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India’s Chandrayaan-2 mission has provided fresh evidence suggesting the presence of subsurface water ice beneath the lunar south polar region, a discovery with significant implications for future lunar exploration and long-term human presence on the Moon. The findings, published by scientists from the Physical Research Laboratory (PRL), Ahmedabad, are based on observations made by the Dual Frequency Synthetic Aperture Radar (DFSAR) onboard the Chandrayaan-2 orbiter.

Launched by ISRO in July 2019, Chandrayaan-2 was India’s second lunar mission. While the Vikram lander lost communication during its landing attempt, the orbiter has continued to function successfully, generating valuable scientific data about the Moon.

DFSAR: A Unique Lunar Radar Instrument

The DFSAR is the first fully polarimetric synthetic aperture radar designed specifically for lunar studies. Operating in both L-band and S-band microwave frequencies, it can penetrate beneath the lunar surface and detect variations in subsurface composition, making it particularly useful for identifying water ice deposits hidden beneath layers of regolith.

Study and Methodology

The research focused on doubly shadowed craters situated within the Moon’s Permanently Shadowed Regions (PSRs) near the south pole. These regions never receive direct sunlight and maintain extremely low temperatures of about 25 Kelvin (-248°C), creating ideal conditions for the long-term preservation of water ice.

Scientists analysed radar data using two important parameters:

• Circular Polarization Ratio (CPR) > 1
• Degree of Polarization (DOP) < 0.13

Such radar signatures are considered potential indicators of volumetric scattering, a phenomenon commonly associated with subsurface ice deposits.

Key Findings

The study identified radar evidence suggesting possible subsurface ice beneath four doubly shadowed craters. The strongest indication came from a 1.1-km-wide crater located within the larger Faustini crater.

An additional clue emerged from the crater’s lobate-rim morphology, a geological feature that may indicate that the impact event penetrated an ice-rich subsurface layer. This strengthens the hypothesis that water ice could exist beneath the lunar surface rather than merely as surface frost.

Significance of the Discovery

The presence of water ice on the Moon has immense scientific and strategic importance:

• Supports future human missions by providing a potential source of drinking water.
• Can be split into hydrogen and oxygen for rocket fuel and life-support systems.
• Helps identify suitable sites for future lunar landers and bases.
• Advances understanding of the Moon’s geological and climatic history.
• Strengthens India's contribution to global lunar science and exploration.