WHY would the compass fail to work on Mars? Mars lacks a comp | Why?

WHY would the compass fail to work on Mars?

Mars lacks a complete planetary magnetic field. There are only small magnetic anomalies, where the field is about 500 times weaker than on Earth. They are generated by magnetized rocks in the crust of Mars, not by the magnetic dynamo in the planet's core, as in the case of Earth.

Zones of magnetic anomalies are located irregularly, so that even a very sensitive compass capable of picking up their weak fields will not indicate a certain geographic direction.