Scientists Just Solved the Mystery of the Moon’s Lopsided Dust Halo

For decades, scientists have known the Moon's faint dust halo sits unevenly around it — denser over the sunlit side than on the dark side. A new study suggests the culprit is the Moon's extreme day–night temperature swings. Using computer models, the team found that daytime meteor impacts fling about 6–8% more dust skyward than cold-night strikes, making the dayside dust thicker, skewing the cloud toward sunlight.

Heat and the Skewed Halo

According to the new study, the team simulated micrometeoroid strikes on hot daytime soil versus cold-night soil. Daytime impacts released 6–8% more dust and lofted more particles into orbit. Sébastien Verkercke, a postdoctoral researcher at the Centre National D'Etudes Spatiales (France's national space agency) in Paris and the new study's first author, explains, “The ejected dust grains are then individually tracked to monitor their distribution in space”, meaning midday hits throw extra dust aloft.

NASA warns lunar dust “can be damaging to everything from lunar landers to spacesuits and human lungs if inhaled”, highlighting why tracking the dust matters for space missions. Even Mercury's bigger day–night swings should amplify this asymmetry — ESA's BepiColombo probe may soon test it.

Meteoric Origins of the Lunar Dust

Micrometeoroids constantly pelt the Moon's surface, chipping rock into dust. Each tiny strike sends grains aloft, forming a tenuous halo. In 2015, NASA's LADEE orbiter confirmed a dust halo hundreds of miles above the Moon.

CU Boulder physicist Mihály Horányi notes even “a single dust particle from a comet striking the Moon's surface lofts thousands of smaller dust specks into the airless environment”, with regular impacts maintaining the haze. Curiously, the cloud is asymmetrical — denser on the sunlit side near dawn.