Martian soil as revealed by ground-penetrating radar at the Tianwen-1 landing site

Abstract

Much of the Martian surface is covered by a weathering layer (regolith or soil) produced by long-term surface processes such as impact gardening, eolian erosion, water weathering, and glacial modifications. China’s first Martian mission, Tianwen-1, employed the Mars Rover Penetrating Radar (RoPeR) to unveil the detailed structure of the regolith layer and assess its loss tangent. The RoPeR radargram revealed the local regolith layer to be highly heterogeneous and geologically complex and characterized by structures that resemble partial or complete crater walls and near-surface impact lenses at a very shallow depth. However, comparable radar data from the Lunar far side are rather uniform, despite the two surfaces being geologically contemporary. The close-to-surface crater presented in this study shows no detectable surface expression, which suggests an accelerated occultation rate for small craters on the surface of Mars as compared to the rate on the Moon. This is probably due to the relentless eolian processes on the Martian surface that led to the burial of the crater and thus shielded it from further erosion. The high loss tangent indicates that the regolith at the Tianwen-1 landing site is not dominated by water ice.

The Dielectric Properties of Martian Regolith at the Tianwen‐1 Landing Site

“…The large deviation could be due to the heterogeneous distribution of the martian regolith along Zhurong's traveling path while the lunar regolith layer at the Chang'e‐4 landing site is relatively uniform. The TW‐1 landing site presents a larger heterogeneity in both the underground structure (Chen et al., 2023) and the permittivity distribution. It suggests that the space weathering degree (defined to include the continuous impact of large and small meteoroids and the steady bombardment of the surface by charged atomic particles from the sun and the stars.)…”

Water Ice Resources on the Shallow Subsurface of Mars: Indications to Rover-Mounted Radar Observation

“…These echo signals are then captured by the radar antenna. The data received by the radar are then analyzed to calculate the subsurface stratification and thickness of the soil on Mars (Chen et al [16]), as well as the dielectric properties of the subsurface material, such as the value of dielectric loss and relative permittivity. By determining the polarization of the radar signal, it is potentially feasible to ascertain the presence of water ice in the superficial layers of the detection area (Zhou et al [36], Dong et al [37], Liu et al [38]).…”

“…It operates at 15-95 MHz for the low-frequency channel and 450-2150 MHz for the high-frequency channel (Table 1), with thickness resolution at the meter and centimeter levels, respectively. It can be used to detect the regions with depths of tens of meters below the Martian surface (Zhou et al [15], Chen et al [16], Li et al [26]). The Perseverance rover also carries a Martian-based ground-penetrating radar, RIMFAX, primarily used to detect shallow surface geological structures and water ice on Mars [46].…”

“…However, these observations are not penetrating and only reflect the physical properties of very thin areas of the Martian surface. The Martian-based ground-penetrating radar is a unique way to explore the presence of water ice on the shallow surface layer of Mars within a few meters to tens of meters (Hamran et al [14], Zhou et al [15], Chen et al [16], Zhang et al [17]).…”

“…These missions carry advanced detection instruments, such as in situ spectrometers and highly accurate ground-penetrating radars. The Rover-mounted Subsurface Penetrating Radar (RoPeR) is onboard the Zhurong Rover (Zhou et al [15], Chen et al [16], Li et al [26]), while the Radar Imager for Mars' Subsurface Experiment (RIMFAX) is onboard the Perseverance rover (Hamran et al [14], Casademont et al [27]). Both of the Martian-based ground-penetrating radars can detect water ice within a few meters or tens of meters of the shallow surface of Mars (Hamran et al [14], Zhou et al [15]).…”