Shape-changing collisions on comet 67P. We use SPH to simulate impacts of a R_p = 100 m projectile on the smaller of the two lobes of comet 67P. The minimal specific energy required to cause a significant change of the comet’s shape by such impacts, Q_reshape, is estimated for different impact geometries and rotation axis. The material strength is the same in all cases shown here (Y_T = 10 Pa). The effect of the material’s sound speed is investigated as well (top row; in this case, a bulk modulus of A = 2.67 × 10⁴ Pa instead of the nominal A = 2.67 × 10⁶ Pa is used). Plotted is a surface of constant density which represents the surface of the comet; shown in red are regions on the surface with materials whose prescribed tensile strength was exceeded. As a rough average, the minimal specific energy required to cause a significant shape change is estimated as Q_reshape ~ 0.2 ± 0.1 J/kg, as indicated by the horizontal yellow line.