Initial assessments following the Apollo missions suggested the Moon was entirely devoid of water. However, decades of subsequent research revealed trace amounts, with tantalizing hints of substantial ice deposits in permanently shadowed regions (PSRs) near the lunar south pole. A new study in Science Advances casts doubt on these expectations, suggesting lunar PSRs contain significantly less water than previously estimated—and many may lack surface ice altogether.
ShadowCam Data Reveals Limited Ice Presence
Researchers analyzed high-resolution images from NASA’s ShadowCam instrument aboard the Korea Pathfinder Lunar Orbiter. The findings indicate that in most of the Moon’s darkest craters, water constitutes less than 20–30% of the material by weight. Many PSRs appear to have no surface ice at all. Planetary geologist Shuai Li, lead author of the study, states, “Based on the data we have now… we are pretty sure there is ice on the surface,” but the quantity remains a critical unknown.
This scarcity has implications for future lunar missions, which may have hoped to extract water for drinking, propellant, or scientific analysis. The amount of available water will directly affect the viability of long-term lunar bases.
Origins and Significance of Lunar Water
Most of the Moon’s water likely arrived via asteroid and comet impacts roughly four billion years ago. Mapping its distribution could provide insights into the composition of early solar system projectiles—a key question in planetary science. The water may not be directly deposited by impacts, but rather accumulated through a “cold trapping” process where water vapor from impacts or solar wind condenses in frigid craters. This process is also observed on Mercury and Ceres, suggesting common mechanisms for water accumulation in cold, dark regions across the solar system.
Future Exploration Needed for Definitive Answers
The study sets an upper limit on surface ice abundance, but leaves open the possibility of subsurface deposits. Better instruments are needed to detect even trace amounts of water in lunar soil. However, many experts believe that in-situ exploration—including robotic and human missions—will be essential for obtaining definitive answers. As David Kring, leader of the Center for Lunar Science & Exploration, notes, orbital measurements are valuable, but “boots on the ground” exploration is the only way to resolve this mystery.
The lunar water quest is far from over. While current evidence suggests limited surface reserves, further investigation will be vital to determine whether the Moon can serve as a sustainable source of water for future space exploration.
