Scientists studying data from India’s Chandrayaan-2 mission have discovered new evidence that suggests there may be ice under the moon’s surface near the south polar region. These results come from a detailed analysis conducted by researchers at the Physical Research Laboratory (PRL) in Ahmedabad, using observations from the Chandrayaan-2 orbiter’s dual-frequency synthetic aperture radar (DFSAR).
The research focused on the permanently shaded regions (PSRs) near the Moon’s south pole, regions that never receive sunlight and remain among the coldest places in the solar system. Within these areas, scientists closely examined what they described as “double-shadow craters,” which are small craters located within larger, permanently shadowed craters, according to the ISRO press release.
Temperatures are very low
Since these areas are constantly protected from sunlight and thermal radiation, temperatures there remain very low, around 25 K. Such conditions make them ideal locations for maintaining water ice for very long periods.
The Chandrayaan-2 orbiter’s DFSAR instrument played a central role in the study. Operating in the L and S microwave bands, this radar is the first fully polarized synthetic aperture radar designed to study the Moon. The instrument allowed scientists to probe beneath the surface of the moon and examine how radar signals behave when reflected from the Earth below.
Using advanced radar polarimetric analysis, researchers identified radar patterns consistent with the possible presence of subsurface ice beneath the floors of four double-shadowed craters in the lunar south polar region.
The study also presents a more accurate 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 less than 0.13 may indicate volumetric dispersion associated with subsurface ice deposits.
DOP is a radar polarimetric parameter that measures how much the reflected radar signal retains its original polarization state after interacting with surface or subsurface materials. Scientists say this method helps separate actual ice signatures from radar reflections caused by rugged, rocky terrain.
Of all the craters examined during the study, a 1.1-kilometre-diameter crater within the larger Faustini Crater emerged as the strongest candidate for the presence of subsurface ice. Scientists said the evidence comes not only from radar observations, but also from the unusual shape of the lobed crater rim.
Lobed rim morphology refers to a flow-like or lobulated appearance around the crater rim. The researchers believe this shape may indicate that the impact responsible for creating the crater penetrated an ice layer beneath the surface, creating the distinctive structure.
