Old crust still magnetized by a dynamo that died billions of years ago.
Terra Cimmeria is an ancient southern highland famous for hosting some of Mars's strongest crustal magnetic anomalies. These striped magnetic signatures are fossils of a global magnetic field that Mars lost billions of years ago, locked into the rock as it cooled.
Claim your plot here →When Mars was young it had a churning molten core that generated a global magnetic field. Terra Cimmeria's ancient crust cooled while that field was active, freezing in intense, banded magnetic anomalies that spacecraft still detect today — some of the strongest on the planet.
The field itself vanished roughly four billion years ago when the core dynamo shut down, stripping Mars of magnetic protection and helping the atmosphere erode away. Terra Cimmeria's striped magnetism is therefore a crucial record of a lost dynamo and a clue to why Mars became the cold, dry world it is now.