In Situ Temperatures, Regolith Properties, and Evidence of Erosion at Chandrayaan-3 Post-hop Location from ChaSTE Twilight Observations

Abstract During the final phase of the Chandrayaan-3 mission, the Vikram lander performed a successful hop experiment, relocating itself to a secondary location through engine reignition. This maneuver provided a unique opportunity to study the lunar regolith’s response to plume–surface interactions and to characterize the regolith at the secondary location. Following the hop, the Chandra’s Surface Thermophysical Experiment (ChaSTE) was redeployed to measure thermal profiles during the twilight transition (16:25–17:30 LT). Analysis of Lander Imager data confirms a displacement of approximately 50 cm from the initial site, accompanied by a slight in-plane rotation. The engine firing resulted in the removal of the uppermost 3 cm of the regolith, exposing and slightly compacting the underlying material. In situ measurements and analysis of the cooling curve reveal a distinct two-layer stratigraphy within the top 6.5 cm at the post-hop site, with the upper layer (0–3 cm) characterized by a higher bulk thermal conductivity (2.01 × 10 −2 W m −1 K −1 ) and the lower layer (3–6.5 cm) exhibiting a slightly lower thermal conductivity (1–1.2 × 10 −2 W m −1 K −1 ). Geotechnical parameters derived from penetration motor current and thermal modeling indicate significant vertical variability, with cohesion ranging from 300 to 1600 Pa and bulk density between 750 and 1600 kg m −3 . 3D model-derived temperatures for the new location show a very good agreement with ChaSTE observations. Modeled thermal profiles at varying sensor depths suggest a complex interplay between local shadowing and inherent thermophysical heterogeneity. These findings highlight the local-scale heterogeneity of the regolith in the southern polar region of the Moon, offering critical constraints for future surface operations and in situ resource utilization strategies.