Mars's weak magnetic field suggests it had stronger fields in the past, and magnetic measurements made by rovers and orbiters imply the planet may have undergone several polarity reversals over its history.
Mercury may have undergone a field reversal about 800 million to 2 billion years ago as inferred from magnetic anomaly data collected by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission . However, this interpretation remains contested.
