Hydrocode modeling of oblique impacts: The fate of the projectile

Details Hydrocode modeling of oblique impacts: The fate of the projectile Hydrocode modeling of oblique impacts: The fate of the projectile

Jan 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000m%26ps...35..117p&link_type=abstract

Meteoritics & Planetary Science, vol. 35, no. 1, pp. 117-130 (2000).

Computer Science

58

Scientific paper

All impacts are oblique to some degree. Only rarely do projectiles strike a planetary surface (near) vertically. The effects of an oblique impact event on the target are well known, producing craters that appear circular even for low impact angles (greater than 15( with respect to the surface). However, we still have much to learn about the fate of the projectile, especially in oblique impact events. This work investigates the effect of angle of impact on the projectile. Sandia's three-dimensional hydrocode CTH was used for a series of high-resolution simulations (50 cells per projectile radius) with varying angle of impact. Simulations were carried out for impacts at 90(, 60(, 45(, 30(, and 15( from the horizontal, while keeping projectile size (5 km in radius), type (dunite), and impact velocity (20 km/s) constant. The 3D hydrocode simulations presented here show that in oblique impacts the distribution of shock pressure inside the projectile (and in the target as well) is highly complex, possessing only bilateral symmetry, even for a spherical projectile. Available experimental data suggest that only the vertical component of the impact velocity plays a role in an impact. If this were correct, simple theoretical considerations indicate that shock pressure, temperature, and energy would depend on sin2(, where ( is the angle of impact (measured from the horizontal). However, our numerical simulations show that the mean shock pressure in the projectile is better fit by a sin( dependence, while shock temperature and energy depend on sin3/2(. This demonstrates that in impact events the shock wave is the result of complex processes that cannot be described by simple empirical rules. The mass of shock melt or vapor in the projectile decreases drastically for low impact angles, as a result of the weakening of the shock for decreasing impact angles. In particular, for asteroidal impacts the amount of projectile vaporized is always limited to a small fraction of the projectile mass. In cometary impacts, however, most of the projectile is vaporized even at low impact angles. In the oblique impact simulations a large fraction of the projectile material retains a net downrange motion. In agreement with experimental work, the simulations show that for low impact angles (30( and 15(), a downrange focusing of projectile material occurs, and a significant amount of it travels at velocities larger than the escape velocity of Earth.

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