MAVEN Magnetometer

When you navigate with a compass you can orient yourself thanks to Earth's global magnetic field. But on Mars, if you were to walk around with a compass it would haphazardly point from one anomaly to another, because the Red Planet does not possess a global magnetosphere. Scientists think that this lack of a protective magnetic field may have allowed the solar wind to strip away the Martian atmosphere over billions of years, and now NASA's MAVEN spacecraft will study this process in detail with its pair of ring core fluxgate magnetometers.