Results from India’s Chandrayaan 3 lander show below-freezing conditions exist farther from the poles than expected.
Chandrayaan 3
Chandrayaan 3
Deep craters close to the Moon’s poles were long thought to be the best bet for human exploration and settlement. Lunar orbiters and even a lunar impactor have shown that the permanently shaded crater floors stay cold enough to preserve deposits of water ice. Astronauts could mine that ice for drinking water and rocket fuel.
Now, in a turn of good luck for human lunar missions, new analysis of data from India’s Chandrayaan 3 lander, which touched down on the lunar surface on August 23, 2023, indicates that deposits of ice might exist farther away from the poles than expected. These places might be more accessible to future astronauts.
The lander touched down on the Moon at 69°S — the southernmost landing ever at that time. It then inserted a temperature probe 10 cm (4 inches) deep into the lunar regolith. Fitted with 10 sensors at different depths, the probe continuously monitored temperature changes over the full duration of the mission, collecting 12 days of precise measurements.
To the team’s surprise, the temperatures were significantly higher than had been predicted based on detailed thermodynamic modeling of the site. Meanwhile, a sensor directly under the lander, just a meter away from that probe, found a surface temperature 23K (40°F) cooler. After careful analysis, the researchers determined that the slight sunward-facing slope of the ground caused the higher temperature readings.
“We know that the top layer of the moon is highly space weathered and has extremely low thermal conductivity and a very high porosity, so because of that it may act as a thermal blanket,” says K. Durga Prasad (Physical Research Laboratory, India), who led the study published March 6th in Communications Earth & Environment.
When Prasad and his team found that the temperatures measured by the probe were higher than their detailed modeling had predicted, he says, “that was a little surprising for us.” After carefully checking all the inputs and conditions in the model, they realized the local topography might be playing a role. By analyzing the images and inclinometer data, they saw that while the area right under the lander was flat, the area just to the side where the thermal probe was located was inclined toward the Sun by six degrees.
The Pragyan rover captured the image of the Vikram lander of the Chandrayaan 3 mission, shown in frame (a). From this image, the team reconstructed a model, shown in (b) for their simulations. In frame (c), the team has reconstructed the surface, with an exaggeration by a factor of 5 for better visualization of details.
Communications Earth & Environment 2025
Running their model again and including the inclination data yielded results that matched the observations well, Prasad says.
Using this new understanding of the relationship between the surface angle and temperature, they were able to calculate that for locations this far from the pole, slopes tilted 14° or more away from the Sun would stay cool over the long term, with maximum daytime temperatures in the soil never exceeding 30°F (-1°C), just below the freezing point of water.
“These are conducive temperatures for the accumulation of water ice,” Prasad says. In fact, the temperature profiles are similar to those calculated for permanently shaded craters near the pole. “This is the first in-situ measurement which has shown that temperatures can significantly change within a meter scale because of local topography.”
The fact that such conditions are found farther from the pole than expected is important, he adds, because landing and operating at those locations would be easier than at the pole, where solar illumination for power generation is limited and landing zones are narrower.
Chandran Kumar (Physical Research Laboratory, India), a coauthor of the new research, says that developing the temperature sensor was difficult, because it needed to be able to span a range of 400 kelvin in its readings, while maintaining a precision of just 0.3 K. “That was one of the pretty difficult tasks for us,” he says. The instrument also had to last for the duration of the mission under the harsh lunar conditions. The innovative sensor they developed will be the subject of a future paper, he says.
Timothy McClanahan (NASA Goddard), who has published earlier research on lunar temperature profiles, tells Sky & Telescope, “I was rather surprised at how much thermal variability at 10 centimeters there was,” since thermal modeling had predicted much less of a change. “That suggests that the thermal variation goes on into further depths as you go into the subsurface, and that has an important impact on the possibility for storing water ice.”
To follow up on these findings, he suggested, “it would be great to have a rover or a hopper or some other mobile system that can go investigate permanently sheltered regions as well as poleward-facing slopes, to evaluate and assay those locations.” And that’s something that’s likely to happen as part of NASA’s Artemis program, he says.
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