Abstract:

Impacts play a key role in shaping planetary formation, and evolution at various stages. During the planet formation phase, growing planets experience a number of large impacts that set the initial states of the planets. After the main accretion phase, these planets continue to experience smaller impacts that deliver volatiles and shape the planetary surface environment. In this presentation, we will cover two topics: (1) the effects of impacts on Earth’s magnetic field, and (2) searching for evidence of impact bombardment on Earth. For the first topic, previous studies suggest that a large impact could kill a planetary dynamo, while other studies indicate the opposite. In this work, we investigate the effects of impacts on the planetary dynamo focusing on the canonical Moon-forming impact and smaller impacts as case studies. We conduct impact simulations using the smoothed particle hydrodynamics (SPH) method combined with a thermal and magnetic evolution model. We find that the canonical Moon-forming impact could kill the dynamo briefly (for ~1000 years), but the dynamo recovers quickly afterwards. In contrast, the recovery time is much longer for the smaller impact scenarios. For the second topic, we aim to understand early Earth’s crust formation process using the Sudbury impact basin, which hosts the largest preserved melt sheet, as an analogue site. Based on our impact simulations with iSALE and machine learning model of zircon trace element abundances, we find that most of early Earth’s zircons did not form through impact processes, suggesting that the zircons preserved from early Earth’s crust do not provide evidence of impact bombardment.

Speaker: Dr. Miki Nakajima (University of Rochester)

Host: Christine Houser, ELSI.

Date: Wed. 28 October 15:30-16:30 JST

Venue: Mishima Hall, ELSI (Hybrid)