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The formation and evolution of the South Pole‐Aitken (SPA) basin is critical to relating large impact basin formation and modification to lunar geophysical evolution. Most prior models of the SPA impact were conducted in 2D, making it difficult to compare model output to the 3D crustal structure and ejecta distribution. In order to better constrain the parameters of the SPA impactor and the expected post impact distribution of crust and ejecta, we conducted numerical simulations of the SPA impact in 3D. We tested a wide range of impact parameters and constrained model results with recent geophysical data. We found the crustal structure of the SPA basin is best fit by an oblique impact (30–45°) of a 350–400 km diameter projectile impacting at 12–16 km/s. The impact excavated material from as deep as 80–120 km, and ejecta was deposited in a butterfly pattern with a forbidden region uprange of the impact. Plain Language Summary: The South Pole‐Aitken (SPA) basin is the largest impact‐generated structure on the Moon. The large size of the basin (approximately 1,500–2,000 km in diameter) implies the impact that generated the basin globally influenced the early evolution of the Moon. In order to constrain the type of impact that formed the basin, we ran computer simulations of large projectiles (300–400 km in diameter) impacting the early lunar surface. We found the structure of the crust surrounding the basin best matches an impact of a 350–400 km diameter projectile (similar in scale to Saturn's moon Mimas) impacting the Moon with a velocity of 12–16 km per second. Our computer models show that the collision that generated the basin would have formed a non‐symmetrical distribution of impact ejecta, and excavated material from the lower crust and upper mantle. Our results constrain the type of impact that formed the SPA basin, and suggest that ejecta from the impact is prevalent at sites of current and future lunar exploration. Key Points: 3D simulations constrain the South Pole‐Aitken (SPA) impactor to 350–400 km diameter impacting at 12–16 km/s and 30–45°The SPA impact excavated lower crust and upper mantle lunar materials, and emplaced ejecta in a butterfly type ejecta patternThe thick crustal annulus present in model results requires further modeling of basin collapse and post‐impact relaxation [ABSTRACT FROM AUTHOR]

Multiring basins dominate the crustal structure, tectonics, and stratigraphy of the Moon. Understanding how these basins form is crucial for understanding the evolution of ancient planetary crusts. To understand how preimpact thermal structure and crustal thickness affect the formation of multiring basins, we simulate the formation of lunar basins and their rings under a range of target and impactor conditions. We find that ring locations, spacing, and offsets are sensitive to lunar thermal gradient (strength of the lithosphere), temperature of the deep lunar mantle (strength of the asthenosphere), and preimpact crustal thickness. We also explore the effect of impactor size on the formation of basin rings and reproduce the observed transition from peak‐ring basins to multiring basins and reproduced many observed aspects of ring spacing and location. Our results are in broad agreement with the ring tectonic theory for the formation of basin rings and also suggest that ring tectonic theory applies to the rim scarp of smaller peak‐ring basins. Plain Language Summary: The largest impact craters on the Moon are multiring basins that exhibit three or more topographic rings. Great volumes of material were ejected and redistributed during the formation of these 1,000‐km‐scale basins. Formation of these basins is the predominant process driving change of the lunar crust, the outermost layer of the Moon. Why large basins have multiple topographic rings and what they might tell us about the Moon remain poorly understood. Here we simulate the formation of these basins and their rings during an asteroid impact. We explore how thickness of the lunar crust, size of the impacting body, and interior temperature of the Moon affect the formation of basins and their rings. With well‐persevered multiring basins and an abundance of high‐quality gravity and topography data, the Moon is an ideal location to explore the formation of multiring basins. A better understanding of the formation of these basins will help us understand how similar basins may have affected the crusts of the Earth, Mars, Mercury, and Venus. Key Points: We simulate the formation of multiring basins exploring the effect of impactor size, target thermal structure, and crustal thicknessOur simulations reproduce observed trends in ring spacing including the transition from peak‐ring to multiring structuresOur results show that basin ring formation is quite sensitive to target thermal structure in general agreement with ring tectonic theory [ABSTRACT FROM AUTHOR]

Abstract: The lunar geological record has much to tell us about the earliest history of the Solar System, the origin and evolution of the Earth–Moon system, the geological evolution of rocky planets, and the near-Earth cosmic environment throughout Solar System history. In addition, the lunar surface offers outstanding opportunities for research in astronomy, astrobiology, fundamental physics, life sciences and human physiology and medicine. This paper provides an interdisciplinary review of outstanding lunar science objectives in all of these different areas. It is concluded that addressing them satisfactorily will require an end to the 40-year hiatus of lunar surface exploration, and the placing of new scientific instruments on, and the return of additional samples from, the surface of the Moon. Some of these objectives can be achieved robotically (e.g., through targeted sample return, the deployment of geophysical networks, and the placing of antennas on the lunar surface to form radio telescopes). However, in the longer term, most of these scientific objectives would benefit significantly from renewed human operations on the lunar surface. For these reasons it is highly desirable that current plans for renewed robotic surface exploration of the Moon are developed in the context of a future human lunar exploration programme, such as that proposed by the recently formulated Global Exploration Roadmap. [Copyright &y& Elsevier]

While the surface missions to the Moon of the 1970s achieved a great deal, scientifically much was also left unresolved. The recent plethora of lunar missions (flown or proposed) reflects a resurgence in interest in the Moon, not only in its own right, but also as a record of the early solar system including the formation of the Earth. Results from recent orbiter missions have shown evidence of ice or at least hydrogen within shadowed craters at the lunar poles. [ABSTRACT FROM AUTHOR]

Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission indicate a marked change in the gravitational signature of lunar impact structures at the morphological transition, with increasing diameter, from complex craters to peak-ring basins. At crater diameters larger than ~200 km, a central positive Bouguer anomaly is seen within the innermost peak ring, and an annular negative Bouguer anomaly extends outward from this ring to the outer topographic rim crest. These observations demonstrate that basin-forming impacts remove crustal materials from within the peak ring and thicken the crust between the peak ring and the outer rim crest. A correlation between the diameter of the central Bouguer gravity high and the outer topographic ring diameter for well-preserved basins enables the identification and characterization of basins for which topographic signatures have been obscured by superposed cratering and volcanism. The GRAIL inventory of lunar basins improves upon earlier lists that differed in their totals by more than a factor of 2. The size-frequency distributions of basins on the nearside and farside hemispheres of the Moon differ substantially; the nearside hosts more basins larger than 350 km in diameter, whereas the farside has more smaller basins. Hemispherical differences in target properties, including temperature and porosity, are likely to have contributed to these different distributions. Better understanding of the factors that control basin size will help to constrain models of the original impactor population.