Exploring the subsurface structure and stratification of Mars advances our understanding of Martian geology, hydrological evolution and palaeoclimatic changes, and has been a main task for past and continuing Mars exploration missions1–10. Utopia Planitia, the smooth plains of volcanic and sedimentary strata that infilled the Utopia impact crater, has been a prime target for such exploration as it is inferred to have hosted an ancient ocean on Mars11–13. However, 45 years have passed since Viking-2 provided ground-based detection results. Here we report an in situ ground-penetrating radar survey of Martian subsurface structure in a southern marginal area of Utopia Planitia conducted by the Zhurong rover of the Tianwen-1 mission. A detailed subsurface image profile is constructed along the roughly 1,171 m traverse of the rover, showing an approximately 70-m-thick, multi-layered structure below a less than 10-m-thick regolith. Although alternative models deserve further scrutiny, the new radar image suggests the occurrence of episodic hydraulic flooding sedimentation that is interpreted to represent the basin infilling of Utopia Planitia during the Late Hesperian to Amazonian. While no direct evidence for the existence of liquid water was found within the radar detection depth range, we cannot rule out the presence of saline ice in the subsurface of the landing area.

Detailed knowledge of the lithospheric structure is essential for a better understanding of the tectonic evolution of the Xing'an‐Mongolian Orogenic Belt (XMOB). We constrained the lithospheric structure across the XMOB by receiver function imaging and shear wave splitting analysis from a dense seismic array. The lithosphere‐asthenosphere boundary (LAB) is coherently imaged in different tectonic blocks. The mid‐lithospheric discontinuity is also identified at ∼75–100 km depth over the deeper LAB (∼110–130 km) beneath the western side of the North‐South Gravity Lineament (NSGL), roughly at the same depth as the LAB beneath the eastern side of the NSGL. The distinct variations in both the lithospheric structure and fast shear‐wave polarization direction across the NSGL are likely caused by different tectonic processes in the two sides, indicating that the NSGL might represent the western boundary influenced by the subduction of the (Paleo‐)Pacific Plate. Lithosphere thinning in the XMOB is evidenced to have been limited mainly to the east of the NSGL.

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