This instrument pair will attempt to measure the poorly understood global magnetic properties of Mars. On Earth, an extremely powerful magnetic field surrounds the planet. The magnetism results from an enormous amount of molten iron churning at the center of the Earth.

In comparison, data returned from previous Mars missions indicates that the Martian magnetic field is extremely weak and almost non-existent. By looking at data from Surveyor's magnetometer and electron reflectometer, scientists hope to learn about the interior composition of Mars. Such a study will also yield insight into the history of the geophysical forces that shaped Mars. Scientists hope to learn how those forces differed from those that shaped the Earth.

Unlike the other instruments, the magnetometer is not attached to the main body of the spacecraft. Instead, each one of the magnetometer's two sensors sit at opposite ends of the spacecraft at the ends of Surveyor's two solar arrays. This placement ensures that the data generated from the magnetometer sensors will not be "polluted" by the magnetic signal from the spacecraft.