Extended Data Fig. 2: Schematic illustration of the thermal conduction model setup and modeled temperature profiles on the Moon’s nearside and farside hemisphere.

a shows the model setups with different Th contents and megaregolith thickness of nearside and farside hemisphere. The crust of the nearside or of the PKT region (dark red) has a thickness of 30 km with Th concentration of 5.5 ppm, covered by an ejecta layer (see refs. ^88,89,90,93) with a thickness (h_r) of 1 km. The farside crust (light blue) of case 1 has an upper crustal thickness of 30 km with a Th concentration of 0.5 ppm and a lower crustal thickness of 10 km with a Th concentration of 5 ppm, with the top of crust being covered by an ejecta layer with a thickness of 1 km; for case 2, the farside has a Th concentration of 0.5 ppm for the entire crust of 40 km, covered by a megaregolith layer with thickness of 5 km (see refs. ^{14,101,102,122}). In a, the numbers in orange represent the Th content of lower crust and megaregolith thickness for farside crust of case 2. The thermal conductivities of the ejecta/megaregolith layer (k_r), crust (k_c), and mantle (k_m) are assumed to be 0.3, 2, and 3 W k⁻¹ m⁻¹, respectively. b shows the modeled temperature profiles of the upper 100 km of the Moon for the nearside at 50 (cyan), 100 (green), and 150 (red) Myr after t_LMO. c and d show the modeled temperature profiles of the farside at 50 (cyan), 100 (green), and 150 (red) Myr after t_LMO for case 1 and case 2 scenario, respectively. The horizontal dashed line in b, c, and d marks the crust-mantle boundary; the vertical dashed line marks 1,200 K, the critical temperature above which the lower crust may viscously flow; the black solid lines are solidus for the crust and mantle that are used as the initial temperature profiles for our simulations. The gray dashed-dot line in b and c represents the temperature profile of 10 K km⁻¹ used for impact cratering simulations in this work; the blue dashed line in c represents the temperature profile of 50 K km⁻¹ used for the SPA-forming impact simulation in Trowbridge et al.⁴¹.