Right now, a couple of feet above the surface of the Moon, a layer of dust is levitating. This is not a new development. Early photos of the Moon show the same phenomenon. What makes this dust float without air?

If we see dust floating around on Earth, we imagine that the wind is picking it up and throwing it around. If we saw it floating steadily in one place, we might be puzzled as to what kind of air currents can maintain a layer of dust so steadily, but we'd still chalk it up to the movements of gases, and we'd probably be right. On the Moon, where no atmosphere exists, the levitation of dust is a stumper, until we remember the photoelectric effect.

When photons hit a substance, and they have just the right wavelength, they knock electrons off of that substance. In this case, the photons are sunlight, and the substance is Moon dust. When the light from the sun hits the layer of dust on the Moon, it knocks electrons off the dust particles, giving them a slight positive charge. It also knocks electrons off the rock underneath the dust, giving it a positive charge. The positively-charged ground repels the positively-charged dust, and the dust rises up and forms a layer above the surface of the Moon.


The levitating dust layer isn't as thick as it could be, or as stable as it looks. When sunlight knocks electrons off the rock on the surface of the Moon, those electrons occasionally make their way up to the dust and climb aboard. Sometimes the dust can even become negatively charged. The negatively charged dust sinks to the surface of the Moon, but can be stripped of its electrons and made positive again. Some parts of the surface of the Moon can look like fountains because of this phenomenon. The rest of the Moon just pulls off this neat levitation trick and lets us wonder at its floating dust layer.

[Via Dust Gets a Charge in a Vacuum, Does the Moon Have Levitating Lunar Dust?]