Chandrayaan-2 Detects Possible Subsurface Ice Near Lunar South Pole

Nearly six years after its launch in 2019, India’s second lunar mission Chandrayaan-2 continues to deliver fresh science. Scientists from the Indian Space Research Organisation’s (ISRO) Physical Research Laboratory (PRL) have reported the possible presence of subsurface ice beneath the floors of four “doubly shadowed craters” in the south-polar region of the Moon, using observations from the orbiter’s Dual Frequency Synthetic Aperture Radar (DFSAR) payload.

Doubly shadowed craters are small craters located inside larger permanently shadowed regions (PSRs). Because they are continuously shielded from direct sunlight and from thermal radiation reflected by nearby terrain, temperatures inside them can stay as low as a few tens of kelvin. Such cold and dark environments are considered ideal for preserving water-ice over geological time scales — a major reason why agencies like ISRO and NASA target the lunar south pole for future missions and bases.

Using advanced radar polarimetric analysis, the PRL team identified signatures consistent with subsurface ice. They proposed a refined criterion in which “Circular Polarization Ratio (CPR) values greater than 1, together with Degree of Polarization (DOP) values lower than 0.13,” point to volumetric scattering potentially caused by buried ice. This is significant because earlier interpretations using CPR alone could be ambiguous, as rough surface rocks can also produce high CPR.

For exam aspirants, the finding adds to the science context for India’s lunar programme. Chandrayaan-1 had earlier confirmed the presence of water on the Moon in 2008; Chandrayaan-3 successfully landed Vikram lander near the south pole in August 2023, and Chandrayaan-4 is being planned for a lunar sample-return mission. The work is also relevant to ISRO’s collaboration with international agencies such as JAXA on the LUPEX mission targeting the same region.