Lunar HighlandsEdit
The Lunar Highlands constitute the largest, oldest component of the Moon’s surface. These rugged, light-toned regions surround the smoother, dark basaltic plains known as the maria, and they dominate much of the Moon’s topography on both the near side and the far side. The highlands are a record of the earliest chapters in the Solar System, preserved in rocks that are rich in plagioclase feldspar and relatively poor in the basaltic lava that formed the maria. Their study helps scientists understand the Moon’s formation, crustal evolution, and impact history, and it continues to guide modern exploration from orbiters to sample-return missions. For context, see Moon and the broader field of geology as it applies to airless worlds.
Geography and geology
Composition The highlands are best known for rocks dominated by plagioclase feldspar, particularly anorthosite, which gives these regions their characteristic light appearance. This composition points to an early phase of crust formation when crystals of calcium-rich plagioclase floated up through a global or near-global magma ocean to form a buoyant crust. The presence of anorthositic rocks is a defining signature of the highlands and a contrast to the basaltic rocks that compose the maria. For readers exploring rock types, see anorthosite and plagioclase.
Extent and morphology Covering most of the Moon’s surface—roughly the majority of its area—the highlands form a highly cratered crustal shell that is more rugged and higher in relief than the mare regions. On the near side, the highlands border and surround the vast maria basins, while on the far side they appear as expansive, heavily pitted terrain with fewer large basaltic plains. The highlands’ topography includes elevatedContinental-like regimes, mountainous complexes, and a dense population of impact craters, ranging from tiny pits to enormous basins.
Age and formation Radiometric dating of returned samples places the highland crust’s formation in the early history of the Moon, with rocks commonly dated to around 4.4 to 4.5 billion years ago. This makes the highlands among the oldest surface materials in the Solar System. The prevailing model connects crust formation to early lunar differentiation driven by the crystallization of a global magma ocean, followed by widespread bombardment that etched the crust into its current, cratered appearance. See also Magma ocean for a broader context and Lunar Highlands in relation to the Moon’s interior structure.
Notable features - Tycho and Clavius are among prominent craters in the southern highlands on the near side, illustrating the long-lived record of impacts in these regions. - The South Pole–Aitken Basin, while primarily a basin on the far side, lies within an area where the highlands interact with the deepest parts of the crust, highlighting the Moon’s asymmetrical crustal structure. - Mountain ranges and elevated plateaus in the highlands record complex tectonics and impact modification throughout lunar history. See Near side and Far side for geographic context.
Exploration and observation
Orbital and remote-sensing view The highlands have been studied extensively through orbital imagery and spectroscopy. Early missions provided global maps of albedo, color, and mineralogy, while later spacecraft refined the distribution of anorthositic rocks and the crust’s depth-dependent properties. Notable components of this body of work include data sets from LRO, Clementine (space mission), and other missions that chart geology and topography across the Moon’s surface. See also selenography for the study of lunar surface features.
Samples and laboratory analysis Rock samples returned by the Apollo program from highland regions have long informed our understanding of the Moon’s early differentiation. Analyses of highland rocks—especially those classified as anorthosites or feldspathic rocks—support the idea of an early crust formed by the floating crystal cumulate process followed by subsequent alteration and impact history. Ongoing analysis of Apollo and other mission materials continues to refine the age estimates and compositional models for the highlands. See lunar sample for more on the kinds of specimens scientists study.
Scientific significance and debates
Origin of the highland crust A central question in lunar science concerns how the highlands formed and why they dominate so much of the Moon’s surface. The prevailing account ties the highlands to early crust formation during the crystallization of a global or near-global magma ocean, producing a buoyant, feldspar-rich crust. This scenario is supported by the predominance of anorthosite-derived rocks in highland samples and by geophysical indicators of crustal thickness variations. See Lunar magma ocean and anorthosite for related topics.
Age, cratering, and surface evolution The highlands preserve an ancient record of the Solar System’s impact history. Debates exist about the timing and intensity of bombardment events, such as the Late Heavy Bombardment hypothesis, and how these events sculpted the highlands’ surfaces. While some scholars emphasize a concentrated early bombardment contributing to early crustal resurfacing, others argue for a more extended impact flux. In all cases, highland surfaces show older radiometric ages than most mare basalts, reinforcing their status as the Moon’s oldest visible terrain.
Implications for broader planetary science Understanding the highlands informs planetary differentiation and crust formation beyond the Moon, offering comparative insights for other airless bodies with ancient crusts. The study of highland rocks also provides constraints on the timing of planetary formation processes and the early thermal evolution of terrestrial planets. See planetary differentiation for a broader framework.
See also