Free Astronomy Magazine November-December 2014

44 MOON deduct with reasonable approximation their general composition. Thanks to this stretching and contracting “accordion” ef- fect, it was found that all around the Oce- anus Procellarum the gravitational gradi- ent presents anomalies manifesting them- selves in the form of a series of long seg- ments with intersecting angles close to 120 degrees, forming a sort of polygon. This structure only partially follows the visible borders of the ocean and shows that what appears on the surface is not a true reflec- tion of what there is deep below. The most immediate outcome of this dis- covery is that the Oceanus Procellarum cannot have originated from an asteroid T wo examples of how in the past the lava flows that filled the fractures may have looked, be- fore cooling down and being buried by subse-