Impact cratering on Venus: Physical and mechanical models

Abstract

Results are presented on laboratory, theoretical and numerical simulations of various phenomena related to impact cratering processes specific to the Venusian environment. Such processes are influenced mainly by two factors: the high atmospheric density and the high surface temperature. Model results are presented for the influence of the atmosphere on high‐velocity meteoroids, the influence of high‐velocity meteoroids on the atmosphere, the influence of atmospheric shock waves on the Venusian surface, and the influence of high crustal temperature on impact melting and melt cooling. New modeling techniques based on the two‐dimensional Free‐Lagrangian method have been employed and show that an icy body of 1‐km radius may reach the bottom of the Venusian atmosphere in a partially dispersed state and form an impact crater approximately 20 km in diameter. A significant amount of energy is transferred to the Venusian atmosphere during meteoroid transit, and the gas dynamic flow will be similar to a strong explosion. Modeling shows that a significant wake of low density will form behind the meteoroid and have an important influence on crater formation and ejecta distribution. According to our estimates, the boundary of the flow of dense gas may correspond to the region of hummocky ejecta deposition observed for Venusian impact craters. The collapse of the gas‐rock debris column on the boundary between the low‐ and high‐density regions may result in a turbiditelike flow outside the hummocky ejecta area. We carried out preliminary laboratory simulations of the interaction of meteoroid shock waves with the surface. Considerable surface disruption is possible, even under the trajectory of an oblique impact. The possibility of “back venting” caused by shock wave pressuring and depressuring in ground pores may provide an explanation for the origin of dark margins. The differences between Venus and Earth for impact melting and melt cooling were examined. Melt generation on Venus should be 20% to 40% greater than on Earth for the same crater diameter. Melt volumes should stay molten about an order of magnitude longer on Venus, leading to substantial melt flows and smooth crater floors.

High-Resolution Calculations of Asteroid Impacts into the Venusian Atmosphere

“…A number of groups have studied the disruption and destruction of bolides striking deep atmospheres (e.g., Passey and Melosh 1980, Basilevsky et al 1987, Ivanov 1988, Ivanov et al 1992, Zahnle 1992, Chyba et al 1993, Chevalier and Sarazin 1994, Boslough et al 1994, Ahrens et al 1994, Takata et al 1994, Field and Ferrara 1995, Svetsov et al 1995, Svetsov 1996, Mac Low 1996, Zahnle 1996, Crawford 1996, 1997, Roulston and Ahrens 1997. The consensus seems to be that impacting bodies of a certain size are disrupted by aerodynamic forces and that mechanical ablation (as opposed to radiative ablation, which is the usual fate of small meteors) plays a major role in the deceleration of the object as a whole (Field and Ferrara 1995, Svetsov et al 1995, Mac Low 1996, Crawford 1996.…”

Natural Transfer of Viable Microbes in Space 1. From Mars to Earth and Earth to Mars

“…However, certain findings could be indicative: for example that an impact can lead to reduction of the gas pressure above it. Ivanov et al (1992) made a combined Russian-American study interpreting measurements by the Russian Venera probes and the American Magellan mission.…”

The Canyon Diablo impact event: Projectile motion through the atmosphere

“…However, this simplification leads to unrealistically thin and wide projectiles and to extremely low final velocities (essentially, deceleration is inversely proportional to the projectile's thickness). Numerical models (Ivanov et al 1992;Ahrens et al 1994;Takata et al 1994;Crawford et al 1995) carried out around the same time that the pancake model was developed (i.e., the time of the collision of comet Shoemaker-Levy 9 with Jupiter) clearly showed that although flattening ("pancaking") is a typical behavior of disrupted projectiles, it is mostly restricted to a flattening factor of 1.7-2.3. Further, widening is arrested by the growth of Kelvin-Helmholtz (K-H) and Rayleigh-Taylor (R-T) instabilities and the resulting projectile fragmentation into smaller pieces.…”