ShadowCam search casts doubt on abundant lunar ice

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New observations by a team of US astronomers have cast fresh doubt on whether the lunar surface could host abundant water ice. Publishing their results in Science Advances, a team led by Shuai Li at the University of Hawaii at Manoa has shown that relatively pure ice (making up more than about 20–30% of the surface material) is likely absent from the moon's permanently shadowed regions.

Ice in the shadows

Across the solar system, several rocky bodies host permanently shadowed regions (PSRs). These environments form under fairly strict conditions: the body must have a small axial tilt, and host deep craters near its poles that never receive direct sunlight. With no atmosphere to trap heat, these regions are expected to remain extremely cold.

Even on Mercury, where daytime temperatures can exceed 400 °C, PSRs can act as long-term cold traps for water ice. Alongside Mercury, these deposits have also been confirmed on Ceres, the largest object in the asteroid belt. On the moon, however, evidence for ice has so far remained indirect, suggesting it may be far more sparse.

Searching for lunar ice

In their study, Li's team expanded this search using visible-wavelength images of several lunar PSRs captured by ShadowCam: a camera aboard the Korea Pathfinder Lunar Orbiter—South Korea's first lunar mission.

To detect solid ice, the researchers focused on two of its key optical properties. Compared with lunar regolith (the loose dust and rock covering the surface), water ice is both more reflective at visible wavelengths and more strongly forward-scattering: an effect which can be detected by pointing the camera in slightly different directions, and measuring how the surface brightness changes with viewing angle.

Astronomers generally acknowledge that lunar ice is unlikely to be pure, instead forming mixtures with regolith in varying proportions. These mixtures would produce different reflectance and scattering signatures depending on how much ice they contain.

Less than hoped

Unfortunately for some astronomers, the team's results will be a blow for hypotheses predicting abundant ice in lunar PSRs. To be reliably detected using reflectance and scattering, ice must make up at least about 20–30% of the surface mixture—but even at this level, Li and colleagues found no clear signal in any of the regions observed by ShadowCam.

If this result holds, it would effectively rule out the presence of abundant, near-surface water ice in the moon's permanently shadowed regions.

All the same, the findings certainly don't mean that ice is absent altogether. The team notes that some measurements could still be consistent with mixtures containing less than about 10% water ice—levels that remain below current detection limits for now.

In future studies, Li and his colleagues will now aim to probe this possibility more thoroughly by pushing detection thresholds below 1%. Even if small amounts of ice are confirmed, these results would be crucial: revealing access to vital resources for future crewed missions, and potentially offering new evidence about how water was first delivered to the moon. In turn, astronomers could gain new clues about the elusive early history of the solar system.

Written for you by our author Sam Jarman, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.

Publication details

Shuai Li et al, Searching for surficial water ice in lunar permanently shaded regions (PSRs) with ShadowCam, Science Advances (2026). DOI: 10.1126/sciadv.aec8211

Journal information: Science Advances

Key concepts

regolithplanetary sciencesThe Moon

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