Scientists found that the Moon’s faint dust cloud is thicker on the sunlit side because micrometeoroid impacts on hot ground eject more material and send particles higher. The cloud is extremely tenuous — about 0.004 particles per cubic meter at most — but spans hundreds of kilometers. Soil compactness also affects ejecta: compact patches release more dust while loose regolith absorbs impact energy. Researchers will next test whether Mercury, with far higher daytime temperatures, hosts an even more asymmetric dust envelope.
The Moon’s Lopsided Dust Cloud: Why Its Faint Halo Leans Toward the Sun
Scientists found that the Moon’s faint dust cloud is thicker on the sunlit side because micrometeoroid impacts on hot ground eject more material and send particles higher. The cloud is extremely tenuous — about 0.004 particles per cubic meter at most — but spans hundreds of kilometers. Soil compactness also affects ejecta: compact patches release more dust while loose regolith absorbs impact energy. Researchers will next test whether Mercury, with far higher daytime temperatures, hosts an even more asymmetric dust envelope.
07:16 PM, 11/13/2025Science
The Moon’s Lopsided Dust Cloud
Summary: The Moon is surrounded by a faint, asymmetric cloud of dust that consistently favors the sunlit side. New simulations suggest that temperature-driven differences in how lunar soil responds to micrometeoroid impacts explain the cloud’s unusual shape.
What is the cloud?
Micrometeoroids — tiny fragments of rock roughly 1 mm across — continuously strike the lunar surface. Several tons of this cosmic grit hit the Moon every day, grinding small surface rocks into fine powder. When these micrometeoroids slam into the ground, they eject dust and regolith particles upward, producing a huge but extremely tenuous cloud that stretches for hundreds of kilometers above the surface.
Why you can’t see it
Although the dust veil spans vast distances, it is far too sparse to be visible to the naked eye. "The maximum density measured was only 0.004 particles per cubic meter," said Sebastian Verkecke, lead author of the new study, in an interview with Live Science. That tiny population is not evenly distributed around the Moon.
Why the cloud is lopsided
Temperature swings are the key factor. The lunar surface undergoes extreme thermal variation: daytime temperatures can reach about 285°C, while night temperatures can drop to roughly −183°C. Researchers ran computer simulations of micrometeoroid impacts on surfaces set to those day- and night-side temperatures to see how ejecta production changes with heat.
The models showed two main effects:
- Heat increases ejecta: Warmer surfaces release more material and launch particles higher, so impacts on the sunlit side seed a denser cloud.
- Soil compactness matters: Tightly packed regolith tends to fling more dust when struck, whereas fluffier, looser soils absorb more impact energy and produce less ejecta.
Together, these effects cause more dust to be lofted and travel farther from sunlit regions, while cold, night-side impacts produce far less escaping material. Over time this imbalance builds a persistent, skewed dust envelope that consistently leans toward the hemisphere facing the Sun, with the greatest concentration near the dawn terminator.
“Impacts on hotter, sunlit ground send grains higher and farther than identical strikes on cold ground, creating a long-term asymmetry in the Moon’s dust cloud,” said Sebastian Verkecke.
What’s next?
The research team plans to extend their approach to other airless bodies. Mercury is an especially intriguing target: because it experiences much higher daytime temperatures, it may host an even more pronounced, "wonky" dust cloud. Studying these dusty envelopes can help us better understand surface processes across the inner solar system and the hazards they may pose to spacecraft.