Giant Impact Induced Atmospheric Blow-off

Previous calculations indicate that the Earth suffered impacts from objects up to Mars size. Such a giant impact may have produced a temporary ejecta-based ring that accreted to form the Moon. To simulate the surface waves from such events we approximated the cratering source as a buried pressurized sphere. For a 10 J impactor we calculated the resulting surface wave using the mode summation method of Sato et al. [1]. For such an impact, the solid Earth free-surface velocity above, and antipodal to, the source achieves 2.6 and 1.9 km/s. Such large ground motions pump the atmosphere and result in upward particle motions which cause the atmosphere to be accelerated to excess of the escape velocity (11.2 km/s) at high altitudes. For a 1.3 x 10 J Moon-forming impact we calculate that ~50% of the Earth’s atmosphere is accelerated to escape.