Martian caves have revived interest in the field of subsurface exploration because they are the potential destinations for future human habitats and astrobiological research. There are many pits on Mars, but some of them look like collapsed cave roofs. These special pits are formed by the collapse of surface materials into the subsurface void spaces. The signature of life is probable in a subsurface cave on Mars as the subsurface environment can protect life from the harsh and dangerous radiation environment of the surface. In a cave, there may be an abundance of minerals, fluids, and other key resources. Therefore, locating the access point of the subsurface cave is essential and crucial for formulating plans for robotic/human explorations of the Red Planet, Mars. We have used remote sensing data from Mars Reconnaissance Orbiter (MRO; NASA), Mars Global Surveyor (MGS; NASA), and Mars Odyssey (NASA) for identifying, mapping, and classifying selected special pit candidates on the flank of Elysium Mons, Mars. A total of 32 special pit candidates has been identified and classified based upon morphology and geological context. Out of these, 26 are newly discovered ones. The thermal behavior of 23 special pit candidates confirms that the special pits are radiating heat energy at nighttime, similar to potential caves. Also, cave entrances have been detected in nine candidates using data from the HiRISE camera onboard MRO. These sites could be important destinations for future robotic/human exploration and the search for life on Mars.

Lunar exploration is of significant importance in the development and utilization of in situ lunar resources, water ice exploration, and astronomical science. In recent years, ground-based radar (GBR) has gained increasing attention in the field of lunar exploration due to its flexibility, low cost, and penetrating capabilities. This paper reviews the scientific research on lunar exploration using GBR, outlining the basic principles of GBR and the progress made in lunar exploration studies. Our paper introduces the fundamental principles of lunar imaging using GBR and systematically reviews studies on lunar surface/subsurface detection, the dielectric properties inversion of the lunar regolith, and polar water ice detection using GBR. In particular, the paper summarizes the current development status of the Chinese GBR and forecasts future development trends in China. This review will enhance the understanding of lunar exploration results using GBR radar, systematically demonstrate the main applications and scientific achievements of GBR in lunar exploration, and provide a reference for GBR radar in future lunar exploration missions.

China accomplished a historic milestone in 2020 when the mission Chang’e-5 (CE-5) to the Lunar’s surface was successfully launched. An extraordinary component of this mission is the “Lunar Regolith Penetrating Radar” (LRPR) housed within its lander, which currently stands as the most advanced payload in terms of vertical resolution among all penetrating radars employed in lunar exploration. This provides an unprecedented opportunity for high-precision research into the interior structure of the shallow lunar regolith. Previous studies have achieved fruitful research results based on the data from LRPR, updating our perception of the shallow-level regolith of the Moon. This paper provides an overview of the new advancements achieved by the LRPR in observing the basic structure of the shallow regolith of the Moon. It places special emphasis on the role played by the LRPR in revealing details about the shallow lunar regolith’s structure, its estimated dielectric properties, the provenance of the regolith materials from the landing area, and its interpretation of the geological stratification at the landing site. Lastly, it envisions the application and developmental trends of in situ radar technology in future lunar exploration.

The western flank of Elysium Mons, Mars, hosts a potential cave candidate (PCC) associated with a partially collapsed pit chain, previously identified in the Mars Cave Catalog. This study presents the first comprehensive investigation of the PCC, employing high-resolution imagery, thermal observations, topographic, geological, and mineralogical analyses to evaluate its structure and resource potential, and hypothesized to connect to a potential subsurface lava tube cave. High-resolution imagery from CTX and HiRISE on board the Mars Reconnaissance Orbiter (MRO), captured across varying solar angles, reveals an elliptical structure with constant shadowed regions and partial roof collapse, suggesting significant depth and consistency with a Potential Subsurface Lava Tube Skylight. Unlike the adjacent pit chain, which cools rapidly at night due to the lack of subsurface connectivity, the PCC retains heat and shows warmer appearance, indicating connectivity with the subsurface cave environment. Thermal observations from THEMIS on board Mars Odyssey confirm a pronounced night-time thermal anomaly, while topographic data from Mars Orbiter Laser Altimeter on board Mars Global Surveyor (MGS) provide detailed elevation profiles. Mineralogical analysis using Gamma-Ray Spectrometer data from Mars Odyssey identifies geochemical signatures indicative of the presence of olivine and pyroxene, iron oxides, feldspars, and potential volcanic glass. The PCC’s unique morphological, thermal, and mineralogical characteristics, along with cave entrance identification and insights from the conceptual model, highlight a potential environment for astrobiological investigations. These findings, derived from integrated data sets across MRO, Mars Odyssey, and MGS, provide crucial insights into Martian subsurface processes, resource availability, future human/robotic missions, and the planet’s potential to support life.

Lunar volcanic activity and its impact on near-surface material composition are central to lunar geological research. As of March 2024, the Yutu-2 rover has been operational on the Moon for 65 lunar days, covering a total distance of 1617.28 meters. Radar data collected by the rover during the 24th to 31st lunar days, spanning approximately 120 meters, clear horizontal reflection echoes. These reflections can be exploited for the estimation of the dielectric properties of the stratified structures. In this study, the Finite-Difference Time-Domain (FDTD) method is applied to quantitatively assess the positions and the electromagnetic properties of subsurface layers within the shallow subsurface (approximately 40 meters in depth) as detected by Yutu-2. Therefore, the paper deals with the first quantitative analysis of the positions and dielectric characteristics of four stratified layers beneath the Chang’E-4 landing site. Based on the results, the lunar layered near-surface structure is redefined in terms of a homogeneous regolith layer, an ejecta layer, a basalt layer, and a lightly weathered regolith layer. Furthermore, this study offers a detailed interpretation of the shallow geological structure at the Chang’E-4 landing site, providing potential evidence of recent volcanic activity in the region.

The Hebrus Valles region on Mars exhibits geomorphological indicators of past aqueous activity, such as fluvial channels and aligned sinkholes. While Martian skylights have mostly been linked to volcanic or tectonic origins, caves formed by water-mediated dissolution remain unexplored. This study investigates eight skylight features in Hebrus Valles as the first potential karstic cave candidates on Mars. We evaluate whether these features are indicative of collapse entrances formed through dissolution of carbonate- and sulfate-rich lithologies. To this end, the investigation is carried out by integrating mineralogical maps from the Thermal Emission Spectrometer (TES), hydrogen data from the Gamma Ray Spectrometer (GRS), and TES-derived thermal inertia and dust index maps. 3D structural modeling was performed using High Resolution Imaging Science Experiment (HiRISE)–derived Digital Terrain Models. Morphological assessments were conducted using Context Camera and HiRISE images. The skylights exhibit morphologies consistent with subsurface dissolutional collapse. TES data reveal enrichment in carbonates and sulfates near the skylights, and GRS data show elevated water-equivalent hydrogen. The skylights lie within indurated, low-dust terrains and are spatially associated with fluvial features. A 3D reconstruction from morphological data of cavity geometry is consistent with its being karstic.