NASA NTRS1994
Owen et al. propose that the Ar excess of Venus compared to Earth was caused by impact of a large icy planetesimal from the outer solar system, where temperatures were low enough for Ar to adhere to ice, about 30 K. A body of solar Ar/Si and C/H similar to Pluto and Triton less than 100 km diameter would suffice. However, direct delivery from the Uranus-Neptune zone to Venus would result in a very high approach velocity, causing erosion rather than accretion of volatiles. It would also be an extremely improbable event. Virtually all icy bodies scattered from the Uranus-Neptune zone to the terrestrial zone were strongly perturbed by Jupiter, but even then arrived at Venus (or Earth) at too-high velocities. What is needed is a 'deboost' of bodies scattered inward from Jupiter by Earth and Venus perturbations, prior to impact into Venus. This has low probability, since the influence radii of Venus and Earth for the high velocities are small compared to that of Jupiter for the lower velocities further out. It is desirable that this problem be examined by an integerator that allows for close approaches, such as developed by Levison and Duncan. However, it would be a long and expensive computation compared to explaining short-period comets to accomplish the third 'deboost' phase. But since close encounters dominate in such distant scattering, an Opik algorithm seems the appropriate reconnaissance tool.