摘要：Some scientific topics relating to magnetic field measurements around Mars are briefly described and specification of the magnetic field instrument onboard PLANET-B is presented. The highly elliptical orbit of PLANET-B with a periapsis altitude of 150 km and an apoapsis of 15 R M (Mars radii) will enable us to observe magnetic environments in various regions from the ionospheric altitudes to upstream and tail regions. One of the most important objectives is to resolve the controversial arguments about the magnitude of the magnetic moment of Mars. Combination of measurements with other instruments onboard PLANET-B will give us important information on unsolved problems such as the pressure balance in the dayside ionosphere and acceleration processes for ionospheric ions.
