Mars Global Surveyor detects crustal magnetism (1998)
NASA's Mars Global Surveyor orbiter detected strong, banded crustal magnetic fields in Mars's southern highlands. The fields were fossil magnetization, frozen into the rock when Mars's own global magnetic field died.
The discovery established that Mars had an early dynamo that shut down early in the planet's history, leaving only crustal magnetic traces.
It shaped decades of work on how small planetary bodies generate and lose magnetic fields, providing a template for reading dead dynamos from orbit.
The lunar study uses the same principle: read fossil magnetization in crustal rock to infer a dynamo that no longer runs.
