strength of cometary ice analogues and examine the samples under a low-temperature scanning electron microscope (SEM).

Following the methodology of Kreuzig et al. (2024), we produce granular ice disks at 77 K in a newly designed sample holder. These disks are transferred into a liquid-nitrogen-cooled vacuum chamber, where they are heated from 77 K to a target temperature between 160 K and 200 K, held for variable time intervals on the order of hours, and then cooled back to 77 K to preserve the sintered microstructure. Tensile strength is measured in situ at 77 K using the Brazilian Disk Test (BDT), implemented on a custom apparatus adapted by the author from the CoPhyLab cone-penetration setup (Figure 1).

To resolve the microstructural evolution, sintered samples are examined under a low-temperature SEM, quantifying neck sizes as functions of sintering temperature and time (Figure 2). The resulting dataset will clarify the relationship between sintering parameters and tensile strength, thereby improving models of comet surface mechanics.

Figure 1. Photomontage of the planned Brazilian Disk Test (BDT) setup, analogue to the setup used by Kreuzig et al. (2024). A motor drives a stainless-steel blade, mounted to a precision load cell, downward onto the ice-disk sample seated on the sample table. The load cell continuously records the applied force and registers the peak load at sample failure. Blade displacement is tracked by a camera imaging a small reference tab against an LED backlight strip.

 

Figure 2. SEM picture of granular ice. The ice was kept at 77K at all times, no sintering is expected here and not visible.