http://messenger.jhuapl.edu/annotated-20030724.html

MESSENGER Mission News
Eyeing The Field
August 1, 2003

The tool designed to answer key questions about Mercury's magnetic field -- the MESSENGER Magnetometer instrument -- is coming together on the spacecraft. Last week the spacecraft team installed and tested the electronics box for MESSENGER's Magnetometer - a necessary step before the team can install the instrument itself. Eventually the Magnetometer sensor will be mounted on a 3.6-meter (nearly 12-foot) boom that will keep it away from the spacecraft's magnetic field. In this view the Magnetometer electronics box is on the bottom of the spacecraft, close to where the engineers can be seen in the lower left.

Mercury's magnetic field (at the surface of the planet) is about 1,000 times weaker than Earth's. The Magnetometer will characterize Mercury's magnetic field in detail from orbit over four Mercurial years -- each 88 Earth days - helping scientists determine the field's exact strength and how that strength varies with position and altitude. This will provide crucial clues to help us determine the internal source of Mercury's magnetic field.