![]() developed the first numerical model of impact jetting during blunt-body penetration using the iSALE shock physics code and presented the jet velocity as a function of impact velocity along with the jetted mass. However, they did not investigate the origin of such a high-velocity component, possibly because of the limited spatial and/or temporal resolution of their experiment. They reported that the maximum ejection velocity reached a few times the impact velocity. Note that Eichhorn and Kadono and Fujiwara measured the velocities of ejected materials during impacts of spherical projectiles under various experimental conditions. Although the temperature of jetted vapor in oblique impacts has been investigated under a wide range of experimental conditions, only a few data points have been reported for the jet velocity during blunt-body penetration, despite this being one of the important benchmarks to constructing a jetting model for spherical projectiles during oblique impacts. Assembly of a systematic data set pertaining to the jet-velocity behavior during oblique impacts of spherical projectiles is necessary to investigate the significance of impact jetting in the geologic problems as mentioned above. ![]() Hydrodynamic flows driven during the penetration of a blunt body are very complicated, because they are time dependent and asymmetric. However, a detailed understanding of the jetting occurring during blunt-body penetration, which is essential for planetary applications, has not yet been fully achieved. Jetting during a symmetric collision between two thin plates has been studied extensively. This may contribute to an increase in the rock-to-ice ratio of the Pluto-Charon system. In addition, McKinnon showed that impacts owing to collisions between icy planetesimals cause an escape of water vapor from the system. ![]() Melosh and Sonett pointed out that a large amount of silicate vapor, as produced by impact jetting, may be important during giant impacts through injection of the ejected materials into a stable Earth orbit, facilitated by the silicate vapor's pressure gradient. Based on these intense features, impact jetting has been considered as a viable mechanism to explain the origin of chondrules and impact glasses. There are two important features associated with impact jetting : (1) the jet velocity is greater than the impact velocity and (2) jetted materials suffer the highest degree of shock heating during an impact event. This phenomenon is widely known as “impact jetting”. Hypervelocity material ejection during oblique convergence between two thin plates has been observed in both hypervelocity impact experiments and hydrocode calculations. Based on the extremely high velocity of the jet, we point out that impact jetting might contribute to chemistry near the ground surface of planets/satellites with a thick atmosphere, such as Titan. The particle velocities of ejected materials from a free surface are calculated using the Riemann invariant along the isentropes and the Tillotson equations of state in this study. We also present a new formulation of the jet velocity with the equations of state for realistic materials. ![]() A decaying shock pressure during blunt-body penetration is a possible origin of the discrepancy. We find that the jet velocities measured in this study are much slower than the prediction by the standard theory based on the previous experimental/theoretical results of collisions between two metal plates. The maximum jet velocity was obtained as a function of both impact velocity and the contrast of shock impedance between a projectile and target, enabling us to test theoretical models of impact jetting during oblique impacts of spherical projectiles. The observations were sampled at a frame rate of 100 ns frame −1, which is much shorter than the characteristic time of projectile penetration under our experimental conditions. We present the results of high-speed imaging observations of impact jetting during blunt-body penetration under oblique impacts. A series of hypervelocity impact experiments was conducted in a new laboratory at Planetary Exploration Research Center of Chiba Institute of Technology (Japan).
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