Demagnetization by Basin-forming Impacts on Early Mars: Contributions from Shock, Heating and Excavation

Introduction: When a large hypervelocity impact occurs on a planetary body such as Mars, the kinetic energy of the impactor is partitioned primarily into 1) kinetic energy of the planetary crust and mantle as they deform and flow in response to the impact, 2) heating, melting and vaporization of impactor, crust and mantle material and 3) shockwaves that travel throughout the entire volume of the planet [1]. These processes demagnetize the crust by way of 1) excavation and rotation of magnetized material, 2) thermal demagnetization and 3) shock demagnetization respectively. A key element in understanding how large impacts demagnetize the crust is the manner in which magnetic minerals lose magnetization in response to elevated temperatures and pressures. At present, little is confidently known about which minerals may be dominantly responsible for the remarkably strong Martian crustal magnetic field [2]. The best candidates are (in rank order): magnetite, hematite, pyrrhotite, titanomagnetite and titanohematite [3].