Lightning remagnetization of the Vredefort impact crater: No evidence for impact‐generated magnetic fields

A new paleomagnetic study challenges the long-standing hypothesis that the Vredefort impact crater in South Africa preserves evidence of impact-generated magnetic fields. By analyzing subsurface samples from two 10-meter deep boreholes, researchers found magnetization consistent with thermoremanent acquisition in Earth's geomagnetic field post-impact, rather than exotic impact-related processes. Surface rocks, however, exhibit intense and randomly oriented magnetization linked to recent lightning strikes. This finding undermines a key argument for impact-generated fields as an alternative to dynamo mechanisms in extraterrestrial paleomagnetism, particularly on the Moon and asteroids. The study leverages subsurface sampling to distinguish between lightning-induced and impact-related magnetic signatures, providing critical insight into the magnetization history of one of Earth's oldest craters.

Carporzen, L., Weiss, B. P., Gilder, S. A., Pommier, A., & Hart, R. J. (2012). Lightning remagnetization of the Vredefort impact crater: No evidence for impact‐generated magnetic fields. Journal of Geophysical Research: Planets, 117(E1). Portico. https://doi.org/10.1029/2011je003919