A slice of Mars (IMAGE) University of Tokyo Caption The three stages the researchers think the core of Mars underwent 4 billion years ago. Only during the early stage of separation would there have been an appreciable magnetic field. Credit © 2022 Yokoo et al. Usage Restrictions Credit © 2022 Yokoo et al. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.