Applicability and limits of simple hydrodynamic scaling for collisions of water-rich bodies in different mass regimes

We investigate the outcome of collisions in very different mass regimes, but an otherwise identical parameter setup, comprising the impact velocity ($v/v_\mathrm{esc}$), impact angle, mass ratio, and initial composition, w.r.t. simple hydrodynamic scaling. The colliding bodies' masses range from $\simeq 10^{16}$ to $10^{24}$ kg, which includes km-sized planetesimals up to planetary-sized objects. Our analysis of the results comprises the time evolution of fragment masses, the fragments' water contents and fragment dynamics, where we start with bodies consisting of basalt and water ice. The usual assumption of hydrodynamic scaling over a wider range of masses is based on material behavior similar to a fluid, or a rubble pile, respectively. All our simulations are carried out once including full solid-body physics, and once for strengthless - but otherwise identical - bodies, to test for the influence of material strength. We find that scale-invariance over a wider range of masses is mostly only a very crude approximation at best, but can be applied to constrained mass ranges if tested carefully. For the chosen scenarios the outcomes of solid-body objects compared to strengthless fluid bodies differ most for our intermediate masses, but are similar for the lowest and highest masses. The most energetic, planet-sized collisions produce considerably faster and more fragments, which is also reflected in high water losses - above 50 percent in a single collision.