Measurements of the Magnetism of the Mars–96 Small Station at the Nurmijärvi Geophysical Observatory

Two US spacecraft are presently exploring Mars, and several scientific Martian missions are planned for the next years. The Martian magnetic field is of great interest in many respects, and so magnetometers are included in payload plans of the missions. Since the magnetic field of Mars is very small compared with that of the Earth ( ≈ 0.1 %), fields due to the spacecraft and its instruments can es-sentially distort the recordings of a magnetometer. Incorrect interpretations and conclusions may result unless the distorting fields are known and carefully taken into account. Each of the two (identical) Small Surface Stations belonging to the Russian "Mars–96 " mission, which was launched, although unsuccessfully, in November 1996, contained a magnetometer. Before the launch, the problem of a dis-turbing magnetism of the Small Station was investigated at the Nurmijärvi Geophysical Observatory, Finland. Distortions of several tens of nanoteslas were indicated, which are of importance when measuring the weak Martian magnetic field. The main result of the work done and of this paper is that the applicability of the Nurmijärvi facilities to this kind of a “magnetic cleanliness ” study was clearly demonstrated. Due to the catastrophe of Mars–96, the scientific goals will, of course, never be reached. However, a lot of important work was done, which can directly be utilized in future Martian missions. A careful documentation of the work is therefore necessary, and this paper is a contribution about the Nurmijärvi facilities for magnetic cleanliness measurements. Key words: Martian magnetic field, magnetic cleanliness, planetary exploration 1