Catastrophic disruption of layered ice-silicate bodies

Large icy Kuiper Belt Objects (KBOs) such as Pluto have observed densities on the order of 1.8 - 2.0 g cm⁻³. This indicates that they are made up of some combination of ice and silicate material; their size further implies that they will possess a differentiated structure with ice dominating towards the surface and silicate material dominating towards the core. A series of impact experiments using the University of Kent’s light gas gun have been carried out in order to determine the impact strength of spherical layered ice-silicate targets that reflect the suspected structure of these bodies. Impacts are also carried out on unlayered ice-silicate targets and pure ice targets for the purposes of comparison. Impact velocities ranged from 1 to 7 km s⁻¹ using a range of projectile sizes and materials including stainless steel, titanium, aluminium and copper. Data from previous work undertaken at the University of Kent is incorporated in order to provide a more complete picture of target behaviour.

Basic spherical ice-silicate targets with diameters of 40mm yield critical energy densities (Q*) of 270 (+2/-26) J kg⁻¹ for 0.8mm stainless steel projectile impacts and 309 (+55/4) J kg⁻¹ for 1mm titanium projectile impacts. This makes them much stronger than large spherical pure ice targets (diameter 0.4 - 1 m) and pure ice cylinders which have critical energy densities of 5.7 (+1.6/-1.2) J kg⁻¹ and 8.1 (+4/- 2.7) J kg⁻¹ respectively when impacted with 1mm copper projectiles. 40mm diameter spherical pure ice targets have a higher energy density of 45 ± 3 J kg'1 when impacted with 1mm aluminium projectiles, indicating some Q* dependence on target size and projectile size which is borne out by other data sets. Size distribution and energy density plots indicate that targets also exhibit different behaviour when impacted at very high energy densities compared to the behaviour displayed at energy densities around the critical energy density. The addition of an ice layer has little to no effect up to a thickness of five times the projectile diameter, after which target strength is increased dramatically to a Q* of 912 (+20/-18) J kg⁻¹ for impacts by 1mm titanium projectiles. However this may not be an accurate reflection of the true strength of large KBOs due to the still-basic nature of the layered targets.