Formation of magnetic anomalies antipodal to lunar impact basins: Two‐dimensional model calculations

摘要: The production of large-scale magnetic fields and associated crustal magnetization in lunar basin-forming impacts is investigated theoretically. Two-dimensional numerical models the partially ionized vapor cloud produced such show that low-density periphery expands thermally around Moon converges near antipode a time order 400 to 500 s for silicate impactor velocities 15 20 km/s. Fields external impact plasma are by magnetohydrodynamic interaction with ambient plasmas. For most typical case which immersed solar wind its embedded field, an MHD shock wave forms upstream separating shocked from free-stream wind. occurring on downstream (antisunward) hemisphere, convergence waves occurs side results large antipodal field amplification. (sunward) some amplification still expected due finite electrical conductivity interior (requiring induced field) likely presence residual wake cloud. During period compressed amplification, seismic compressional converge at resulting transient pressures have been calculated be as 2 GPa (20 kbar). This range 50–250 kbar stable remanent has found experimentally occur soils. Significant anomalies basins therefore expected, consistent orbital mapping results. Weaker observed peripheral Imbrium basin may also explained effects together surface boundary layer. Although other processes cometary former core dynamo contributed significantly paleomagnetism, meteoroid plasmas appear capable explaining major part detected thus far orbit.