Layered subsurface in Utopia Basin of Mars revealed by Zhurong rover radar

Abstract

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.

Observation-based temperature field simulation at Zhurong landing site, Mars

“…As the structure of the Martian subsurface is more clearly detected by radar in Zhurong area (Li et al, 2022), more refined thermodynamic models based on the detected structure would provide more accurate results for the temperature analysis of the subsurface in this region. For example, the modeling of both the martian regolith and the filled rocks using the finite-element method can accurately simulate the temperature distribution and its variation for the martian subsurface.…”

“…It would be very helpful to analyze the underground structure and thermal state (temperature field) based on three-dimensional simulations. Although the previous study has revealed the structure of the subsurface under the Zhurong landing site (Li et al, 2022). However, the detailed threedimensional structure of the shallowest 10 m remains enigmatic.…”

“…On the near surface of Mars, the heat conduction equation can be described below (Li et al, 2022;Zhang et al, 2023b)…”

“…In the subsurface of Zhurong landing site, the absence of liquid water has been investigated by radar detection, but the existence of Frontiers in Astronomy and Space Sciences frontiersin.org ice cannot be ruled out (Li et al, 2022). Taking the case with thermal diffusivity of 1 × 10 −6 (right column, sand and/or stone) as an example, the temperature changes dramatically with the depth near the summer solstice, especially in the afternoon (14:00 LMST) and at sunset (18:00 LMST), which indicates the existence of multiphase in the medium if there is ice.…”

“…The temperature field and its seasonal variation in the subsurface layer of Zhurong landing area are very important for water/ice detection. Previous studies have conducted thermal simulations on a seasonal timescale (Li et al, 2022) for evaluating the temperature field in the subsurface based on Martian Climate Database (MCD, Forget et al, 1999). For in-situ observation-based thermal simulation, the problem is that only a short period of temperature data was collected by Zhurong during its working days; thus, the amount of recorded temperature data is inadequate for a whole-day analysis at the landing site.…”