Crater size scaling in the strength-dominated regime for weak porous targets: Implications for the tensile strength of asteroid surfaces
Ryo Sugimura, Masahiko Arakawa, Minami Yasui
Icarus, In Press, Journal Pre-proof, Available online 27 May 2026
“Highlights
- Impact craters were experimentally formed on weak porous targets.
- Crater size dependence on tensile strength was obtained for 2–760 kPa.
- The depth-to-diameter ratio exhibited a strong correlation with tensile strength.
- The surface tensile strength of Ryugu was inferred to be as low as 0.5 Pa.
- The tensile strength of Bennu’s boulders ranged between 2 and 90 kPa.”
“Laboratory impact cratering experiments on weak porous targets were conducted to constrain the cohesion of the uppermost layer of asteroid (162173) Ryugu and to estimate the range of tensile strength of boulders on asteroid (101955) Bennu motivated by recent spacecraft observations of small-body surfaces. Impact experiments were conducted at velocities of 2.5, 4, and 6 km s−1 on targets composed of quartz–gypsum mixtures. The tensile strength of these mixtures ranged from 2 kPa to 760 kPa, and the porosity varied between 35% and 43%. Consequently, the crater morphology exhibited a transition from a pit-type to a bowl-type crater, characterized by a central pit, and subsequently to a dish-type crater reflecting systematic changes in target strength. This transformation was observed as the tensile strength decreased at all impact velocities.
The depth-to-diameter ratios (dcr/Dcr) of the crater were well correlated with the tensile strength Yt as follows: dcr/Dcr = 0.138+0.114 log Yt[kPa]. This indicates that the crater becomes shallower with respect to its diameter as the tensile strength decreases. This empirical equation was applied to estimate the tensile strength of boulders on Bennu using the depth-to-diameter ratios measured for seven large craters on Bennu’s boulders. The tensile strength was determined to range between 2 and 90 kPa, irrespective of the boulder diameter suggesting substantial strength heterogeneity among surface boulders.
The crater size was also well correlated with the tensile strength and the impact velocity, and it decreased with increasing tensile strength and decreasing impact velocity. Therefore, a crater size scaling relationship in the strength-dominated regime was derived based on these results providing quantitative laboratory constraints for weak cohesive materials. By integrating this relationship with the scaling relationship for dry sand in the gravity-dominated regime, a generalized crater size scaling relationship was established. Using this scaling relationship, the crater radius of the SCI crater formed by Hayabusa 2 mission on Ryugu was successfully reproduced with a tensile strength as low as 0.5 Pa. This result indicates that the SCI crater was formed in the transitional regime between the strength-dominated and gravity-dominated regimes, and that the surface tensile strength could be lower than 1 Pa consistent with extremely weak surface cohesion inferred for rubble-pile asteroids.”
