New Insights into Lava Tube Formation: An Asymmetrical and Deep Case Observed by Yutu-2 Radar at Lunar Farside

Abstract This article reports a potential lava tube observed at ∼130 m depth of the lunar farside by Lunar Penetrating Radar data. However, a possible scenario with a kind of dry and low-density materials connected with a basaltic boulder or lava flow cannot be excluded. If the lava tube is valid, it is at the edge of a huge paleo-depression with a maximum width of ∼26 m and a height of ∼16 m. It presents bright and phase-reversed reflections, a depressed roof, and asymmetrical reflected power on the radargram. Estimation results of the loss tangent provide evidence for it and simultaneously reveal the residual basalt material in the western region of the tube. The ancient lava flow is thought to postdate the adjacent ejecta and has high FeO+TiO 2 content. Comprehensive analyses demonstrate that the lava flow inflation, the looseness of the adjacent ejecta, and the depressed paleo-terrain may cause horizontal erosion, subsequent deceleration, and final residue of the lava. Subsequent differential compaction of overlying strata resulted in its deformation and the accumulation of pyroclastic materials in it. The results may provide unprecedented knowledge about the formation mechanisms and interior structures of lava tubes on the Moon.