Tensile strength acquired through the memory effect, T(p) − T₀(s), as a function of the compression p experienced by dust-aggregate layers, as measured by Blum et al. (2014). The blue crosses and diamonds represent dust-aggregate radii of (0.66 ± 0.14) mm and (1.29 ± 0.29) mm, respectively. A linear fit to the data (blue dashed line) visualises the memory effect. For comparison, the dotted horizontal lines show the typical CO gas pressure at the ice-dust interface, i.e., the boundary between the covering non-volatile material and the ices, of a cometary nucleus derived for different heliocentric distances by using the model developed by Gundlach et al. (2015). If the gas pressure at the ice-dust interface exceeds the tensile strength of the dust-aggregate layer, gas-driven dust activity is possible.