First Report on the Detection of Scandium (Sc) in the Grimaldi Basin: Insights into Subsurface Lunar Geochemistry

The Moon is not a static, dead rock, but a world shaped by a violent history of collisions and a deep, complex chemical past. For decades, planetary scientists have proposed that shortly after the Moon formed, it was covered by a global ocean of molten rock. As this magma ocean cooled and solidified, heavy minerals sank while lighter ones floated, creating distinct layers. The final, sticky residue of this cooling process was rich in specific elements like potassium, rare earth elements, and phosphorus, a mixture scientists call KREEP. Because this material is dense and incompatible with the early crust, it was thought to have settled deep underground, hidden beneath miles of surface dust and rock. For a long time, the only place this KREEP material was clearly visible was in a specific region on the Moon's near side, leading scientists to believe it was trapped there. The question remained: was this material unique to that one area, or was it scattered across the entire Moon, buried just out of sight?

A new study published in 2026 offers a surprising answer by looking at a place where the Moon's surface has been recently torn open. Researchers used data from the Chandrayaan-2 spacecraft, which orbits the Moon, to watch for the chemical fingerprints left behind when space rocks crash into the lunar surface. By combining observations of meteoroid impacts with sensitive X-ray measurements, the team discovered a rare element called scandium in the Grimaldi Basin, a large crater on the far western edge of the Moon's near side. This basin lies far outside the known KREEP-rich region, suggesting that the chemical leftovers of the Moon's formation are not confined to a single location but are likely buried beneath the surface across the globe, waiting to be dug up by a cosmic collision.

The researchers focused their attention on the Grimaldi Basin, a vast depression located at 4 degrees south latitude and 66 degrees west longitude. They were looking for evidence of a meteoroid impact that had happened recently enough to expose fresh material from deep underground. Using a network of telescopes on Earth, they identified a specific impact event that occurred on November 3, 2019, where a space rock struck the basin. This impact was powerful enough to dig a crater roughly 22.8 meters wide and excavate material from a depth of about 2.2 meters. The team then turned to the Large Area Soft X-ray Spectrometer, an instrument aboard the Chandrayaan-2 orbiter, to analyze the chemical composition of the fresh debris left behind by this crash.

The instrument works by detecting X-rays that bounce off the lunar surface when hit by energy from the Sun. By measuring the specific energy of these X-rays, scientists can identify which elements are present. In the data collected after the November 2019 impact, the researchers found a clear signal for scandium, a trace element that had never been detected in this specific region before. Alongside scandium, they also found signatures of potassium and phosphorus, the other key components of the KREEP mixture. This combination of elements is significant because it matches the chemical profile expected from the deep, residual layers of the ancient magma ocean. The detection was not a fluke; the signal was strong enough to be distinguished from background noise, and it appeared only after the impact, confirming that the material had been brought up from below the surface.

To ensure this discovery was real, the team compared the Grimaldi Basin findings with data from other impact sites on the Moon. They looked at two other recent crashes, one in the Mare Serenitatis and another in the Mare Fecunditatis. While these impacts also brought up common elements like magnesium, aluminum, and silicon, they did not show any sign of scandium or the KREEP signature. This contrast highlights that the Grimaldi Basin is a genuine chemical anomaly. The fact that the KREEP elements were found only in the deepest excavation, at a depth of roughly 2.2 meters, suggests that this material is not spread evenly through the top layer of dust. Instead, it is likely sequestered in deeper pockets, shielded from view until a sufficiently large impact digs it up.

The location of this discovery is perhaps the most important part of the story. The Grimaldi Basin is situated well outside the Procellarum KREEP Terrane, the region where scientists previously thought all this material was concentrated. Finding these elements here suggests that the distribution of the Moon's chemical history is more complex than previously believed. It implies that the KREEP-rich material might be more globally distributed than once thought, hidden beneath the regolith in various locations across the lunar surface. This does not contradict the theory of a global magma ocean; rather, it supports it by showing that the chemical separation process likely happened everywhere, but the resulting materials were buried and are only now being revealed by random impacts.

The study also confirmed that the instrument used to make these measurements is incredibly sensitive. The detection of scandium occurred during a period of low solar activity, a time when the Sun's X-ray output is weak and usually makes it difficult to spot such faint signals. The fact that the team could still identify the element suggests that the local concentration of these materials is higher than expected, or that the instrument is capable of resolving these details even under challenging conditions. This finding opens a new door for understanding the Moon's interior. It shows that meteoroid impacts act as natural drills, exposing deep-seated geochemical reservoirs that orbital instruments cannot see through the surface dust.

Ultimately, this research changes how we view the Moon's chemical map. The presence of scandium and KREEP elements in the Grimaldi Basin indicates that the Moon's subsurface is chemically diverse and that the remnants of its fiery birth are not locked away in just one corner. The study suggests that if we were to dig deep enough in other parts of the Moon, we might find similar pockets of these ancient materials. While the detection is specific to this one impact site, it provides compelling evidence that the processes which shaped the early Moon were global in scale. The Moon's surface may look uniform to the naked eye, but beneath the dust, it holds a complex history of differentiation and mixing, waiting for the next cosmic hammer to reveal its secrets.