GRAIL gravity gradients evidence for a potential lava tube at Marius Hills on the moon

Lunar lava tubes are underground channels formed by volcanic eruptions and lava flow during the Moon's volcanic period. Intact lunar lava tubes have the potential to serve as secure shelters for humans and facilities, as they provide a safe and pristine environment with a constant temperature. In this study, the lunar gravity field model derived from NASA's GRAIL mission data is analyzed for detecting of an empty lava tube in the Marius Hills region. Compared to the classical Hessian matrix, the gravitational gradient method used in this study is capable of detecting anomaly signals both in the north-south and east-west directions. Using this method, we detect a north-south anomaly signal in the Marius Hills region, located at 57.5(degrees)W and 14.3(degrees)N, indicating a negative density anomaly near the known lunar sinuous rilles and the Marius Hills Hole skylight. This suggests the presence of a potential lava tube, which is confirmed by the results of the forward method and lunar radar echo data. The extent of the lava tube is estimated with the forward method to be similar to 60 km in length, similar to 9 km in width, similar to 605 m in depth, and similar to 55 m in height. Furthermore, the gradient features indicate that the skylight located on the eastern side of the lava tube could serve as an entry to the main part of the lava tube.