Mars — a planet in magnetic transition?

Planet Mars is currently an object of increasing scientific and public interest. Several spacecraft are on their way or planned to be sent to our neighbour planet to unravel its secrets. One of the most unknown properties of planet Mars is whether it possesses a planetary magnetic field of dynamo origin. Observed weak surface magnetic fields seem to argue against a currently operating planetary dynamo. However, weak surface fields are also expected if a polarity reversal occurs. We shall discuss arguments in favour and against the speculation that Mars still operates an active dynamo with the weak surface magnetic fields pointing towards an ongoing reversal. As the possible way to validate this speculation we discuss the importance of a spherical harmonic expansion of the Martian magnetic field. The planned NetLander project and its anticipated magnetic field measurements are a powerful tool to provide at least a low-order spherical harmonic expansion coefficient determination of the Martian magnetic field, thereby allowing to study characteristics of crustal magnetic field anomalies as well as giving clues to the question whether Mars is a planet in magnetic transition.