Giant impact-induced blow-off of primordial atmosphere

Abstract

The surface motion from a large impact upon an attenuation-free fluid sphere was studied and numerically simulated. An analytic solution for the free-surface velocity shows that close to the source, the acoustic wave due to the free-surface interaction (a "quasi-surface wave") is not separable from the direct wave. At >90°, the quasi-surface wave separates and has a larger amplitude than the direct body wave. Near the antipode the quasi-surface wave amplitude is much larger than the direct body wave and is comparable to the direct wave amplitude immediately near the source at 0°. The resulting solution covers both the wave interference range as defined in the asymptotic theory of near-surface wave propagation developed by Russian physicist V.S. Buldyrev reported in 1968, as well as in the geometric ray range. The geometric range theory was described in several papers in terms of multi-geometry reflection by R. Burridge, H. Jeffreys, and E.R. Lapwood in England in 1957 through 1963. For a large surface excitation (e.g., giant ∼10^(27) J impact) a portion of the atmosphere above a plane tangent to Earth at the impact point is launched to velocities greater than the escape velocity. The resulting antipodal free-surface velocity achieved is ∼1.9 km/s, which is sufficient to launch a comparable fraction of the atmosphere to escape.

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