Lunar dust cloud may come from comet debris
Earth’s moon has no atmosphere. This means that many things that we can take for granted on Earth don’t, or at least shouldn’t, really happen there. One example would be dust hanging in the air. On Earth, dust particles can happily bounce around among the multitude of molecules that make up our air, but on the Moon there really shouldn’t be that much of anything to suspend a dust particle in. Despite this, the Moon has been found to have a persistent dust cloud in one big clump, and it’s unclear why that’s happening.
Theories for the dust’s origin have included electro-static buildup as well as dropped dust from passing asteroids. But the latest measurements from the LADEE spacecraft indicate that this may be a buildup of comet debris. The oblong shape of the dust patch is a better match for the scattered bits of a comet, which would be streaking by much more quickly than say, an asteroid (“like an airplane,” as my first grader puts it.) The deposited dust then collects and actually rises back up into the “air,” up to 100 km above the surface, before falling back down.
This is slightly different than what astronauts in the 1960s reported looked like dust clouds. During those few visits to the moon, “bright rays and glowing streamers” of what seemed like dust were seen just before sunrise, which require a much thicker concentration of particulate than what the LADEE data reports. For some perspective, the Moon seems to have around five tons of dust hitting it every day (with around 120 kg of dust suspended at any given moment.) However, Earth is bombarded with around 100 tons daily, so the quantities we’ve currently measured aren’t going to be creating the god rays the astronauts saw.
Source: Lopsided Cloud of Dust Discovered Around the Moon by Nadia Drake, National Geographic