Catastrophic disruption by hypervelocity impact of multi-layered spherical ice targets

Abstract

The catastrophic disruption of tri-layered spherical icy bodies is reported. The bodies are 19 cm in total diameter, with a central core, an intermediate water layer and an icy surface (each layer respectively approximately 25, 55 and 20% of the total radius). Their response to high-speed impact is investigated at laboratory scales by firing 1.5 mm diameter glass spheres at the targets at speeds in the range 0.9 – 3.2 km s−1 and an ice layer thickness normalised to projectile diameter of typically 20 – 30. The energy density to just break apart such a body (defined as an event where the mass of the largest fragment post-impact is ½ the original target mass) is (3.1±0.1) J kg−1. This is significantly less than that found for similar sized solid ice spheres (18 ± 0.7) J kg−1, water filled ice spheres (16.25 ± 1.35) J kg−1 or hollow ice spheres (25.5 ± 0.5) J kg−1 indicating that the presence of a solid layer beneath an internal ocean, can influence disruption, effectively weakening the body.