Linear magnetization feature associated with Rima Sirsalis

Abstract

Measurements of the magnetic fields by the electron reflection method in the neighborhood of the long structural rille Rima Sirsalis show that a magnetic field with a strength of at least 100 nT (100 gammas) is present over a region of the order of 10 km in width and at least 300 km long. The center of the magnetized region closely parallels and is centered on the rille. The linear magnetization feature extends at least to latitude 8 deg S, 60 km beyond the place where the rille disappears at the edge of Oceanus Procellarum. This extension is coincident with the extrapolation of the rille based on photographs. However, the magnetization is much weaker or entirely absent at 5 deg S and has vanished at 0 deg latitude. These results suggest that the rille is indeed a structural feature and has associated with it magnetization, either in the form of intrusive magnetized rock or of a gap in an otherwise more or less uniformly magnetized layer of rock of large extent in two dimensions. Furthermore, the rille structure evidently is present for some distance beneath the lava flows of the Oceanus Procellarum basin.