No abstract

Ina, a distinctive ~2 × 3 km D‐shaped depression, is composed of unusual bulbous‐shaped mounds surrounded by optically immature hummocky/blocky floor units. The crisp appearance, optical immaturity, and low number of superposed impact craters combine to strongly suggest a geologically recent formation for Ina, but the specific formation mechanism remains controversial. We reconfirm that Ina is a summit pit crater/vent on a small shield volcano ~3.5 billion years old. Following detailed characterization, we interpret the range of Ina characteristics to be consistent with a two‐component model of origin during the waning stages of summit pit eruption activities. The Ina pit crater floor is interpreted to be dominated by the products of late‐stage, low‐rise rate magmatic dike emplacement. Magma in the dike underwent significant shallow degassing and vesicle formation, followed by continued degassing below the solidified and highly microvesicular and macrovesicular lava lake crust, resulting in cracking of the crust and extrusion of gas‐rich magmatic foams onto the lava lake crust to form the mounds. These unique substrate characteristics (highly porous aerogel‐like foam mounds and floor terrains with large vesicles and void space) exert important effects on subsequent impact crater characteristics and populations, influencing (1) optical maturation processes, (2) regolith development, and (3) landscape evolution by modifying the nature and evolution of superposed impact craters and thus producing anomalously young crater retention ages. Accounting for these effects results in a shift of crater size‐frequency distribution model ages from <100 million years to ~3.5 billion years, contemporaneous with the underlying ancient shield volcano.

More than 3 million range measurements from the Chang'E-1 Laser Altimeter have been used to produce a global topographic model of the Moon with improved accuracy. Our topographic model, a 360th degree and order spherical harmonic expansion of the lunar radii, is designated as Chang'E-1 Lunar Topography Model s01 (CLTM-s01). This topographic field, referenced to a mean radius of 1738 km, has an absolute vertical accuracy of approximately 31 m and a spatial resolution of 0.25 o (~7.5 km). This new lunar topographic model has greatly improved previous models in spatial coverage, accuracy and spatial resolution, and also shows the polar regions with the altimeter results for the first time. From CLTM-s01, the mean, equatorial, and polar radii of the Moon are 1737103, 1737646, and 1735843 m, respectively. In the lunar-fixed coordinate system, this model shows a COM/COF offset to be (−1.777, −0.730, 0.237) km along the x, y, and z directions, respectively. All the basic lunar shape parameters derived from CLTM-s01 are in agreement with the results of Clementine GLTM2, but CLTM-s01 offers higher accuracy and reliability due to its better global samplings.Chang'E-1, laser altimeter (LAM), lunar topographic model