Effects of oblique impacts on the impact strength of porous gypsum and glass spheres: Implications for the collisional disruption of planetesimals in thermal evolution

1Minami Yasui,1Masahiko Arakawa,1 Yusaku Yoshida,1Kazuma Matsue,1 Shota Takano
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.113414]
1Graduate School of Science, Kobe University 1-1, Rokkodai-cho, Nada-ku, Kobe, Hyogo 657-8501, Japan
Copyright Elsevier

We conducted oblique impact experiments for porous gypsum spheres and glass spheres simulating primitive and consolidated rocky planetesimals, respectively, and we determined the effects of the impact angle on the impact strength of these rocky planetesimals. The targets were a porous gypsum sphere with a porosity of 50% and a glass sphere without porosity. A spherical polycarbonate projectile impacted the target at 2–7 km s−1 at an impact angle, θ, ranging from 90° (head-on collision) to 10° (grazing collision) by using a two-stage light-gas gun at Kobe University, Japan. The impact strength obtained at a head-on collision was 1330 J kg−1 for the porous gypsum target and 1090 J kg−1 for the glass target, and these values increased markedly with the decrease of the impact angle when the impact angle was smaller than a critical angle, θc; the obtained θc values were 30° for the porous gypsum target and 55° for the glass target. The normalized largest fragment mass (ml/Mt) showed a good correlation with an effective specific energy (Qeff = Qsin2θ); the subsequent empirical equation was ml/Mt=102.02Qeff0.76 for the porous gypsum target and ml/Mt=104.66Qeff1.68 at ml/Mt <0.75 and ml/Mt=100.12Qeff0.08 at ml/Mt >0.75 for the glass target. Based on our experimental results, we successfully introduce the effects of an oblique impact on the degree of disruption for primitive and consolidated rocky planetesimals. Our findings demonstrate that in a strength-dominated regime, the catastrophic disruption can occur over a wide range of impact angles (30°–90°) irrespective of the target materials, when the specific energy at the collision is about four times larger than the impact strength.


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