The researchers who study the lunar surface have come across an unexpected discovery: from the data on the lunar topography it emerges that there is a gravitational "anomaly" in correspondence with a large crater in the South Pole region, which seems to contain a large deposit of material dense, presumably the remains of an ancient metallic asteroid.
The area, known as South-Aitken basin, is one of the largest known impact craters: it has a diameter of 2500 kilometers. There have been even larger impacts (including some on earth), but the rarefied lunar atmosphere retains these traces much better and for a long time: that's why that area has always been the subject of research. The Chinese lander Chang'e recently visited the area, stationed in a small crater called Von Kármán.
A team from Baylor University in Texas used data from the 2011 and 2012 Gravity Recovery and Interior Laboratory (GRAIL) missions, and from the Lunar Reconnaissance Orbiter (LRO), which monitored the area for 10 years, to formulate new hypotheses about the origin of the crater. Taken together they have an oddity: in the crater area the gravity should decrease slightly, while it actually increases.
The most plausible explanation is that the object responsible for the impact is still there, almost intact beneath the surface. 4 billion years ago a largely metallic asteroid hit our satellite and was buried there.