Click to enlarge
Two NASA "twin" satellites, as part of the Grail mission, orbiting the Moon, have created the most accurate map to date of the Moon's gravity field and, more generally, of any other celestial body. Among other things, the map reveals the Moon's violent past, as repeated impacts by comets and asteroids have left their traces not only on the Moon's surface (the visible craters), but also deeper in the invisible interior of its crust. Unlike Earth, where the perpetual movement of tectonic plates, volcanic activity and soil erosion have erased the traces of ancient impacts, especially during the young age of our planet, on the Moon both its surface and interior have remained almost intact over the course of billions of years. They thus provide a geological record of violent events of the past, especially during the early phase of our solar system.
The new high-resolution map of the moon, resulting from Grail measurements, shows the fluctuations in gravity caused either by bulges (e.g. mountains) or by depressions in the ground (e.g. craters), but also by the deeper geological structures in the interior of the Moon, revealing in all its glory the "fractures" and crushing blows that the moon's crust has suffered in the past.
Scientists have found that beneath the cratered surface, the Moon's crust is almost completely pulverized (98%) by multiple impacts from various celestial bodies. The discovery suggests that our moon and possibly Earth itself, during the first billion years after their formation (at a time when the first microorganisms appeared), suffered an even more massive and destructive onslaught of huge rocks from space than scientists had previously estimated.
The new measurements show that the lunar crust is 34 to 43 kilometers thick, 10 to 20 kilometers thinner than geologists previously thought. In fact, under some flat areas, there appears to be almost no crust at all, which means that there is a "window" to the deepest geological layer, the moon's mantle, which lies between the crust and the core.
The map reveals that the upper lunar crust does not contain many dense rocks, but is mainly composed of porous materials that have been fragmented in the past. Also scattered among this lighter material are large underground linear "trenches" - up to 500 kilometers long - consisting of heavier and denser material, which probably comes from solidified magma that rose higher after the impacts.
