摘要：Hypervelocity impact would vaporize the impactor and part of planetary surface and create a rock vapor cloud.Results from previous studies suggest that the energetic impact would have a role to blow off and cause a large-scale loss of the planetary atmosphere through expansion of the vapor cloud.Impact also has been considered as a material source.Numerous, repeated impact events during the heavy bombardment period could greatly affect the amount of volatiles and the atmospheric pressure on the planetary surface in either way.To discuss the evolution of the atmospheric pressure by impacts, we carried out hydro-calculations with a two-dimensional hydrodynamic code and investigated the dependence of the loss and supply of the atmosphere on the atmospheric pressure.We integrated both effects by impacts over impactor size distribution and assessed the evolution of the atmospheric pressure on early Mars.Using this approach, we found that the numerous impacts likely increase the atmosphere monotonically or control the atmospheric pressure to some value, rather than causing the monotonic decrease as the previous study suggested.
关键词：Impact erosion ;late heavy bombardment ;Mars atmosphere ;hydrodynamic calculation
