A 50-degree spherical harmonic model of the magnetic field of Mars

This paper presents a 50-degree and order spherical harmonic model of the m agnetic field of Mars derived at 120-km altitude using the three orthogonal components of the vector magnetic field data acquired by the Mars Global S urveyor within the 80- to 200-km-altitude range. The downward continued vec tor magnetic field components to the surface of Mars delineate details of t he Martian magnetic field. The strong magnetic anomalies in the southern he misphere do not show compelling evidence for magnetic lineations similar to those associated with the seafloor spreading on Earth. The anomalies are m ore or less equidimensional. The magnetic signatures surrounding the impact basins Hellas, Argyre, and Isidis show that the prominent magnetic anomali es are older than the impact events. An average magnetization of similar to 2 A/m is estimated for the upper crust surrounding Hellas basin. Four isola ted magnetic anomalies are modeled by vertical prisms with circular cross s ections of 170- to 190-km radius and 20- to 30-km thickness. The magnetizat ion of the model prisms is 5 A/m more than that of the surroundings.