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Chandrayaan-2 finds possible subsurface ice on Moon. What we know
Since these regions are continuously shielded from both sunlight and thermal radiation, temperatures there remain extremely low, around 25 Kelvin.
Scientists studying data from India’s Chandrayaan-2 mission has provided new evidence pointing to the possible presence of ice beneath the Moon’s surface near its South Polar Region. The findings come from a detailed analysis carried out by researchers at the Physical Research Laboratory (PRL), Ahmedabad, using observations from the Chandrayaan-2 orbiter’s Dual Frequency Synthetic Aperture Radar (DFSAR).
The research focused on permanently shadowed regions (PSRs) near the lunar south pole — areas that never receive sunlight and remain among the coldest places in the solar system. Within these regions, scientists closely examined what they describe as “doubly shadowed craters,” small craters located inside larger permanently shadowed craters, according to the press release by ISRO.
Temperatures extremely low
Since these regions are continuously shielded from both sunlight and thermal radiation, temperatures there remain extremely low, around 25 Kelvin. Such conditions make them ideal locations for preserving water-ice for very long periods.
The Chandrayaan-2 orbiter’s DFSAR instrument played a central role in the study. Operating in L- and S-band microwave frequencies, it is the first fully-polarimetric Synthetic Aperture Radar designed to study the Moon. The instrument allowed scientists to probe beneath the lunar surface and examine how radar signals behaved when reflected from the ground below.
Using advanced radar polarimetric analysis, researchers identified radar patterns that are consistent with the possible existence of subsurface ice beneath the floors of four doubly shadowed craters in the lunar South Polar Region.
The study also introduces a more refined radar-based method for identifying potential subsurface ice deposits. According to the researchers, Circular Polarization Ratio (CPR) values greater than 1 along with Degree of Polarization (DOP) values lower than 0.13 may indicate volumetric scattering linked to subsurface ice deposits.
DOP is a radar polarimetric parameter that measures how much of the reflected radar signal retains its original polarization state after interacting with surface or subsurface material. Reportedly, this method helps separate actual ice signatures from radar reflections caused by rough rocky terrain.
Among all the craters examined during the study, one crater measuring 1.1 km in diameter inside the larger Faustini crater emerged as the strongest candidate for subsurface ice presence. Scientists said the evidence comes not only from radar observations but also from the crater’s unusual lobate-rim morphology.
A lobate-rim morphology refers to a flow-like or lobed appearance around the crater rim. Researchers believe this shape may indicate that the impact responsible for creating the crater penetrated a subsurface ice layer, resulting in the distinctive structure.
