The dark side of the moon is no longer half the face of a friend. Using current gravity and topography data sets, the side of the body that never faces the Earth has the look of a palimpsest: the scars of impacts are painted over by the strains of the tectonic plate, and the structure of the rest can be determined by the manner in which the surface of the moon pulls against the orbiting spacecraft.
It has been methodological but not visual as the most consequential change. Rather than using angles of sunlight and camera geometry, researchers can now view the Moon as an object which can be observed through the mass distribution. The change came in with the twin Gravity Recovery and Interior Laboratory spacecraft of NASA, where the intersatellite ranging generated high resolution gravity measurements that were obtained by the two GRAIL spacecrafts on both sides of the planet. The difference in coverage is important: gravity does not make a distinction between an aspect on the maria on the near side and the battered highlands on the far side.
Those gravity maps not only sharpened existing outlines they redefined some fundamental assumptions of what lunar crust consists of. Highland analysis indicates a bulk density of about 2550 kg m 3 and a porosity of about 12 per cent in the upper crust, meaning that the shell is not monolithic bedrock, but rather a long-pummeled foam. In this perspective, gigantic forces are designers of underground form, not only makers of rimmed basins. The density signatures in the far side South Pole-Aitken basin, e.g., indicate that the basin is composed of more mafic materials than the rest of the terrain, a reminder that composition and history of damages are both mixed up in the gravity field.
The first implication is that now the “maps” of the far side go under the regolith. Composition is associated with density variation, with the highest basins being associated with porosity variation, which collectively bears global crustal thickness models of about 34 ,43 km on average. Hemispheric variations of the Moon, which are thinned near the side and highland on the far side, cease to be a spectacle and become a measurable constraint on interior evolution.
That greater background is redefining the interpretation of the oldest landmark in the far side. A more recent study in Nature suggests that the geometry and the magnitude of gravitational signal of the South PoleAitken basin are indicative of a southward collision, being confirmed by observable tapering in both gravity and topography and by one dimensional asymmetries in crustal-thickness gradients across one end of the basin to the other. This inference relies on uniform datasets over the whole globe; without far-side gravity, it would be the “directionality “of the basin which would stay largely a competition of drawings.
Surface mapping is also telling us that the crust of the Moon continues to move after its tremendous hits. Recently a compilation of the first global map of small mare ridges was made and 2,634 segments of mare ridges, 1,114 of them newly known, were totaled, with the majority being located in the near-side maria, and their ages were estimated to be about 124 million years. These ridges have also been connected in the work with this compressional faulting that makes lobate scarps and extends the map of the possible sources of moonquakes into terrain that might otherwise be considered relatively safe in operations in the future.
As the other side of the far side does not lack an advantage, but is silent. To do so, a relay is still needed since the hemisphere will never be directly facing the Earth; Chang-e-4 by China showed the architecture using Queqiao relay satellite and landed Yutu-2 rover into the Von Kármán crater of South Pole-Aitken. But the scientific lesson is widespread, that when gravity, composition, and tectonics can be read everywhere the hidden half of the Moon will be a less mysterious thing, and a part of it, in which the old shocks, the splintered crust, and the current shortening belong to the same table, are written upside down.
