Nearly six years after its launch, India’s Chandrayaan-2 mission continues to deliver significant scientific insights into the lunar surface. Researchers have identified potential signs of subsurface ice in the Moon’s south polar region through data gathered by the orbiter’s instruments.
A team of scientists from the Physical Research Laboratory (PRL) analysed observations from the Chandrayaan-2’s Dual Frequency Synthetic Aperture Radar (DFSAR) payload. Their study focused on doubly shadowed craters situated within permanently shadowed regions (PSRs) near the lunar south pole. These unique craters remain shielded from sunlight and thermal radiation, maintaining extremely low temperatures around 25K, conditions highly favourable for the long-term preservation of water ice.
Using advanced radar polarimetric techniques, the researchers detected signatures consistent with subsurface ice beneath the floors of four such doubly shadowed craters. According to ISRO, the analysis employed a refined radar-based criterion: areas showing a Circular Polarization Ratio (CPR) greater than 1 combined with a Degree of Polarization (DOP) lower than 0.13 suggest volumetric scattering that may be linked to the presence of subsurface ice.
The DOP parameter helps measure how much of the radar signal maintains its original polarisation after interacting with surface or subsurface materials. This method allows scientists to differentiate genuine ice-related signals from those produced by rough, rocky terrain.
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Among the craters examined, one measuring 1.1 km in diameter located inside the Faustini crater provided particularly compelling evidence. Radar data for this feature was supported by its distinctive lobate-rim morphology a flow-like appearance around the crater rim which suggests the impact may have interacted with underlying ice deposits.
These findings offer valuable new understanding of the distribution of lunar polar volatiles. They carry important implications for upcoming lunar exploration efforts, particularly in identifying promising sites for future landings and in-situ resource utilisation (ISRU) activities that could support sustained human presence on the Moon.
Chandrayaan-2 was launched in July 2019. While the Vikram lander experienced a communication loss during its attempted soft landing on September 7 that year, the orbiter remains fully operational with all eight payloads, including the DFSAR instrument, functioning effectively.