THE PRODUCTION AND EVOLUTION OF IMPACT-GENERATED MAGNETIC-FIELDS

The production of magnetic fields within impact-generated plasma may explain magnetic fields that have been observed during hypervelocity impact experiments at the NASA Ames Vertical Gun Range. The effect of impact angle on the production and subsequent evolution of impact-generated magnetic fields is assessed using magnetic field data obtained during macroscopic hypervelocity impacts conducted within two ambient magnetic field environments. The configuration and duration of spontaneous impact-generated magnetic fields are found to have a strong dependence on impact angle, exhibiting a smooth transition from a cylindrically symmetric field configuration at vertical incidence to a strong bilaterally anti-symmetric field configuration at high obliquity; hence, crater-related paleomagnetic fields may yield a diagnostic signature of impact angle where other clues (shape, ejecta pattern) are absent or ambiguous. As a direct result of some surprising experimental results, a first-order model of field generation during the cavitation regime of high incidence angle hypervelocity impacts is explored. A possible consequence of this model is that magnetic fields produced during hypervelocity impacts (especially those that form large craters) may be an important component of planetary magnetism-especially lunar magnetism during the last -3.6 billion years.