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Recent findings from India’s Chandrayaan-3 mission suggest that hidden reserves of water ice beneath the moon’s surface may be more abundant than previously believed. These reserves could be crucial for future astronauts, providing drinking water, cooling equipment, producing oxygen, and even fueling deep-space missions.
The Indian Space Research Organisation’s (ISRO) Chandrayaan-3 successfully soft-landed near the Moon’s south pole on August 23, 2023. The study, published in the journal Communications Earth & Environment, is based on data gathered by Chandra’s Surface Thermophysical Experiment (ChaSTE), a payload aboard Vikram, the mission’s lander module.
Understanding the Moon’s Thermal Environment
The ChaSTE payload was designed to measure the temperature and thermal conductivity of the lunar surface. It conducted surface measurements near the landing site, providing temperature readings for the top 10 centimeters of regolith and assessing the thermal conductivity in the Moon’s southern polar region. Regolith refers to the layer of rock fragments covering airless celestial bodies like the Moon.
“ChaSTE experiment onboard Vikram lander of Chandrayaan-3 has provided the first in-situ temperature profiles near south polar region of the Moon, as per the best of our knowledge,” researchers from India wrote in the study. Previously, such measurements were only available from equatorial regions where NASA’s Apollo missions had landed.
The study emphasized that the local thermophysical environment plays a significant role in determining the presence and stability of water ice on the Moon. The ChaSTE experiment aimed to explore these environmental factors at the landing site to better understand the conditions that allow water ice to remain stable at or beneath the surface.
Why Water Ice Matters for Future Missions
The presence and stability of water ice on the Moon depend on local thermophysical conditions. Earlier studies indicated that surface temperatures between -163.15°C and -159.15°C favor the presence of water ice, particularly in polar regions. Researchers also hypothesized that water ice could migrate deeper into the subsurface.
ChaSTE began collecting data on the second day after landing and continued measurements until September 2, 2023. The payload penetrated the lunar soil to analyze temperature variations.
The results were surprising—temperatures near the lunar south pole were higher than expected. The Sun-facing slope at an angle of 6° recorded a peak temperature of 82°C and dropped to -168°C during the lunar night. Meanwhile, a flat region about one meter from the lander recorded a lower peak temperature of 59°C.
Surprising Temperature Findings
“The higher temperatures measured at this high-latitude location were quite surprising, although our pre-landing estimates predicted higher temperatures. However, we did not anticipate that surface temperatures can show significant variability within metre scales.
This is completely a new insight about temperatures and thermophysics on the Moon and needs more detailed investigations in future,” said K Durga Prasad, faculty and principal investigator of ChaSTE (PRL), Planetary Sciences Division at the Physical Research Laboratory, in an interview with Down To Earth.
ChaSTE’s findings suggest that high surface temperatures make water ice on the surface unstable. However, the study also indicates that certain conditions, such as slope angles and Sun exposure, influence temperature and thermophysical properties, potentially allowing water ice to remain stable in some areas.
Where Could Water Ice Be Stable?
Researchers modeled solar flux and diurnal temperature variations at different slope angles to determine where water ice might be most stable. Sun-facing slopes were unlikely to support stable water ice, but steeper poleward slopes—exceeding 14°—provided better conditions.
At a 14° slope, maximum and minimum temperatures were recorded at -37.15°C and -199.15°C, suggesting that water ice could remain stable at a depth of up to one meter. At an 18° slope, maximum and minimum temperatures of -120.15°C and -206.15°C indicated that water ice might even be stable at the surface and subsurface within a meter.
ChaSTE also revealed that nearby slopes facing away from the Sun could be much cooler than Sun-facing areas just a meter apart, creating an environment conducive to the presence of water ice in the shallow subsurface.
Implications for Future Moon Exploration
“The ChaSTE measurements provide a lot of new information about the temperature distribution within the outermost 10 cm regolith layer of lunar high-latitude highlands,” the researchers wrote in the study. These high-latitude areas are promising locations for water ice prospecting, resource utilization, and future human habitation.
These regions also pose fewer technical challenges compared to areas closer to the Moon’s poles, making them more accessible for exploration.
Looking ahead, researchers aim to study different locations to determine the presence and quantity of water ice. They also emphasize the need for a deeper understanding of the lunar water cycle and its variations over time, which could aid in future human and robotic exploration efforts.
