Chandrayaan-2 Data Reveals Possible Subsurface Water Ice on the Moon

Nearly six years after its launch, India’s lunar mission Chandrayaan-2 has provided new scientific evidence suggesting the possible presence of subsurface water ice beneath the Moon’s south polar regions.The findings come from a detailed analysis of data collected by the Chandrayaan-2 orbiter, focusing on the Moon’s Permanently Shadowed Regions (PSRs) near the lunar south pole. These regions are areas that never receive sunlight, resulting in extremely low temperatures that allow volatile substances like water ice to remain stable for long periods.

Key Findings of the Research

¨     Evidence of Subsurface Ice: Scientists from the Physical Research Laboratory (PRL), Ahmedabad, used Chandrayaan-2’s Dual Frequency Synthetic Aperture Radar (DFSAR) data to investigate lunar south polar regions.

¨     The study identified radar signatures consistent with the possible presence of subsurface water ice beneath the floors of four doubly shadowed craters.

¨     Study of Doubly Shadowed Craters: The research focused on doubly shadowed craters, located within Permanently Shadowed Regions (PSRs).

¨     These regions never receive direct sunlight and remain extremely cold (~25 K), making them ideal reservoirs for preserving water ice over billions of years.

¨     New Radar-Based Ice Detection Criterion: Scientists developed a refined method to identify subsurface ice using Circular Polarization Ratio (CPR) > 1 and Degree of Polarization (DOP) < 0.13.

¨     This combination indicates volumetric scattering; a radar signature potentially associated with buried ice.

¨     Distinguishing Ice from Rocky Terrain: The CPR-DOP criterion helps separate genuine ice signatures from radar reflections caused by rough rocky surfaces, improving the reliability of ice detection.

¨     Strongest Evidence from Faustini Crater: A 1.1 km diameter crater inside the Faustini crater showed the strongest indications of subsurface ice.

The crater exhibits:

¨     High CPR values (>1)

¨     Low DOP values (<0.13)

¨     Distinctive lobate-rim morphology.

Technological Achievement: DFSAR became the first fully polarimetric Synthetic Aperture Radar (SAR) sent to study the Moon.Operating in both L-band and S-band frequencies, it can probe below the lunar surface and detect buried ice deposits.

Significance of the Research

¨     Improves Understanding of Lunar Polar Volatiles: The findings provide new insights into the distribution and long-term preservation of water ice and other volatile materials in the Moon’s polar regions.

¨     Supports Future Lunar Exploration: The study helps identify potential ice-rich locations suitable for future robotic and human missions to the Moon.

¨     Enables In-Situ Resource Utilisation (ISRU): Lunar water ice could be utilized to produce drinking water, breathable oxygen, and hydrogen-oxygen rocket fuel for sustained lunar operations.

¨     Reduces Dependence on Earth-Supplied Resources: The availability of local water resources could significantly reduce the cost and logistical challenges of long-duration lunar missions.

¨     Strengthens India’s Contribution to Lunar Science: The discovery underscores the continued scientific success of Chandrayaan-2 and reinforces India’s growing role in global lunar exploration.

¨     Aids Future South Pole Missions: The findings provide valuable guidance for future missions targeting the Moon’s south polar region, including landing site selection and resource exploration.

Chandrayaan-2

¨     Chandrayaan-2 was India’s second lunar exploration mission launched on 22 July 2019 by the GSLV Mk III-M1 rocket from Satish Dhawan Space Centre, Sriharikota.

The mission consisted of

¨     Orbiter

¨     Vikram Lander

¨     Pragyan Rover

Major Objectives

¨     Study lunar surface geology and mineralogy.

¨     Map lunar topography and morphology.

¨     Investigate the lunar exosphere.

¨     Search for and quantify water ice in polar regions.

¨     Examine the Moon’s surface and shallow subsurface properties.

¨     Mission Outcome: On 7 September 2019, communication with the Vikram lander was lost during the final descent phase.

¨     However, the Orbiter remained healthy and fully operational, continuing scientific observations around the Moon.

¨     Orbiter Orbit: The Chandrayaan-2 Orbiter currently operates in a 100 km × 100 km polar orbit around the Moon.

Major Orbiter Payloads

¨     CLASS (Large Area Soft X-ray Spectrometer) – Elemental mapping of the lunar surface.

¨     CHACE-2 – Studies the lunar exosphere.

¨     DFSAR (Dual Frequency Synthetic Aperture Radar) – Detects water ice and studies subsurface features.

¨     IIRS (Imaging Infra-Red Spectrometer) – Maps minerals and water/hydroxyl signatures.

¨     DFRS (Dual Frequency Radio Science Experiment) – Studies the lunar ionosphere.