When planets smash into each other, they don't splash like liquid—they crunch together like giant, solid rocks.
March 23, 2026
Original Paper
Smoothed Particle Hydrodynamics in pkdgrav3 for Shock Physics Simulations. II. Shear Strength
arXiv · 2603.19764
The Takeaway
Most models of how our solar system formed assume that massive impacts behave like colliding drops of fluid. This study reveals that for objects up to 70% of Earth's mass, the internal strength of the rock actually dictates the outcome, meaning our understanding of the Moon's birth and planetary history may need a major overhaul.
From the abstract
Material strength effects have been recently shown to be significant in giant impacts even at scales of planetary collisions. Despite this, their effects are often neglected in numerical giant impact simulations. We present an implementation of a basic strength model (pressure dependent shear strength) in the massively parallel smoothed particle hydrodynamics code pkdgrav3. The model includes elastic deviatoric stresses, plasticity with pressure-dependent yield strength, and thermal softening, a