Survivability of copper projectiles during hypervelocity impacts in porous ice: A laboratory investigation of the survivability of projectiles impacting comets or other bodies

Abstract

a b s t r a c tDuring hypervelocity impact (>a few km s À1 ) the resulting cratering and/or disruption of the target body often outweighs interest on the outcome of the projectile material, with the majority of projectiles assumed to be vaporised. However, on Earth, fragments, often metallic, have been recovered from impact sites, meaning that metallic projectile fragments may survive a hypervelocity impact and still exist within the wall, floor and/or ejecta of the impact crater post-impact. The discovery of the remnant impactor composition within the craters of asteroids, planets and comets could provide further information regarding the impact history of a body. Accordingly, we study in the laboratory the survivability of 1 and 2 mm diameter copper projectiles fired onto ice at speeds between 1.00 and 7.05 km s À1 . The projectile was recovered intact at speeds up to 1.50 km s À1 , with no ductile deformation, but some surface pitting was observed. At 2.39 km s À1 , the projectile showed increasing ductile deformation and broke into two parts. Above velocities of 2.60 km s À1 increasing numbers of projectile fragments were identified post impact, with the mean size of the fragments decreasing with increasing impact velocity. The decrease in size also corresponds with an increase in the number of projectile fragments recovered, as with increasing shock pressure the projectile material is more intensely disrupted, producing smaller and more numerous fragments. The damage to the projectile is divided into four classes with increasing speed and shock pressure: (1) minimal damage, (2) ductile deformation, start of break up, (3) increasing fragmentation, and (4) complete fragmentation. The implications of such behaviour is considered for specific examples of impacts of metallic impactors onto Solar System bodies, including LCROSS impacting the Moon, iron meteorites onto Mars and NASA's ''Deep Impact" mission where a spacecraft impacted a comet.

Interstellar Objects in the Solar System: 1. Isotropic Kinematics from the Gaia Early Data Release 3

“…Biomarkers can survive at least at the lower part of the hypervelocity range (Burchell et al 2014), and it seems likely that a immediate (or prompt) cloud of very hot plasma would eject cooler, chemically intact, material that could be sampled in a fast flyby. Some material can survive even very fast impacts (McDermott et al 2016), and it seems possible that even hypervelocity ISOs could serve as a means for lithopanspermia (Belbruno et al 2012). At even higher velocities, the impact energy / atom controls the prompt response to the impact.…”

Survival of the impactor during hypervelocity collisions – II. An analogue for high-porosity targets

“…Another explanation is that the peridot projectiles have a fragmentation behaviour different from that of more ductile (i.e. metal) projectiles (Hernandez, Murr & Anchondo 2006;Kenkmann et al 2013;McDermott et al 2016).…”

Experimental Simulations of Hypervelocity Impact Penetration of Asteroids Into the Terrestrial Ocean and Benthic Cratering

“…This is consistent with the flattening of stainless steel in the 5‐km/s impact by shock‐induced deformation and fragmentation (so‐called pancaking) that leads to the increases in C d and S . The flattening of copper projectiles by shock‐induced deformation and fragmentation was also observed in the peak shock pressure from 10 to 60 GPa (McDermott et al., 2016).…”