EAPS DLS Department Highlight Series: Rona Oran
Impact Plasmas and Ancient Dynamos: Addressing the mysteries of lunar magnetism
The crusts of Moon, Mars, Mercury, and meteorite parent bodies contain remanent magnetization thought to be records of past core dynamos. The Moon constitutes a unique laboratory for understanding the dynamo process because of the apparently strong and long-lived magnetic field. In particular, paleointensity estimates from Apollo samples seem to require a power source ~100 times larger than what could be continuously supplied by an Earth-like thermochemical dynamo. This motivated the alternative proposal that the source of magnetization is not a dynamo at all, but rather fields induced by the solar wind field and impact plasmas that are recorded by heated and shocked rocks. To assess this, we conducted the first study combining impact-physics and magnetohydrodynamic simulations. We found that impact-amplified fields are ∼1,000 times weaker than the Apollo paleointensities, demonstrating that the Moon was not magnetized solely by external fields. Because this still leaves the high paleointensities unexplained, we are currently exploring the possibility of a hybrid model in which impact plasmas could amplify a dynamo field. This model might also explain magnetization on other airless bodies.
About this Series
The Department Lecture Series at EAPS at MIT is a series of Weekly talks given by leading thinkers in the areas of geology, geophysics, geobiology, geochemistry, atmospheric science, oceanography, climatology, and planetary science. For more information please contact: Maggie Cedarstrom, firstname.lastname@example.org.