Mare Crisium

Crisium is one of the few large maria outside the Procellarum-Imbrium system, so its fill can be dated without reference to them. At 556 km across the basin is close to circular, but it sits 59 degrees east of the meridian and foreshortening compresses it east-west, which is why it reads as an oval taller than it is wide.

It carries one of the strongest mascons on the Moon: a ring-shaped mass excess about 330 km in radius, produced by mantle uplift under the basin floor and bounded by thrust faults reaching 25 to 120 km depth. Crisium was among the first mascons identified, from tracking Lunar Orbiter in 1968.

Luna 24 landed here in 1976 and drilled to two metres, the deepest core returned from the Moon. Its basalts are very low in titanium and younger than most of the mare units Apollo sampled, extending the known span of nearside volcanism.