my country plans to launch the Chang'e-7 (CE-7) lunar probe around 2026, with the goal ofLunar South Pole-Aitken Basin, detecting water ice resources in the lunar south pole, whose existence is crucial to the site selection and construction of future lunar bases.The candidate landing area for the CE-7 exploration mission is close to the Shackleton Crater at the South Pole of the Moon, and one of its important scientific tasks is to carry out high-precision remote sensing and in-place detection of water ice in the Moon's South Pole.
The (thermal) stability of water ice reflects the ease of sublimation loss of water ice on long-term, geological time scales. Evaluating the stability of water ice is of great significance to understanding the distribution characteristics of water ice in the lunar polar regions.
Especially for the CE-7 Antarctic water ice placement detection mission, research on water ice stability can guide detection and help identify areas more likely to preserve water ice.
Recently, the scientific research team of the National Key Laboratory of Solar Activity and Space Weather at the National Space Center of the Chinese Academy of Sciences (hereinafter referred to as the "Space Center") has made new progress in the study of the stability of water ice in the Shackleton region of the lunar south pole.
By considering the thermal properties of the lunar soil under low temperature conditions, the study constructed a thermal stability model of water ice in the lunar polar regions and applied it toAntarctic Shackleton Region (Figure 1), carried out a high spatial resolution simulation of the thermal stability of water ice, studied local surface radiation, lunar soil temperature, and the distribution characteristics of water ice stable areas, and discussed the significance of the simulation results for CE-7 Antarctic water ice in place detection.
Figure 1 Study area: (a) The yellow frame area is the study area, including the Shackleton crater and its surrounding areas; (b) Digital elevation model (DEM) of the study area; (c) Elevation profile of A-A’ in Figure b; (d) Slope distribution. An asterisk marks the moon's south pole.
Simulated distribution of light and thermal radiation in the study areaSee Figures 2a and 2b.
Most of the area inside Shackleton Crater is a permanently shadowed region (PSR), but the distribution of thermal radiation is uneven, while the outside of the crater is dotted with PSRs of different sizes and low-light areas.
In the Shackleton crater, the annual average surface temperature is unevenly distributed; the average temperature at the bottom of the crater is lower than in the flatter area (Figure 2c).
In addition, the simulation results of the annual average surface temperature were compared with the Diviner observation results, and it was found that compared with the Diviner results (Fig. 2d), the simulated annual average temperature in the pit was lower.
Figure 2 Illumination and surface temperature in the study area: (a) The annual maximum value of direct solar radiation, the solid lines are PSRs; (b) The annual maximum value of thermal radiation, the uncolored area is the area where the maximum value of thermal radiation is less than 2.5 W/m2; (c) The simulated annual average surface temperature, the spatial resolution inside the Shackleton Crater is ~50 m/px; (d) The annual average temperature of Diviner observation temperature, the spatial resolution is ~240 m/px. The dotted circle outlines the rim of the Shackleton crater.
Based on the simulated lunar soil temperature, the stability distribution of volatiles such as water ice can be obtained by calculating the annual average sublimation rate of water ice and comparing it with the sublimation rate limit of 100 kg/(m2·Gyr).
Figure 3 showsThe stable region of water ice and other volatiles (also known as the cold trap region) in and around Shackleton Crater.
Not only water ice traps were identified in the pit, but also cold traps of HCN, SO2 and NH3. As their sublimation temperatures continue to decrease, their cold trap area also decreases.
The identified water ice trap area is slightly larger than the water ice trap area determined by previous researchers based on the Diviner surface temperature.
In addition, according to the simulation results, HCN cold traps not only exist in some areas of the wall, but may also exist in most flat areas at the bottom of the pit.
Figure 3 Stable areas of water ice and other volatiles in Shackleton Crater and surrounding areas. The legend indicates the sublimation temperature of each volatile component.
This study considers the thermal properties of the lunar soil under low temperature conditions and constructs a thermal stability model of polar water ice.
The model can calculate the stable distribution area of light, lunar soil temperature, and water ice and other volatiles, and can be used to analyze the thermal stability of water ice in the lunar south pole, especially the CE-7 landing area, thereby determining the potential distribution area of water ice and providing important support for future CE-7 water ice detection missions.
The above research results were published in the international journal The Planetary Science Journa. The first author of the paper is Dr. Zhang Jie, special research assistant of the Space Center, and the corresponding author is researcher Liu Yang of the Space Center. This research was supported by the National Natural Science Foundation of China and the Climbing Program of the National Space Science Center.